ACTG2-related disorders are a subset of visceral myopathy with variable involvement of the bladder and intestine. Bladder involvement can range from neonatal megacystis and megaureter (with its most extreme form of prune belly syndrome) at the more severe end, to recurrent urinary tract infections and bladder dysfunction at the milder end. Chronic bladder dysfunction carries a high risk for urinary tract infections, dilation of the upper urinary tract, and impaired renal function. Intestinal involvement can range from malrotation, neonatal manifestations of microcolon, megacystic microcolon intestinal hypoperistalsis syndrome (MMIHS), and chronic intestinal pseudoobstruction (CIPO) in neonates, children, and adults. Affected infants (with or without evidence of intestinal malrotation) often present with feeding intolerance and findings of non-mechanical bowel obstruction that persist after successful surgical correction of malrotation. Individuals who develop manifestations of CIPO in later childhood or adulthood often experience episodic waxing and waning of bowel motility. They may undergo frequent abdominal surgeries (perhaps related to malrotation or adhesions causing mechanical obstruction) resulting in resection of dilated segments of bowel, often becoming dependent on total parenteral nutrition (TPN). [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK299311]

Baraitser-Winter Cerebrofrontofacial Syndrome

CHD2-Related Neurodevelopmental Disorders

Action Myoclonus - Renal Failure Syndrome

DYRK1A-Related Intellectual Disability Syndrome

Autosomal Dominant Leukodystrophy with Autonomic Disease

Xq28 Duplication Syndrome, Int22h1/Int22h2 Mediated

ADNP-Related Intellectual Disability and Autism Spectrum Disorder

15q Duplication Syndrome and Related Disorders

FOXP2-Related Speech and Language Disorders

Multicentric Osteolysis Nodulosis and Arthropathy

SCN8A-Related Epilepsy with Encephalopathy

GRIN2A-Related Speech Disorders and Epilepsy

Hereditary Fibrosing Poikiloderma with Tendon Contractures, Myopathy, and Pulmonary Fibrosis

Primary Familial and Congenital Polycythemia

Beta-Propeller Protein-Associated Neurodegeneration

SUCLG1-Related Mitochondrial DNA Depletion Syndrome, Encephalomyopathic Form with Methylmalonic Aciduria

FBXL4-Related Encephalomyopathic Mitochondrial DNA Depletion Syndrome

PURA-Related Neurodevelopmental Disorders

SAMD9L-Related Ataxia-Pancytopenia Syndrome

SLC6A3-Related Dopamine Transported Deficiency Syndrome

Complete Plasminogen Activator Inhibitor 1 Deficiency

PRRT2-Associated Paroxysmal Movement Disorders

TANGO2-Related Metabolic Encephalopathy and Arrhythmias

INSR-Related Severe Syndromic Insulin Resistance

Hyperphosphatemic Familial Tumoral Calcinosis

Congenital Insensitivity to Pain Overview

NGLY1-Related Congenital Disorder of Deglycosylation

Mitochondrial DNA Maintenance Defects Overview

Maturity-Onset Diabetes of the Young Overview

GRIN2B-Related Neurodevelopmental Disorder

Leber Congenital Amaurosis / Early-Onset Severe Retinal Dystrophy Overview

AP-4-Associated Hereditary Spastic Paraplegia

PPP2R5D-Related Neurodevelopmental Disorder

SLC12A5-Related Epilepsy of Infancy with Migrating Focal Seizures

Megacystis-Microcolon-Intestinal Hypoperistalsis Syndrome Overview

FKBP14 Kyphoscoliotic Ehlers-Danlos Syndrome

Mitochondrial Short-Chain Enoyl-CoA Hydratase 1 Deficiency

GRIN1-Related Neurodevelopmental Disorder

Retinal Vasculopathy with Cerebral Leukoencephalopathy and Systemic Manifestations

ISCA1-Related Multiple Mitochondrial Dysfunctions Syndrome

Hereditary Distal Renal Tubular Acidosis

RPE65-Related Leber Congenital Amaurosis / Early-Onset Severe Retinal Dystrophy

Floating-Harbor syndrome (FHS) is characterized by typical craniofacial features; low birth weight, normal head circumference, and short stature; bone age delay that normalizes between ages six and 12 years; skeletal anomalies (brachydactyly, clubbing, clinodactyly, short thumbs, prominent joints, clavicular abnormalities); severe receptive and expressive language impairment; hypernasality and high-pitched voice; and intellectual disability that is typically mild to moderate. Difficulties with temperament and behavior that are present in many children tend to improve in adulthood. Other features can include: hyperopia and/or strabismus; conductive hearing loss; seizures; gastroesophageal reflux; renal anomalies (e.g., hydronephrosis/renal pelviectasis, cysts, and/or agenesis) and genital anomalies (e.g., hypospadias and/or undescended testes). [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK114458]
Rotor syndrome is characterized by mild conjugated and unconjugated hyperbilirubinemia which usually begins shortly after birth or in childhood. Jaundice may be intermittent. Conjunctival icterus may be the only clinical manifestation. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK114805]
The four children with carbonic anhydrase VA (CA-VA) deficiency reported to date presented between day two of life and age 20 months with hyperammonemic encephalopathy (i.e., lethargy, feeding intolerance, weight loss, tachypnea, seizures, and coma). Data on long-term follow up are limited (the oldest known patient is age 7 years). Two of the four children showed normal psychomotor development and two showed mild learning difficulties and delayed motor skills. Seven additional children diagnosed with CA-VA deficiency (but not yet published) presented similarly. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK284774]
Nicolaides-Baraitser syndrome (NCBRS) is characterized by sparse scalp hair, prominence of the inter-phalangeal joints and distal phalanges due to decreased subcutaneous fat, characteristic coarse facial features, microcephaly, seizures, and developmental delay/intellectual disability. Seizures are of various types and can be difficult to manage. Developmental delay/intellectual disability (ID) is severe in nearly a half, moderate in a third, and mild in the remainder. Nearly a third never develop speech or language skills. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK321516]
DNMT1-related dementia, deafness, and sensory neuropathy (HSAN IE) is a degenerative disorder of the central and peripheral nervous systems characterized by sensory impairment of the distal lower extremities, loss of sweating (sudomotor function) on the distal aspects of the upper and lower limbs, sensorineural hearing loss, and dementia. Affected persons are normal in their youth but begin to manifest progressive sensory neuropathy and moderate to severe progressive sensorineural deafness by age 20 to 35 years. The sensory alterations result in gait unsteadiness from sensory ataxia and mutilating ulcers and/or amputations of distal extremities in approximately 50% of affected persons. Dementia usually manifests by the fourth decade. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK84112]
SYNE1-related autosomal recessive cerebellar ataxia (also known as autosomal recessive cerebellar ataxia type 1 or ARCA1) is characterized by onset of cerebellar ataxia and/or dysarthria at a mean age of 31 years (range 17-46 years). Over time, all affected individuals develop significant dysarthria and ataxia. Other associated features can include dysmetria, brisk lower-extremity tendon reflexes, and minor abnormalities in ocular saccades and pursuit. Disease progression is slow, resulting in moderate disability. Life expectancy appears to be normal. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1379]
Spinocerebellar ataxia type 11 (SCA11) is characterized by progressive cerebellar ataxia and abnormal eye signs (jerky pursuit, horizontal and vertical nystagmus). Pyramidal features, peripheral neuropathy, and dystonia are seen on occasion. Four families have been reported to date: one each from the UK, France, Germany, and Pakistan. In them, age of onset ranged from the early teens to the mid 20s. Life span is normal. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1757]
DFNX1 Nonsyndromic Hearing Loss and Deafness
DFNX1 nonsyndromic hearing loss and deafness is part of the spectrum of PRPS1-related disorders. The hearing loss in males is bilateral, sensorineural, and moderate to profound; prelingual or postlingual in onset; and progressive or non-progressive. The hearing in female carriers can be normal or abnormal. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK57098]
SUCLA2-Related Mitochondrial DNA Depletion Syndrome, Encephalomyopathic Form with Methylmalonic Aciduria
SUCLA2-related mitochondrial DNA (mtDNA) depletion syndrome is characterized by onset of severe hypotonia in early infancy (birth to five months); severe muscular atrophy with failure to achieve independent ambulation; progressive scoliosis or kyphosis; dystonia and/or hyperkinesias (i.e., athetoid or choreiform movements); epilepsy (infantile spasms or generalized convulsions with onset from birth to three years) in a few children; postnatal growth retardation; and severe sensorineural hearing impairment. The outcome is poor with early lethality. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK6803]
Arginase deficiency in untreated individuals is characterized by episodic hyperammonemia of variable degree that is infrequently severe enough to be life threatening or to cause death. Most commonly, birth and early childhood are normal. Untreated individuals have slowing of linear growth at age one to three years, followed by development of spasticity, plateauing of cognitive development, and subsequent loss of developmental milestones. If untreated, arginase deficiency usually progresses to severe spasticity, loss of ambulation, complete loss of bowel and bladder control, and severe intellectual disability. Seizures are common and are usually controlled easily. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1159]
In the families described to date, the phenotype of spinocerebellar ataxia type 13 (SCA13) has ranged from slowly progressive childhood-onset cerebellar gait ataxia associated with cerebellar dysarthria and often accompanied by mild intellectual disability and occasional seizures to adult-onset progressive ataxia. Life span is not shortened and many persons live beyond age 70 years, but assistance with gait may be required as the disease progresses. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1225]
Spinocerebellar ataxia type 20 (SCA20) is characterized by a slowly progressive ataxia and dysarthria. Approximately two thirds of those affected also display palatal tremor ("myoclonus") and/or abnormal phonation clinically resembling spasmodic adductor dysphonia. Dysarthria, which may be abrupt in onset, precedes the onset of ataxia in about two thirds of affected individuals, sometimes by a number of years. Hypermetric horizontal saccades (without nystagmus or disturbance of vestibulo-ocular reflex gain) are seen in about half of affected persons. Although minor pyramidal signs (brisk knee jerks, crossed adductor spread) may be seen, spasticity and extensor plantar responses are not. Cognition is normal. Clinical information is based on the findings in 16 personally examined affected members of a single Australian family of Anglo-Celtic descent. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1471]
Autosomal Dominant Tubulointerstitial Kidney Disease, MUC1-Related
Medullary cystic kidney disease type 1 (MCKD1) is a kidney-specific disorder. It is characterized by slowly progressive tubulo-interstitial disease that leads to end-stage renal disease (ESRD) and the need for dialysis or kidney transplantation. ESRD typically occurs in adulthood but is extremely variable, occurring at any age between 20 and 70 yrs. Unlike in UMOD-associated kidney disease (medullary cystic kidney disease type 2), gout in MCKD1 is a sequela of kidney failure and not a primary manifestation of the disorder. Hypertension also appears to be a sequela of the disease, occurring after the onset of kidney failure. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK153723]
Arts syndrome, which is part of the spectrum of PRPS1-related disorders, is characterized by profound congenital sensorineural hearing impairment, early-onset hypotonia, delayed motor development, mild to moderate intellectual disability, ataxia, and increased risk of infection, all of which (with the exception of optic atrophy) present before age two years. Signs of peripheral neuropathy develop during early childhood. Twelve of 15 boys from the two Dutch families reported with Arts syndrome died before age six years of complications of infection. Carrier females can show late-onset (age >20 years) hearing impairment and other findings. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK2591]
PRICKLE1-Related Progressive Myoclonus Epilepsy with Ataxia
PRICKLE1-related progressive myoclonus epilepsy (PME) with ataxia is characterized by myoclonic seizures (lightning-like jerks), generalized convulsive seizures, varying degrees of neurologic decline especially manifest as ataxia, and normal intellectual abilities. Onset of symptoms is between ages five and ten years. Action myoclonus may affect the limbs or bulbar muscles, sometimes with spontaneous myoclonus of facial muscles. Marked dysarthria may occur. Seizures can be myoclonic or tonic-clonic and are often nocturnal. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK9674]
Amish lethal microcephaly is characterized by microcephaly and early death. The occipitofrontal circumference is typically six to 12 standard deviations below the mean; anterior and posterior fontanels are closed at birth and facial features are distorted. The average life span is between five and six months. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1365]
Hereditary Motor and Sensory Neuropathy with Agenesis of the Corpus Callosum
Hereditary motor and sensory neuropathy with agenesis of the corpus callosum (HMSN/ACC), a neurodevelopmental and neurodegenerative disorder, is characterized by severe progressive sensorimotor neuropathy with resulting hypotonia, areflexia, and amyotrophy and variable degrees of dysgenesis of the corpus callosum. Mild-to-severe intellectual disability and "psychotic episodes" during adolescence are observed. Sensory modalities are moderately to severely affected beginning in infancy. The average age of onset of walking is 3.8 years; the average age of loss of walking is 13.8 years; the average age of death is 33 years. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1372]
MEGDEL (3-methylglutaconic aciduria with deafness, encephalopathy and Leigh-like) syndrome is characterized in neonates by hypoglycemia and a sepsis-like clinical picture for which no infectious agent can be found. During the first year of life feeding problems, failure to thrive, and/or truncal hypotonia become evident; many infants experience (transient) liver involvement ranging from undulating transaminases to prolonged hyperbilirubinemia and near-fatal liver failure. By age two years progressive deafness, dystonia, and spasticity prevent further psychomotor development and/or result in loss of acquired skills. Affected children are completely dependent on care for all activities of daily living; speech is absent. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK195853]
Glycogen storage disease type VI (GSD VI), a disorder of glycogenolysis caused by deficiency of hepatic glycogen phosphorylase, is characterized in the untreated child by hepatomegaly, growth retardation, ketotic hypoglycemia after an overnight fast, and mild hypoglycemia after prolonged fasting (e.g., during an illness). It is usually a relatively mild disorder that presents in infancy and childhood; however, severe and recurrent hypoglycemia, severe hepatomegaly, and post-prandial lactic acidosis have been described. The risk of hepatic adenoma formation in late childhood and adulthood is theoretically increased. Clinical and biochemical abnormalities may resolve with age; most adults are asymptomatic. Hypoglycemia can occur during pregnancy. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK5941]
Familial lipoprotein lipase (LPL) deficiency usually presents in childhood and is characterized by very severe hypertriglyceridemia with episodes of abdominal pain, recurrent acute pancreatitis, eruptive cutaneous xanthomata, and hepatosplenomegaly. Clearance of chylomicrons from the plasma is impaired, causing triglycerides to accumulate in plasma and the plasma to have a milky ("lactescent" or "lipemic") appearance. Symptoms usually resolve with restriction of total dietary fat to ≤20 grams/day. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1308]
Biotin-Thiamine-Responsive Basal Ganglia Disease
Biotin-thiamine-responsive basal ganglia disease (BTBGD) is characterized by recurrent subacute encephalopathy manifest as confusion, seizures, ataxia, dystonia, supranuclear facial palsy, external ophthalmoplegia, and/or dysphagia which - if left untreated - can eventually lead to coma and even death. Dystonia and cogwheel rigidity are nearly always present; hyperreflexia, ankle clonus, and Babinski responses are common. Hemiparesis or quadriparesis may be seen. Episodes are often triggered by febrile illness or mild trauma or surgery. Less frequently, BTBGD presents as chronic or slowly progressive dystonia, seizures, and/or psychomotor delay. Although onset is usually in childhood (ages three to ten 10 years), it is extremely variable, ranging from the newborn period to adulthood. Prompt administration of biotin and thiamine early in the disease course results in partial or complete improvement within days. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK169615]
Mitochondrial Membrane Protein-Associated Neurodegeneration
Mitochondrial membrane protein-associated neurodegeneration (MPAN) is characterized initially by gait changes followed by progressive spastic paresis, progressive dystonia (which may be limited to the hands and feet or more generalized), neuropsychiatric abnormalities (e.g., emotional lability, depression, anxiety, impulsivity, compulsions, hallucinations, perseveration, inattention, and hyperactivity), and cognitive decline. Additional early findings can include dysphagia, dysarthria, optic atrophy, axonal neuropathy, parkinsonism, and bowel/bladder incontinence. Survival is usually well into adulthood. End-stage disease is characterized by severe dementia, spasticity, dystonia, and parkinsonism. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK185329]
Feingold syndrome 1 is characterized by digital anomalies (shortening of the 2nd and 5th middle phalanx of the hand, clinodactyly of the 5th finger, syndactyly of toes 2-3 and/or 4-5, thumb hypoplasia), microcephaly, facial dysmorphism (short palpebral fissures and micrognathia), gastrointestinal atresias (primarily esophageal and/or duodenal), and mild to moderate learning disability. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK7050]
X-Linked Spondyloepiphyseal Dysplasia Tarda
In adults, X-linked spondyloepiphyseal dysplasia tarda (X-linked SEDT) is characterized by disproportionately short stature with short trunk and arm span significantly greater than height. At birth, affected males are normal in length and have normal body proportions. Affected males exhibit retarded linear growth beginning around age six to eight years. Final adult height is typically 137-163 cm. Progressive joint and back pain with osteoarthritis ensues; hip, knee, and shoulder joints are commonly involved but to a variable degree. Hip replacement is often required as early as age 40 years. Interphalangeal joints are typically spared. Motor and cognitive milestones are normal. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1145]
ATP7A-Related Copper Transport Disorders
Menkes disease, occipital horn syndrome (OHS), and ATP7A-related distal motor neuropathy (DMN) are disorders of copper transport caused by mutations in the copper-transporting ATPase gene (ATP7A). [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1413]
Proopiomelanocortin (POMC) deficiency is characterized by severe, early-onset hyperphagic obesity and congenital adrenal insufficiency, the latter secondary to corticotropin (ACTH) deficiency. In the first months of life most children with POMC deficiency experience exponential weight gain, hyperphagia, cholestasis, and adrenal insufficiency. Weight gain continues rapidly, so that by the end of the first year of life obesity is severe (i.e., weight well above the 98th centile for age, without increased height). Red hair and Fitzpatrick type 1 skin (which always burns and never tans) are common, but not invariably present. On occasion central hypothyroidism (resulting from thyroid stimulating hormone [TSH] deficiency), adolescent-onset growth hormone (GH) deficiency, and adolescent-onset hypogonadotrophic hypogonadism resulting from deficiency of luteinizing hormone (LH) and follicule stimulating hormone (FSH) can be observed. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK174451]
Congenital stromal corneal dystrophy is characterized by the presence of bilateral corneal opacities that can be seen at or shortly after birth. The surface of the cornea is normal or slightly irregular; small opacities seen throughout the stroma of the entire cornea give the cornea a cloudy appearance. Strabismus is common. Nystagmus is uncommon. Most individuals undergo penetrating keratoplasty in late adolescence or early adulthood with good results. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK2690]
Congenital contractural arachnodactyly (CCA) is characterized by a Marfan-like appearance (tall, slender habitus in which arm span exceeds height) and long, slender fingers and toes (arachnodactyly). Most affected individuals have “crumpled” ears that present as a folded upper helix of the external ear and most have contractures of major joints (knees and ankles) at birth. The proximal interphalangeal joints also have flexion contractures (i.e., camptodactyly), as do the toes. Hip contractures, adducted thumbs, and club foot may occur. The majority of affected individuals have muscular hypoplasia. Contractures usually improve with time. Kyphosis/scoliosis is present in about half of all affected individuals. It begins as early as infancy, is progressive, and causes the greatest morbidity in CCA. Dilatation of the aorta is occasionally present. Infants have been observed with a severe/lethal form characterized by multiple cardiovascular and gastrointestinal anomalies in addition to the typical skeletal findings. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1386]
Hereditary spastic paraplegia 8 (SPG8) is a pure hereditary spastic paraplegia characterized by slowly progressive spastic paraplegia of the lower limbs (i.e., hyperreflexia and clonus) with onset between ages 18 and 59 years (average: 37.2 years in one study). Other findings can include weakness with muscle wasting of the lower limbs, urinary urgency, and decreased vibration sense. Affected individuals often become wheelchair dependent. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1827]
Deafness and myopia (DFNMYP) syndrome is characterized by moderate-profound, bilateral, congenital or prelingual deafness (sensorineural hearing loss or auditory neuropathy spectrum disorder) and high myopia (>-6 diopters). In individuals with a molecularly confirmed diagnosis reported to date, hearing loss was progressive and severity ranged from moderate to profound. Vestibular testing was normal. Myopia was diagnosed at infancy or early childhood. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK269029]
Congenital Dyserythropoietic Anemia Type I
Congenital dyserythropoietic anemia type I (CDA I) is characterized by moderate to severe macrocytic anemia presenting occasionally in utero as severe anemia associated with hydrops fetalis but more commonly in neonates as hepatomegaly, early jaundice, and intrauterine growth retardation. Some cases present in childhood or adulthood. After the neonatal period, most affected individuals have lifelong moderate anemia, usually accompanied by jaundice and splenomegaly. Secondary hemochromatosis develops with age as a result of increased iron absorption even in those who are not transfused. Distal limb anomalies occur in 4%-14% of affected individuals. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK5313]
Autosomal Dominant Tubulointerstitial Kidney Disease, REN-Related
Familial juvenile hyperuricemic nephropathy type 2 (FJHN2) is characterized by hypoproliferative anemia with low hemoglobin concentrations found in most affected children by age one year; hyperuricemia and gout found in most (not all) affected individuals; and slowly progressive chronic tubulo-interstitial kidney disease. Some affected children have polyuria (excessive urine production leading to frequent urination) and enuresis. Mildly elevated serum creatinine concentration and reduced estimated glomerular filtration rate in an asymptomatic child often progresses to end-stage renal disease (ESRD) in the fourth to sixth decades of life. Of note, information on only four families with this condition has been published; better understanding of the disease is likely to emerge when more families are described. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK53700]
Dystonia/Parkinsonism, Hypermanganesemia, Polycythemia, and Chronic Liver Disease
The disorder dystonia/parkinsonism, hypermanganesemia, polycythemia, and chronic liver disease is characterized by the following:A movement disorder resulting from manganese accumulation in the basal ganglia Whole-blood manganese concentrations that often exceed 2000 nmol/L (normal: <320 nmol/L) Polycythemia Hepatomegaly with variable hepatic fibrosis/cirrhosis [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK100241]
Pallister-Hall syndrome (referred to as PHS in this entry) is characterized by a spectrum of anomalies ranging from polydactyly, asymptomatic bifid epiglottis, and hypothalamic hamartoma at the mild end to laryngotracheal cleft with neonatal lethality at the severe end. Individuals with mild PHS may be incorrectly diagnosed as having isolated postaxial polydactyly type A. Individuals with PHS can have pituitary insufficiency and may die as neonates from undiagnosed and untreated adrenal insufficiency. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1465]
Microcephaly-Capillary Malformation Syndrome
The microcephaly-capillary malformation (MIC-CAP) syndrome is characterized by microcephaly, generalized cutaneous capillary malformations (ranging from a few to hundreds of oval/circular macules or patches varying in size from 1-2 mm to several cm), hypoplastic distal phalanges of the hands and/or feet, intractable epilepsy, and profound developmental delay. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK174452]
ADCY5-related dyskinesia is characterized by infantile- to late-adolescent onset of paroxysmal choreiform, myoclonic, and/or dystonic movements that involve the limbs, neck, and/or face. Dyskinesias are often exacerbated by anxiety (although not by startle, caffeine, or alcohol). Facial ‘twitches” (previously thought to be myokymia) involving the periorbital and/or perioral muscles may also be present. Hypotonia and delayed motor milestones may be present in more severely affected infants. The movement disorder can be static or slowly progressive, with a tendency to stabilize in early middle age. Intellect and life span are normal. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK263441]
CHST3-related skeletal dysplasia is characterized by short stature of prenatal onset, joint dislocations (knees, hips, radial heads), club feet, and limitation of range of motion that can involve all large joints. Kyphosis and occasionally scoliosis with slight shortening of the trunk develop in childhood. Minor heart valve dysplasia has been described in several persons. Intellect, vision, and hearing are normal. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK62112]
The spectrum of ANO5-related muscle diseases is a continuum that ranges from asymptomatic hyperCKemia and exercise-induced myalgia to proximal and/or distal muscle weakness. The most typical presentation is limb-girdle muscular dystrophy type 2L (LGMD2L) with late-onset proximal lower-limb weakness (mean onset age 35 years; range 15-70 years). Less common is Miyoshi-like disease or Miyoshi muscular dystrophy 3 with early adult-onset calf distal myopathy (age 20 to 25 years). Incidental hyperCKemia may be present even earlier. Females have milder disease manifestations than males. Initial symptoms are walking difficulties, reduced sports performance, and difficulties in standing on toes as well as nonspecific exercise myalgia and/or burning sensation in the calf muscles. Muscle weakness and atrophy are frequently asymmetric. Bulbar or respiratory symptoms have not been reported. Disease progression is slow in both the LGMD and distal forms; ambulation is preserved until very late in the disease course. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK114459]
Emanuel syndrome is characterized by severe intellectual disability, microcephaly, failure to thrive, preauricular tags or pits, ear anomalies, cleft or high-arched palate, micrognathia, kidney abnormalities, congenital heart defects, and genital abnormalities in males. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1263]
Timothy syndrome is a multisystem disorder characterized by cardiac, hand/foot, facial, and neurodevelopmental features. Typical cardiac findings include a rate-corrected QT interval >480 ms, functional 2:1 AV block with bradycardia, tachyarrhythmias, and congenital heart defects (patent ductus arteriosus, patent foramen ovale, ventricular septal defect, tetralogy of Fallot, hypertrophic cardiomyopathy). The diagnosis of Timothy syndrome is generally made within the first few days of life although it may be suspected prenatally due to 2:1 AV block or bradycardia in the fetus. Hand/foot findings are unilateral or bilateral cutaneous syndactyly variably involving fingers two (index), three (middle), four (ring), and five (little) and bilateral cutaneous syndactyly of toes two and three. Facial findings include depressed nasal bridge, low-set ears, thin vermilion border of the upper lip, and round face. Neuropsychiatric involvement includes global developmental delays and autism spectrum disorders. Ventricular tachyarrhythmia is the leading cause of death, followed by infection and complications of intractable hypoglycemia. Average age of death is 2.5 years. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1403]
RRM2B-related mitochondrial disease can be grouped by disease pathogenesis, phenotype, and mode of inheritance into two major types: mitochondrial DNA (mtDNA) depletion and multiple mtDNA deletions. Mitochondrial DNA depletion usually manifests as severe multisystem disease (encephalomyopathy with proximal renal tubulopathy) and is often fatal in early life. Inheritance is autosomal recessive. Multiple mtDNA deletions cause tissue-specific cytochrome c oxidase (COX) deficiency. Inheritance can be either autosomal recessive (with progressive external ophthalmoplegia [PEO] and multisystem involvement manifesting during early childhood/adulthood) or autosomal dominant (with less severe, often tissue-specific manifestations [e.g., chronic PEO] developing in later adulthood). [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK195854]
Hypomyelination and congenital cataract (HCC) is usually characterized by bilateral congenital cataracts and normal psychomotor development in the first year of life, followed by slowly progressive neurologic impairment manifest as ataxia, spasticity (brisk tendon reflexes and bilateral extensor plantar responses), and mild to moderate cognitive impairment. Dysarthria and truncal hypotonia are observed. Cerebellar signs (truncal titubation and intention tremor) and peripheral neuropathy (muscle weakness and wasting of the legs) are present in the majority of affected individuals. Seizures can occur. In a few cases cataracts may be absent. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK2587]
Congenital Deafness with Labyrinthine Aplasia, Microtia, and Microdontia
Congenital deafness with labyrinthine aplasia, microtia, and microdontia (LAMM syndrome) is characterized by: profound bilateral congenital sensorineural deafness associated with inner ear anomalies (most often bilateral complete labyrinthine aplasia); microtia (type I) that is typically bilateral (although unilateral microtia and normal external ears are observed on occasion); and microdontia (small teeth). Individuals with LAMM syndrome commonly have motor delays during infancy presumably due to impaired balance from inner ear (vestibular) abnormalities. Growth, physical development, and cognition are normal. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK100664]
Char syndrome is characterized by the triad of typical facial features, patent ductus arteriosus (PDA), and aplasia or hypoplasia of the middle phalanges of the fifth fingers. Typical facial features are flat midface, flat nasal bridge and broad flat nasal tip, wide-set eyes, downslanting palpebral fissures, mild ptosis, short philtrum resulting in a triangular mouth, and thickened (patulous) everted lips. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1106]
Oculocutaneous albinism type 1 (OCA1) is characterized by hypopigmentation of the skin and hair and the distinctive ocular changes found in all types of albinism, including: nystagmus; reduced iris pigment with iris translucency; reduced retinal pigment with visualization of the choroidal blood vessels on ophthalmoscopic examination; foveal hypoplasia with substantial reduction in visual acuity, usually in the range of 20/100 to 20/400; and misrouting of the optic nerve fiber radiations at the chiasm, resulting in strabismus, reduced stereoscopic vision, and altered visually evoked potentials (VEP). Individuals with OCA1A have white hair, white skin that does not tan, and fully translucent irides, none of which darken with age. At birth, individuals with OCA1B have white or very light yellow hair that darkens minimally with age, white skin that over time develops some minimal generalized pigment and may tan slightly with judicious sun exposure, and blue irides that darken to green/hazel or light brown/tan with age, although transillumination defects persist. Visual acuity may be 20/60 or better in some eyes. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1166]
Troyer syndrome is characterized by progressive spastic paraparesis, dysarthria, and pseudobulbar palsy; distal amyotrophy; motor and cognitive delays; short stature; and subtle skeletal abnormalities. Most affected children exhibit delays in walking and talking followed by slow deterioration in both gait and speech. Emotional lability and affective disorders, such as inappropriate euphoria and/or crying, are common. Mild cerebellar signs are common. The most severely affected individuals have choreoathetosis. Life expectancy is normal. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1382]
Bloom’s syndrome (BSyn) is characterized by severe pre- and postnatal growth deficiency, highly characteristic sparseness of subcutaneous fat tissue throughout infancy and early childhood, and short stature throughout postnatal life that in most affected individuals is accompanied by an erythematous and sun-sensitive skin lesion of the face. Gastroesophageal reflux (GER) is common and very possibly responsible for infections of the upper respiratory tract, the middle ear, and the lung that occur repeatedly in most persons with BSyn. Although most affected individuals have normal intellectual ability, many exhibit a poorly defined (and little studied) learning disability. Women may be fertile, but menopause occurs unusually early; men are infertile. Serious medical complications that are much more common than in the general population and that also appear at unusually early ages are chronic obstructive pulmonary disease, diabetes mellitus resembling the adult-onset type, and cancer of a wide variety of types and anatomic sites. BSyn is very rare in all national and ethnic groups but is relatively less rare in Ashkenazi Jews. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1398]
3-M syndrome is characterized by severe pre- and postnatal growth retardation (final height 5-6 SD below the mean; i.e., 120-130 cm), characteristic facies, and normal intelligence. Additional features of 3-M syndrome include short broad neck, prominent trapezii, deformed sternum, short thorax, square shoulders, winged scapulae, hyperlordosis, short fifth fingers, prominent heels, and loose joints. Males with 3-M syndrome have hypogonadism and, occasionally, hypospadias. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1481]
X-linked Charcot-Marie-Tooth neuropathy type 5 (CMTX5), part of the spectrum of PRPS1-related disorders, is characterized by peripheral neuropathy, early-onset (prelingual) bilateral profound sensorineural hearing loss, and optic neuropathy. The onset of peripheral neuropathy is between ages five and 12 years. The lower extremities are affected earlier and more severely than upper extremities. Initial manifestations often include foot drop or gait disturbance. Onset of visual impairment is between ages seven and 20 years. Intellect and life span are normal. Carrier females do not have findings of CMTX5. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1876]
Spinocerebellar ataxia type 28 (SCA28) is characterized by young-adult onset, slowly progressive gait and limb ataxia, dysarthria, hyperreflexia of the lower limbs, nystagmus, and ophthalmoparesis. The usual age at onset is early adulthood (24.4 ± 14.9 years); range is from age three to 60 years. The course of the disease is slowly progressive without impairment of functional autonomy even decades after onset. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK54582]
Neuroferritinopathy typically presents with progressive adult-onset chorea or dystonia affecting one or two limbs, and subtle cognitive deficits. The movement disorder involves additional limbs within five to ten years and becomes more generalized within 20 years. When present, asymmetry remains throughout the course of the disorder. The majority of individuals develop a characteristic orofacial action-specific dystonia related to speech that leads to dysarthrophonia. Frontalis overactivity and orolingual dyskinesia are common. Cognitive deficits and behavioral issues become major problems with time. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1141]
IMAGe syndrome is an acronym for the major findings of intrauterine growth restriction (IUGR), metaphyseal dysplasia, adrenal hypoplasia congenita (AHC), and genitourinary abnormalities (in males). All 25 individuals with a clinical and/or molecular diagnosis reported to date have had: IUGR; Some sort of skeletal abnormality (most commonly delayed bone age and short stature and, occasionally, metaphyseal and epiphyseal dysplasia of varying severity); Adrenal insufficiency typically presenting in the first month of life as an adrenal crisis or rarely later in childhood with failure to thrive and recurrent vomiting; and Genital abnormalities in males (cryptorchidism, micropenis, and hypospadias) but not in females. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK190103]
Phosphoribosylpyrophosphate Synthetase Superactivity
Phosphoribosylpyrophosphate synthetase (PRS) superactivity is characterized by hyperuricemia and hyperuricosuria and is divided into a severe phenotype with infantile or early-childhood onset and a milder phenotype with late-juvenile or early-adult onset. Variable combinations of sensorineural hearing loss, hypotonia, and ataxia observed in the severe type are not usually present in the mild type. In the mild type, uric acid crystalluria or a urinary stone is commonly the first clinical finding, followed later by gouty arthritis if serum urate concentration is not controlled. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1973]
EXOSC3-Related Pontocerebellar Hypoplasia
EXOSC3-related pontocerebellar hypoplasia (PCH) is characterized by abnormalities in the posterior fossa and degeneration of the anterior horn cells. At birth, skeletal muscle weakness manifests as hypotonia (sometimes with congenital joint contractures) and poor feeding. In persons with prolonged survival, spasticity, dystonia, and seizures become evident. Within the first year of life respiratory insufficiency and swallowing difficulties are common. Intellectual disability is severe. Life expectancy ranges from a few weeks to adolescence. To date, 51 individuals with PCH from 36 families with mutation of EXOSC3 have been described. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK236968]
The spectrum of ADAMTSL4-related eye disorders is a continuum that includes the phenotypes known as ‘autosomal recessive isolated ectopia lentis’ and ‘ectopia lentis et pupillae’ as well as more minor eye anomalies with no displacement of the pupil and very mild displacement of the lens; no systemic abnormalities are observed. Typical eye findings are dislocation of the lens, congenital abnormalities of the iris, refractive errors that may lead to amblyopia, and early-onset cataract. Increased intraocular pressure and retinal detachment may occur on occasion. Eye findings can vary within a family and between the eyes in an individual. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK84111]
BSCL2-Related Neurologic Disorders/Seipinopathy
The spectrum of BSCL2-related neurologic disorders includes Silver syndrome and variants of Charcot-Marie-Tooth disease type 2, distal hereditary motor neuropathy (dHMN) type V, and spastic paraplegia 17. Features of these disorders include onset of symptoms ranging from the first to the seventh decade, slow disease progression, upper motor neuron involvement (gait disturbance with pyramidal signs ranging from mild to severe spasticity with hyperreflexia in the lower limbs and variable extensor plantar responses), lower motor neuron involvement (amyotrophy of the peroneal muscles and small muscles of the hand), abnormal vibration sense, and pes cavus and other foot deformities. Disease severity is variable among and within families. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1307]
Polymicrogyria is characterized by stable neurologic deficits, i.e., a "static encephalopathy." The mildest form, unilateral focal polymicrogyria, may have minimal neurologic manifestations. In more severe forms, focal, motor, sensory, visual, or cognitive problems may be present, depending on the brain region affected. In the most widespread form, bilateral generalized polymicrogyria, severe intellectual disability, cerebral palsy, and refractory epilepsy may be present. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1329]
Multiple Cutaneous and Mucosal Venous Malformations
The condition multiple cutaneous and mucosal venous malformations (VMCM) is characterized by the presence of small, multifocal bluish cutaneous and/or mucosal venous malformations. They are usually present at birth. New lesions appear with time. Small lesions are usually asymptomatic; larger lesions can invade subcutaneous muscle and cause pain. Malignant transformation has not been reported. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1967]
Thrombocytopenia absent radius (TAR) syndrome is characterized by bilateral absence of the radii with the presence of both thumbs and thrombocytopenia (<50 platelets/nL) that is generally transient. Thrombocytopenia may be congenital or may develop within the first few weeks to months of life; in general, thrombocytopenic episodes decrease with age. Cow’s milk allergy is common and can be associated with exacerbation of thrombocytopenia. Other anomalies of the skeleton (upper and lower limbs, ribs, and vertebrae), heart, and genitourinary system (renal anomalies and agenesis of uterus, cervix, and upper part of the vagina) can occur. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK23758]
Autosomal dominant Robinow syndrome (ADRS) is characterized by skeletal findings (short stature, mesomelic limb shortening predominantly of the upper limbs, and brachydactyly); genital abnormalities (in males: micropenis/webbed penis, hypoplastic scrotum, cryptorchidism; in females: hypoplastic clitoris and labia majora); dysmorphic facial features; dental abnormalities (including malocclusion, crowding, hypodontia, late eruption of permanent teeth); bilobed tongue; occasional prenatal macrocephaly with postnatal decrease in head circumference. Less common findings include renal anomalies, radial head dislocation, vertebral abnormalities such as hemivertebrae and scoliosis, nail dysplasia, cardiac defect, cleft lip/palate, and (rarely) cognitive delay. When present, cardiac defects are a major cause of morbidity and mortality. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK268648]
Kleefstra syndrome is characterized by intellectual disability, childhood hypotonia, and distinctive facial features. The majority of individuals function in the moderate to severe spectrum of intellectual disability although a few individuals have mild delay and total IQ around 70. Although most have severe expressive speech delay with little speech development, general language development is usually at a higher level, making nonverbal communication possible. A complex pattern of other findings can also be observed including heart defects, renal/urologic defects, genital defects in males, severe respiratory infections, epilepsy/febrile seizures, autistic-like features in childhood, and extreme apathy or catatonic-like features after puberty. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK47079]
MPV17-Related Hepatocerebral Mitochondrial DNA Maintenance Defect
MPV17-related hepatocerebral mitochondrial DNA (mtDNA) depletion syndrome is characterized by infantile-onset liver dysfunction that typically progresses to liver failure; neurologic involvement (developmental delay, hypotonia, and muscle weakness in the majority; ataxia, seizures, and motor and sensory peripheral neuropathy in some); failure to thrive; and metabolic derangements including lactic acidosis and hypoglycemic crises. Less frequent manifestations include renal tubulopathy, hypoparathyroidism, gastrointestinal dysmotility, and corneal anesthesia. Progressive liver disease often leads to death in infancy or early childhood. Hepatocellular carcinoma has been reported. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK92947]
Nail-patella syndrome (NPS) involves a classic clinical tetrad of changes in the nails, knees, and elbows, and the presence of iliac horns. Nail changes are the most constant feature of NPS. Nails may be absent, hypoplastic, or dystrophic; ridged longitudinally or horizontally; pitted; discolored; separated into two halves by a longitudinal cleft or ridge of skin; and thin or (less often) thickened. The patellae may be small, irregularly shaped, or absent. Elbow abnormalities may include limitation of extension, pronation, and supination; cubitus valgus; and antecubital pterygia. Iliac horns are bilateral, conical, bony processes that project posteriorly and laterally from the central part of the iliac bones of the pelvis. Renal involvement, first manifest as proteinuria with or without hematuria, occurs in 30%-50% of affected individuals; end-stage renal disease (ESRD) occurs in about 5% of affected individuals. Primary open-angle glaucoma and ocular hypertension occur at increased frequency and at a younger age than in the general population. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1132]
TK2-Related Mitochondrial DNA Maintenance Defect, Myopathic Form
TK2-related mitochondrial DNA (mtDNA) depletion syndrome is a phenotypic continuum that ranges from severe to mild. To date, approximately 45 individuals with a molecularly confirmed diagnosis have been reported. Rapidly progressive proximal muscle weakness in newborns with encephalopathy, epilepsy, and early death; A spinal muscular atrophy-like presentation; Progressive myopathy with dystrophic changes (including sensorineural hearing loss); Hepatomegaly with elevated liver enzymes associated with the severe early-onset myopathy. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK114628]
Hepatic Veno-Occlusive Disease with Immunodeficiency
Hepatic veno-occlusive disease with immunodeficiency (VODI) is characterized by (1) primary immunodeficiency and (2) terminal hepatic lobular vascular occlusion and hepatic fibrosis manifest as hepatomegaly and/or hepatic failure. Onset is usually before age six months. The immunodeficiency comprises severe hypogammaglobulinemia, clinical evidence of T-cell immunodeficiency with normal numbers of circulating T cells, absent lymph node germinal centers, and absent tissue plasma cells. Bacterial and opportunistic infections including Pneumocystis jirovecii infection, mucocutaneous candidiasis, and enteroviral or cytomegalovirus infections occur. In the past the prognosis for affected individuals was poor, with 100% mortality in the first year of life if unrecognized and untreated with intravenous immunoglobulin (IVIG) and Pneumocystis jirovecii prophylaxis. However, with early recognition and treatment there is a marked improvement in prognosis. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1271]
Shprintzen-Goldberg syndrome (SGS) is characterized by: craniosynostosis of the coronal, sagittal, or lambdoid sutures; dolichocephaly; distinctive craniofacial features; skeletal changes (dolichostenomelia, arachnodactyly, camptodactyly, pes planus, pectus excavatum or carinatum, scoliosis, joint hypermobility or contractures and C1/C2 spine malformation); neurologic abnormalities; intellectual disability; and brain anomalies (hydrocephalus, dilatation of the lateral ventricles, and Chiari 1 malformation). Cardiovascular anomalies may include mitral valve prolapse, mitral regurgitation/incompetence, aortic regurgitation and aortic root dilatation. Minimal subcutaneous fat, abdominal wall defects, myopia, and cryptorchidism in males, are also characteristic findings. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1277]
SPTLC1-Related Hereditary Sensory Neuropathy
Hereditary sensory neuropathy type IA (HSN1A) is an axonal form of hereditary motor and sensory neuropathy distinguished by prominent early sensory loss and later positive sensory phenomena including dysesthesia and characteristic "lightning" or "shooting" pains. Loss of sensation can lead to painless injuries, which, if unrecognized, result in slow wound healing and subsequent osteomyelitis requiring distal amputations. HSN1A is often associated with progressive sensorineural deafness. Motor involvement is present in all advanced cases and can be severe. After age 20 years, the distal wasting and weakness may involve proximal muscles so that a person in his/her 60s or 70s may require a wheelchair for mobility. Drenching sweating of the hands and feet is sometimes reported and occasionally pupillary abnormalities are observed; however, visceral signs of autonomic involvement are rare. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1390]
Laing distal myopathy is characterized by early-onset weakness (usually before age 5 years) that initially involves the dorsiflexors of the ankles and great toes and then the finger extensors, especially those of the third and fourth fingers. Weakness of the neck flexors is seen in most affected individuals and mild facial weakness is often present. After distal weakness has been present for more than ten years, mild proximal weakness may be observed. Life expectancy is normal. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1433]
Typical Greig cephalopolysyndactyly syndrome (GCPS) is characterized by preaxial polydactyly or mixed pre- and postaxial polydactyly, true widely spaced eyes, and macrocephaly. Individuals with mild GCPS may have subtle craniofacial findings. The mild end of the GCPS spectrum is a continuum with preaxial polysyndactyly type IV and crossed polydactyly (preaxial polydactyly of the feet and postaxial polydactyly of the hands plus syndactyly of fingers 3-4 and toes 1-3). Individuals with severe GCPS can have seizures, hydrocephalus, and intellectual disability. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1446]
CLCN2-related leukoencephalopathy (CC2L) is characterized by nonspecific neurologic findings, mild visual impairment from chorioretinopathy or optic atrophy, male infertility, and characteristic findings on brain MRI. Neurologic findings include mild ataxia (action tremor and gait instability following initially normal motor development; occasionally mild spasticity), learning disabilities in some (ranging from mild to severe cognitive impairment), and headaches in some (usually intermittent, severe, and diffuse). Affected individuals remain ambulatory and do not require support for walking, and none has become blind. To date CC2L has been reported or identified in 16 individuals from 15 families. It is not yet known if the findings occurring in single individuals (i.e., vertigo, tinnitus, and progressive hearing loss; psychiatric symptoms; and paroxysmal kinesigenic dyskinesia) are part of the phenotypic spectrum or unrelated findings. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK326661]
Snyder-Robinson syndrome (SRS) is an X-linked intellectual disability syndrome characterized by asthenic build, facial dysmorphism with a prominent lower lip, kyphoscoliosis, osteoporosis, and speech abnormalities. Developmental delay usually presents as failure to meet early developmental milestones and then evolves to moderate to profound global intellectual disability (which appears to remain stable over time) and variable motor disability. Asthenic habitus and low muscle mass usually develop during the first year, even in males who are ambulatory. During the first decade, males with SRS develop osteoporosis, resulting in fractures in the absence of trauma. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK144284]
Peters plus syndrome is characterized by anterior chamber eye anomalies, short limbs with broad distal extremities, variable developmental delay/intellectual disability, characteristic facial features, and cleft lip/palate. The most common anterior chamber defect is Peters' anomaly, consisting of central corneal clouding, thinning of the posterior cornea, and iridocorneal adhesions. Cataracts and glaucoma are common. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1464]
Carnitine Palmitoyltransferase 1A Deficiency
Carnitine palmitoyltransferase 1A (CPT1A) deficiency is a disorder of long-chain fatty acid oxidation. Clinical symptoms usually occur in an individual with a concurrent febrile or gastrointestinal illness when energy demands are increased; onset of symptoms is usually rapid. The three recognized phenotypes are hepatic encephalopathy, in which individuals (typically children) present with hypoketotic hypoglycemia and sudden onset of liver failure; adult-onset myopathy, seen in one individual of Inuit origin; and acute fatty liver of pregnancy, in which the fetus is homozygous for a pathogenic variant in CPT1A that causes CPT1A deficiency. Between episodes of hepatic encephalopathy, individuals appear developmentally and cognitively normal unless previous metabolic decompensation has resulted in neurologic damage. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1527]
VLDLR-associated cerebellar hypoplasia (VLDLR-CH) is characterized by non-progressive congenital ataxia that is predominantly truncal and results in delayed ambulation, moderate-to-profound intellectual disability, dysarthria, strabismus, and seizures. Children either learn to walk very late (often after age 6 years) or never achieve independent ambulation. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1874]
Donnai-Barrow syndrome (DBS) is characterized by typical craniofacial features (ocular hypertelorism, enlarged fontanelle), ocular findings (high myopia, retinal detachment, progressive vision loss, and iris coloboma), sensorineural hearing loss, agenesis of the corpus callosum, intellectual disability, and congenital diaphragmatic hernia (CDH) and/or omphalocele. Both inter- and intrafamilial phenotypic variability are observed. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1878]
Perry syndrome is characterized by parkinsonism, hypoventilation, depression, and weight loss. The mean age at onset is 48 years; the mean disease duration is five years. Parkinsonism and psychiatric changes (depression, apathy, character changes, and withdrawal) tend to occur early; severe weight loss and hypoventilation manifest later. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK47027]
CEBPA-Associated Familial Acute Myeloid Leukemia (AML)
Familial acute myeloid leukemia (AML) with mutated CEBPA is defined as AML in which a germline CEBPA pathogenic variant is present in a family in which multiple individuals have AML. In contrast, sporadic AML with mutated CEBPA is defined as AML in which a CEBPA pathogenic variant is identified in somatic (i.e., leukemic) cells but not in germline (i.e., non-leukemic) cells. Too few persons with familial AML with mutated CEBPA have been reported to be certain about the natural history of the disease. The age of onset of familial AML with mutated CEBPA appears to be earlier than sporadic AML; disease onset has been reported in persons as young as age four years and older than age 50 years. The prognosis of individuals with familial AML with mutated CEBPA appears to be favorable (~50%-65% overall survival) compared to the ~25%-40% overall survival of those who have normal karyotype AML but no germline CEPBA pathogenic variant. Individuals with familial AML with mutated CEBPA who have been cured of their initial disease may be at greater risk of developing additional malignant clones than persons with sporadic disease. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK47457]
Myopathy with deficiency of ISCU, a mitochondrial myopathy, is characterized by lifelong exercise intolerance in which minor exertion causes tachycardia, shortness of breath, and fatigue and pain of active muscles; episodes of more profound exercise intolerance associated with rhabdomyolysis, myoglobinuria, and weakness that may be severe; and typically full recovery of muscle strength between episodes of rhabdomyolysis. Affected individuals usually have near-normal strength; they can have large calves. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK5299]
Adult polyglucosan body disease (APBD) is characterized by adult-onset progressive neurogenic bladder, gait difficulties (i.e., spasticity and weakness) from mixed upper and lower motor neuron involvement, sensory loss predominantly in the distal lower extremities, and mild cognitive difficulties (often executive dysfunction). [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK5300]
The spectrum of COL4A1-related disorders includes: small-vessel brain disease of varying severity variably associated with porencephaly, cerebral aneurysms, eye defects (retinal arterial tortuosity, Axenfeld-Rieger anomaly, cataract) and systemic findings (kidney involvement, muscle cramps, Raynaud phenomenon, and cardiac arrhythmia). On imaging studies, small-vessel brain disease is manifest as diffuse periventricular leukoencephalopathy, lacunar infarcts, microhemorrhage, dilated perivascular spaces, and deep intracerebral hemorrhages. Clinically, small-vessel brain disease manifests as infantile hemiparesis, seizures, single or recurrent hemorrhagic stroke, ischemic stroke, and isolated migraine with aura. Porencephaly (fluid-filled cavities in the brain detected by CT or MRI) is typically manifest as infantile hemiparesis, seizures, and intellectual disability; however, on occasion it can be an incidental finding. Hereditary angiopathy with nephropathy, aneurysms, and muscle cramps (HANAC) syndrome usually associates asymptomatic small-vessel brain disease, cerebral large vessel involvement (i.e., aneurysms), and systemic findings involving the kidney, muscle, and small vessels of the eye. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK7046]
Salih myopathy is characterized by muscle weakness (manifest during the neonatal period or in early infancy) and delayed motor development; children acquire independent walking between age 20 months and four years. In the first decade of life, global motor performances are stable or tend to improve. Moderate joint and neck contractures and spinal rigidity may start in the first decade but become more obvious in the second decade. Scoliosis develops after age 11 years. Cardiac dysfunction starts between ages five and 16 years, progresses rapidly, and leads to death between ages eight and 20 years, usually from heart rhythm disturbances. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK83297]
Variegate porphyria (VP) is a cutaneous porphyria (with chronic blistering skin lesions) and an acute porphyria (with severe episodic neurovisceral symptoms). The most common manifestation of VP is adult-onset cutaneous blistering lesions (subepidermal vesicles, bullae, and erosions that crust over and heal slowly) of sun-exposed skin, especially the hands and face. Other chronic skin findings include milia, scarring, thickening, and areas of decreased and increased skin pigmentation. Facial hyperpigmentation and hypertrichosis may occur. Cutaneous manifestations may improve in winter, and be less prevalent in northern regions and in dark-skinned individuals. Acute neurovisceral symptoms can occur any time after puberty, but less often in the elderly. Acute manifestations are highly variable, but may be similar from episode to episode in a patient with recurrent attacks; not all symptoms are present in a single episode; and acute symptoms may become chronic. Symptoms are more common in women than men. The most common symptoms are abdominal pain; constipation; pain in the back, chest, and extremities; anxiety; seizures; and a primarily motor neuropathy resulting in muscle weakness that may progress to quadriparesis and respiratory paralysis. Psychiatric disturbances and autonomic neuropathy can also be observed. Acute attacks may be severe and are potentially fatal. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK121283]
GARS-associated axonal neuropathy (Charcot-Marie-Tooth neuropathy type 2D/distal spinal muscular atrophy V [CMT2D/dSMA-V]) is characterized by adolescent or early-adult onset of bilateral weakness and atrophy of thenar and first dorsal interosseus muscles, sparing of the hypothenar eminence until later in the course of illness, and mild to moderate impairment of vibration sense in the hands and feet later in the disease course in a minority of individuals. The phenotype is considered the CMT2D subtype when sensory deficits (reduction of pinprick, temperature, touch, and vibration perception in a stocking and [less often] glove pattern) are present and dSMA-V when sensory deficits are absent. The lower limbs are involved in about half of affected individuals. The earliest elicited manifestations in many individuals are transient cramping and pain in the hands on exposure to cold and cramping in calf muscles on exertion. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1242]
OPA3-Related 3-Methylglutaconic Aciduria
OPA3-related 3-methylglutaconic aciduria is characterized by optic atrophy and/or choreoathetoid movement disorder with onset before age ten years. Optic atrophy is associated with progressive, decreased visual acuity within the first years of life, sometimes associated with infantile-onset horizontal nystagmus. Most individuals have chorea, often severe enough to restrict ambulation. Some are confined to a wheelchair from an early age. Although most individuals develop spastic paraparesis, mild ataxia, and occasional mild cognitive deficit in their second decade, the course of the disease is relatively stable. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1473]
EZH2-related overgrowth includes EZH2-related Weaver syndrome at one end of the spectrum and tall stature at the other. Although most individuals diagnosed with a heterozygous EZH2 pathogenic variant have been identified because of a clinical suspicion of Weaver syndrome, a minority have been identified through molecular genetic testing of family members of probands or individuals with overgrowth who did not have a clinical diagnosis of Weaver syndrome. Thus, the extent of the phenotypic spectrum associated with a heterozygous EZH2 pathogenic variant is not yet known. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK148820]
Huntington disease-like 2 (HDL2) typically presents in midlife with a relentless progressive triad of movement, emotional, and cognitive abnormalities progressing to death over ten to 20 years. In some individuals the presentation resembles juvenile-onset Huntington disease (HD) or the Westphal variant of HD, usually presenting in the fourth decade (ages 29 to 41 years) with diminished coordination and weight loss despite increase in food intake. Neurologic abnormalities include parkinsonism (rigidity, bradykinesia, tremor), dysarthria, and hyperreflexia. In others the presentation is more variable but, in general, corresponds to typical HD. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1529]
Nonsyndromic Disorders of Testicular Development
46,XY disorder of sex development (46,XY DSD) is characterized by a 46,XY karyotype, ambiguous genitalia with mild to severe penoscrotal hypospadias with or without chordee, dysgenetic testes, reduced to no sperm production, and müllerian structures that range from absent to presence of a fully developed uterus and fallopian tubes. 46,XY complete gonadal dysgenesis (46,XY CGD) is characterized by a 46,XY karyotype, normal female external genitalia, completely undeveloped (”streak”) gonads, no sperm production, and presence of normal müllerian structures. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1547]
SHORT syndrome is a mnemonic for short stature, hyperextensibility, ocular depression (deeply set eyes), Rieger anomaly, and teething delay. It is now recognized that the features most consistently observed in SHORT syndrome are mild intrauterine growth restriction (IUGR); mild short stature; partial lipodystrophy (evident at birth in the face, and later in the chest and upper extremities, often sparing the buttocks and legs); and a characteristic facial gestalt. Other frequent features include: Axenfeld-Rieger anomaly or related ocular anterior chamber dysgenesis; delayed dentition and a variety of dental abnormalities; insulin resistance (typically in mid-childhood to adolescence) and/or diabetes mellitus in early adulthood; and sensorineural hearing loss. To date the diagnosis has been molecularly confirmed in individuals from 16 families; thus, the current understanding of the phenotypic spectrum and natural history are likely to evolve over time. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK201365]
Perrault syndrome is characterized by sensorineural hearing loss (SNHL) in males and females, and ovarian dysfunction in females. The SNHL is bilateral and ranges in severity from moderate with early-childhood onset to profound with prelingual (congenital) onset to moderate with early-childhood onset. When onset is in early childhood, hearing loss can be progressive. Ovarian dysfunction ranges from gonadal dysgenesis (absent or streak gonads) manifesting as primary amenorrhea to primary ovarian insufficiency (POI) defined as cessation of menses before age 40 years. Fertility in affected males is reported as normal (although the number of reported males is limited). Neurologic features described in some affected women include developmental delay or intellectual disability, cerebellar ataxia, and motor and sensory peripheral neuropathy. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK242617]
Infants with Duarte variant galactosemia who are on breast milk or a lactose-containing formula are typically, but not always, asymptomatic. Abnormalities, such as jaundice, which may be seen in some infants, resolve rapidly when the baby is switched to a low-galactose formula. Many healthcare professionals believe that Duarte variant galactosemia does not result in clinical disease either with or without dietary intervention; however, there are also reports to the contrary and no adequately powered study either confirming or refuting this assumption has been reported. Because available data about the neurodevelopmental outcomes of children with Duarte variant galactosemia are conflicting, further studies are warranted to determine what long-term outcomes are and whether the dietary intake of galactose in the first year of life influences outcome. Premature ovarian insufficiency has not been reported for girls or women with Duarte variant galactosemia. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK258640]
16p12.2 microdeletion is characterized by variable clinical findings that do not constitute a recognizable syndrome. Of note, the significant bias in ascertainment of individuals undergoing clinical chromosomal microarray analysis (i.e., children with intellectual disability and developmental delay; individuals with schizophrenia) makes it difficult to accurately associate specific phenotypes to the 16p12.2 microdeletion. Findings commonly observed in children (probands) with this deletion include: developmental delay, cognitive impairment (ranges from mild to profound), growth impairment (including short stature), cardiac malformations, epilepsy, and psychiatric and/or behavioral problems. Other findings can include: hearing loss, dental abnormalities, renal and genital anomalies (the latter in males), and cleft palate ± cleft lip. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK274565]
EFEMP2-related cutis laxa, or autosomal recessive cutis laxa type 1B (ARCL1B), is characterized by cutis laxa and systemic involvement, most commonly arterial tortuosity, aneurysms, and stenosis; retrognathia; joint laxity; and arachnodactyly. Severity ranges from perinatal lethality as a result of cardiopulmonary failure to manifestations limited to the vascular and craniofacial systems. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK54467]
Pyruvate carboxylase (PC) deficiency is characterized in most affected individuals by failure to thrive, developmental delay, recurrent seizures, and metabolic acidosis. Three clinical types are recognized: type A (infantile form), in which most affected children die in infancy or early childhood; type B (severe neonatal form), in which affected infants have hepatomegaly, pyramidal tract signs, and abnormal movement and die within the first three months of life; and type C (intermittent/benign form), in which affected individuals have normal or mildly delayed neurologic development and episodic metabolic acidosis. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK6852]
Proteus syndrome is characterized by progressive, segmental or patchy overgrowth of diverse tissues of all germ layers, most commonly affecting the skeleton, skin, and adipose and central nervous systems. In most individuals Proteus syndrome has minimal or no manifestations at birth, develops and progresses rapidly beginning in the toddler period, and relentlessly progresses through childhood, causing severe overgrowth and disfigurement. It is associated with a range of tumors, pulmonary complications, and a striking predisposition to deep vein thrombosis and pulmonary embolism. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK99495]
X-linked protoporphyria (XLP) is characterized in affected males by cutaneous photosensitivity (usually beginning in infancy or childhood) that results in tingling, burning, pain, and itching within minutes of sun/light exposure and may be accompanied by swelling and redness. Vesicular lesions are uncommon. Pain, which may seem out of proportion to the visible skin lesions, may persist for hours or days after the initial phototoxic reaction. Photosensitivity usually remains for life. Multiple episodes of acute photosensitivity may lead to chronic changes of sun-exposed skin (lichenification, leathery pseudovesicles, grooving around the lips) and loss of lunulae of the nails. An unknown proportion of individuals with XLP develop liver disease. Except for those with advanced liver disease, life expectancy is not reduced. The phenotype in heterozygous females ranges from asymptomatic to as severe as affected males. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK121284]
Hexosaminidase A deficiency results in a group of neurodegenerative disorders caused by intralysosomal storage of the specific glycosphingolipid, GM2 ganglioside. The prototype hexosaminidase A deficiency is Tay-Sachs disease, also known as the acute infantile variant. Tay-Sachs disease is characterized by progressive weakness, loss of motor skills, decreased attentiveness, and increased startle response beginning between ages three and six months with progressive evidence of neurodegeneration including: seizures, blindness, spasticity, eventual total incapacitation, and death, usually before age four years. The juvenile (subacute), chronic, and adult-onset variants of hexosaminidase A deficiency have later onsets, slower progression, and more variable neurologic findings, including: progressive dystonia, spinocerebellar degeneration, motor neuron disease, and, in some individuals with adult-onset disease, a bipolar form of psychosis. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1218]
Rhizomelic Chondrodysplasia Punctata Type 1
Rhizomelic chondrodysplasia punctata type 1 (RCDP1) classic type, a peroxisome biogenesis disorder (PBD), is characterized by proximal shortening of the humerus and to a lesser degree the femur (rhizomelia), punctate calcifications in cartilage with epiphyseal and metaphyseal abnormalities (chondrodysplasia punctata, or CDP), coronal clefts of the vertebral bodies, and cataracts that are usually present at birth or appear in the first few months of life. Birth weight, length, and head circumference are often at the lower range of normal; postnatal growth deficiency is profound. Intellectual disability is severe, and the majority of children develop seizures. Most affected children do not survive the first decade of life; a proportion die in the neonatal period. A milder phenotype in which all affected individuals have congenital cataracts and chondrodysplasia is now recognized; some do not have rhizomelia, and some have less severe intellectual disability and growth deficiency. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1270]
Leukoencephalopathy with Brain Stem and Spinal Cord Involvement and Lactate Elevation
Leukoencephalopathy with brain stem and spinal cord involvement and lactate elevation (LBSL) is characterized by slowly progressive cerebellar ataxia and spasticity with dorsal column dysfunction (decreased position and vibration sense) in most patients. The neurologic dysfunction involves the legs more than the arms. The tendon reflexes are retained. Deterioration of motor skills usually starts in childhood or adolescence, but occasionally not until adulthood. Dysarthria develops over time. Occasional findings include: epilepsy; learning problems; cognitive decline; and reduced consciousness, neurologic deterioration, and fever following minor head trauma. Many affected individuals become wheelchair dependent in their teens or twenties. Neonatal or early-infantile onset patients have a severe disease course and may die, whereas late-infantile and early-childhood onset is associated with early wheelchair dependency. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK43417]
Epimerase deficiency galactosemia (GALE deficiency galactosemia) is a continuum comprising three forms: Generalized. Enzyme activity is profoundly decreased in all tissues tested. Peripheral. Enzyme activity is deficient in red blood cells and circulating white blood cells, but normal or near normal in all other tissues. Intermediate. Enzyme activity is deficient in red blood cells and circulating white blood cells and less than 50% of normal levels in other cells tested. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK51671]
Esophageal Atresia/Tracheoesophageal Fistula Overview
Esophageal atresia (EA) is a developmental defect of the upper gastrointestinal tract in which the continuity between the upper and lower esophagus is lost. EA can occur with or without tracheoesophageal fistula (TEF), an abnormal connection between the trachea and the esophagus. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK5192]
TSEN54-Related Pontocerebellar Hypoplasia
TSEN54-related pontocerebellar hypoplasia (PCH) includes three PCH types (PCH2, 4, and 5) that share characteristic neuroradiologic and neurologic findings. The three types (which differ mainly in life expectancy) were thought to be distinct entities before their molecular basis was known. Children with PCH2 usually succumb before age ten years, whereas those with PCH4 and 5 usually succumb as neonates. Children with PCH2 have generalized clonus, incoordination of sucking and swallowing, impaired motor and cognitive development with lack of voluntary motor development, central visual impairment, and an increased risk for malignant hyperthermia. Epilepsy is present in approximately 50%. Neonates with PCH4 often have seizures, multiple joint contractures (''arthrogryposis''), generalized clonus, and central respiratory impairment. PCH5, which resembles PCH4, has been described in one family. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK9673]
Mitochondrial DNA (mtDNA) deletion syndromes predominantly comprise three overlapping phenotypes that are usually simplex (i.e., a single occurrence in a family), but rarely may be observed in different members of the same family or may evolve in a given individual over time. The three phenotypes are Kearns-Sayre syndrome (KSS), Pearson syndrome, and progressive external ophthalmoplegia (PEO). Rarely Leigh syndrome can be a manifestation of a mtDNA deletion. KSS is a multisystem disorder defined by the triad of onset before age 20 years, pigmentary retinopathy, and PEO. In addition, affected individuals have at least one of the following: cardiac conduction block, cerebrospinal fluid protein concentration greater than 100 mg/dL, or cerebellar ataxia. Onset is usually in childhood. Pearson syndrome is characterized by sideroblastic anemia and exocrine pancreas dysfunction and is usually fatal in infancy. PEO, characterized by ptosis, paralysis of the extraocular muscles (ophthalmoplegia), oropharyngeal weakness, and variably severe proximal limb weakness, is relatively benign. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1203]
Spinocerebellar ataxia type 15 (SCA15) is characterized by slowly progressive gait and limb ataxia, often in combination with ataxic dysarthria, titubation, upper limb postural tremor, mild hyperreflexia, gaze-evoked nystagmus, and impaired vestibulo-ocular reflex gain. Onset is between ages seven and 72 years, usually with gait ataxia but sometimes with tremor. Affected individuals remain ambulatory for ten to 54 years after symptom onset. Mild dysphagia usually after two or more decades of symptoms has been observed in members of multiple affected families and movement-induced oscillopsia has been described in one member of an affected family. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1362]
Hepatoerythropoietic porphyria (HEP) is characterized by (1) blistering skin lesions, hypertrichosis, and scarring over the affected skin areas; and (2) no increased risk for hepatocellular carcinoma (HCC). Disease manifestations occur during infancy or childhood and with similar frequency in girls and boys. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK169003]
Congenital Cataracts, Facial Dysmorphism, and Neuropathy
Congenital cataracts, facial dysmorphism, and neuropathy (CCFDN) is characterized by abnormalities of the eye (bilateral congenital cataracts, microcornea, microphthalmia, micropupils); mildly dysmorphic facial features apparent in late childhood; and a hypo/demyelinating, symmetric, distal peripheral neuropathy. The neuropathy is predominantly motor at the onset and results in delays in early motor development, progressing to severe disability by the third decade. Secondary scoliosis and foot deformities are common. Sensory neuropathy develops after age ten years. Most affected individuals have a mild non-progressive intellectual deficit and cerebellar involvement including ataxia, nystagmus, intention tremor, and dysmetria. All have short stature and subnormal weight. Adults have hypogonadotropic hypogonadism. Parainfectious rhabdomyolysis (profound muscle weakness, myoglobinuria, and excessively elevated serum concentration of creatine kinase usually following a viral infection) is a potentially life-threatening complication. To date all affected individuals and carriers identified have been from the Roma/Gypsy population. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK25565]
Familial monosomy 7 is typically characterized by early-childhood onset of evidence of bone marrow insufficiency/failure associated with increased risk for myelodysplastic syndrome (MDS) or acute myelogenous leukemia (AML). Bone marrow failure/MDS/AML follows within a few months to years of identification of a monosomy 7 cell line in peripheral blood. Nearly all individuals reported with familial mosaic monosomy 7 have died of their disease. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK45015]
Krabbe disease is characterized by infantile-onset progressive neurologic deterioration and death before age two years (85%-90% of individuals) or by onset between age one year and the fifth decade with slower disease progression (10%-15%). Children with the infantile form appear to be normal for the first few months of life but show extreme irritability, spasticity, and developmental delay before age six months; psychomotor regression progresses to a decerebrate state with no voluntary movement. The onset and progression in the late-onset forms can be quite variable. Individuals can be clinically normal until weakness, vision loss, and intellectual regression become evident. The onset of symptoms and clinical course can be variable even among siblings. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1238]
Alpha-thalassemia (α-thalassemia) has two clinically significant forms: hemoglobin Bart hydrops fetalis (Hb Bart) syndrome and hemoglobin H (HbH) disease. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1435]
Oculocutaneous albinism type 4 (OCA4) is characterized by hypopigmentation of the skin and hair plus the characteristic ocular changes found in all other types of albinism, including nystagmus; reduced iris pigment with iris translucency; reduced retinal pigment with visualization of the choroidal blood vessels on ophthalmoscopic examination; foveal hypoplasia associated with reduction in visual acuity; and misrouting of the optic nerves at the chiasm associated with alternating strabismus, reduced stereoscopic vision, and an altered visual evoked potential (VEP). Individuals with OCA4 are usually recognized within the first year of life because of hypopigmentation of the hair and skin and the ocular features of nystagmus and strabismus. Vision is likely to be stable after early childhood. The amount of cutaneous pigmentation in OCA4 ranges from minimal to near normal. Newborns with OCA4 usually have some pigment in their hair, with color ranging from silvery white to light yellow. Hair color may darken with time, but does not vary significantly from childhood to adulthood. This form of albinism is rarer than OCA2, except in the Japanese population. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1510]
CATSPER-related male infertility results from abnormalities in sperm and can be either CATSPER-related nonsyndromic male infertility (NSMI) or the deafness-infertility syndrome (DIS) when associated with non-progressive prelingual sensorineural hearing loss. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK22925]
ALK-Related Neuroblastic Tumor Susceptibility
ALK-related neuroblastic tumor susceptibility results from heterozygosity for a germline ALK activating pathogenic variant in the tyrosine kinase domain that predisposes to neuroblastic tumors. The spectrum of neuroblastic tumors includes neuroblastoma, ganglioneuroblastoma, and ganglioneuroma. Neuroblastoma is a more malignant tumor and ganglioneuroma a more benign tumor. Depending on the histologic findings ganglioneuroblastoma can behave in a more aggressive fashion, like neuroblastoma, or in a benign fashion, like ganglioneuroma. At present there are no data regarding the lifetime risk to an individual with a germline ALK pathogenic variant of developing a neuroblastic tumor. Preliminary data from the ten reported families with ALK-related neuroblastic tumor susceptibility suggest that the overall penetrance is around 57% with the risk for neuroblastic tumor development highest in infancy and decreasing by late childhood. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK24599]
The 1q21.1 recurrent microdeletion itself does not appear to lead to a clinically recognizable syndrome as some persons with the deletion have no obvious clinical findings and others have variable findings that most commonly include microcephaly (50%), mild intellectual disability (30%), mildly dysmorphic facial features, and eye abnormalities (26%). Other findings can include cardiac defects, genitourinary anomalies, skeletal malformations, and seizures (~15%). Psychiatric and behavioral abnormalities can include autism spectrum disorders, attention deficit hyperactivity disorder, autistic features, and sleep disturbances. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK52787]
Fatty Acid Hydroxylase-Associated Neurodegeneration
Fatty acid hydroxylase-associated neurodegeneration (FAHN) is characterized by central nervous system involvement including corticospinal tract involvement (spasticity), mixed movement disorder (ataxia/dystonia), eye findings (optic atrophy, oculomotor abnormalities) early in the disease course, and progressive intellectual impairment and seizures later in the disease course. FAHN is considered to be a subtype of neurodegeneration with brain iron accumulation (NBIA). To date, a total of 25 individuals from seven families of diverse ethnicity with FAHN have been described; much is yet to be learned about the clinical manifestations and natural history. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK56080]
Adenine Phosphoribosyltransferase Deficiency
Adenine phosphoribosyltransferase (APRT) deficiency is characterized by excessive production of 2,8-dihydroxyadenine (DHA), which is excreted in the urine, where it is poorly soluble and leads to kidney stone formation and chronic kidney disease (CKD). Kidney stones, the most common clinical manifestation of APRT deficiency, can occur at any age; in at least 50% of affected individuals symptoms do not occur until adulthood. In a significant number of individuals, intratubular and interstitial precipitation of DHA crystals can result in kidney failure (i.e., DHA crystal nephropathy). [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK100238]
KAT6B-related disorders include genitopatellar syndrome (GPS) and Say-Barber-Biesecker variant of Ohdo syndrome (Ohdo syndrome, SBBYS variant, or SBBYSS [Say-Barber-Biesecker-Young-Simpson syndrome]). Both phenotypes are characterized by significant global developmental delay/intellectual disability, hypotonia, genital abnormalities in males (cryptorchidism), and patellar hypoplasia/agenesis. Congenital heart defects, dental anomalies, hearing loss, and thyroid anomalies are common to both phenotypes. Also observed in GPS are flexion contractures of the hips and knees, club feet, agenesis of the corpus callosum with microcephaly, and hydronephrosis and/or multiple renal cysts. In SBBYS lower extremity joint stiffness, long thumbs/great toes, immobile mask-like face, blepharophimosis/ptosis, and lacrimal duct anomalies are observed. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK114806]
Marinesco-Sjögren syndrome (MSS) is characterized by cerebellar ataxia with cerebellar atrophy, early-onset (not necessarily congenital) cataracts, mild to severe intellectual disability, hypotonia, and muscle weakness. Additional features are short stature and various skeletal abnormalities including scoliosis. Children with MSS usually present with muscular hypotonia in early infancy; distal and proximal muscular weakness is noticed during the first decade of life. Later, cerebellar findings of truncal ataxia, dysdiadochokinesia, and dysarthria become apparent. Motor function worsens progressively for some years, then stabilizes at an unpredictable age and degree of severity. Cataracts can develop rapidly and typically require lens extraction in the first decade of life. Although many adults are severely handicapped, life span in MSS appears to be near normal. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1192]
Milroy disease is characterized by lower-limb lymphedema, present as pedal edema at (or before) birth or developing soon after. Occasionally it develops later in life. The severity of edema shows both inter- and intrafamilial variability. Swelling is usually bilateral but can be asymmetric. The degree of edema can progress but in some instances can improve, particularly in early years. Other features sometimes associated with Milroy disease include hydrocele (37% of males), prominent veins (23%), upslanting toenails (14%), papillomatosis (10%), and urethral abnormalities in males (4%). Cellulitis, which can damage the lymphatic vessels, occurs in approximately 20% of affected individuals, with infection significantly more likely in males than females. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1239]
Hand-foot-genital syndrome (HFGS) is characterized by limb malformations and urogenital defects. Mild bilateral shortening of the thumbs and great toes, caused primarily by shortening of the distal phalanx and/or the first metacarpal or metatarsal, is the most common limb malformation and results in impaired dexterity or apposition of the thumbs. Urogenital abnormalities include: abnormalities of the ureters and urethra and various degrees of incomplete Müllerian fusion in females; hypospadias of variable severity with or without chordee in males. Vesicoureteral reflux, recurrent urinary tract infections, and chronic pyelonephritis are common; fertility is normal. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1423]
Inherited systemic hyalinosis is characterized by hyaline deposits in the papillary dermis and other tissues. It typically presents at birth or in infancy with severe pain with movement, progressive joint contractures, and often with severe motor disability, thickened skin, and hyperpigmented macules/patches over bony prominences of the joints. Gingival hypertrophy, skin nodules, pearly papules of the face and neck, and perianal masses are common. Complications of protein-losing enteropathy and failure to thrive can be life threatening. Cognitive development is normal. Many children with the severe form (previously called infantile systemic hyalinosis) die in early childhood; some with a milder phenotype (previously called juvenile hyaline fibromatosis) survive into adulthood. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1525]
Spinal Muscular Atrophy, X-Linked Infantile
X-linked infantile spinal muscular atrophy (XL-SMA) is characterized by congenital hypotonia and areflexia and evidence of degeneration and loss of anterior horn cells (i.e., lower motor neurons) in the spinal cord and brain stem. Often congenital contractures and/or fractures are present. Intellect is normal. Life span is shortened because of progressive ventilatory insufficiency resulting from chest muscle involvement. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK2594]
Short-Chain Acyl-CoA Dehydrogenase Deficiency
The clinical findings in those with confirmed short-chain acyl-coA dehydrogenase (SCAD) deficiency range from severe (dysmorphic facial features, feeding difficulties/failure to thrive, metabolic acidosis, ketotic hypoglycemia, lethargy, developmental delay, seizures, hypotonia, dystonia, and myopathy) to normal. As in other fatty acid oxidation disorders, characteristic biochemical findings of SCAD deficiency may be absent except during times of physiologic stress such as fasting and illness. In the largest series of affected individuals published to date, 20% had failure to thrive, feeding difficulties, and hypotonia; 22% had seizures, and 30% had hypotonia without seizures. In contrast, the majority of infants with SCAD deficiency have been detected by expanded newborn screening, and the great majority of these infants remain asymptomatic. Because most infants with SCAD deficiency identified through newborn screening programs have been well at the time of diagnosis and asymptomatic relatives who meet diagnostic criteria are reported, the relationship of clinical manifestations to SCAD deficiency has come into question. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK63582]
X-Linked Congenital Stationary Night Blindness
X-linked congenital stationary night blindness (CSNB) is characterized by: non-progressive retinal findings of reduced visual acuity ranging from 20/30 to 20/200; defective dark adaptation; refractive error, most typically myopia ranging from low (-0.25 diopters [D] to -4.75 D) to high (≥-10.00 D) but occasionally hyperopia; nystagmus; strabismus; normal color vision; and normal fundus examination. Two overlapping, yet distinct, phenotypes are recognized: Complete CSNB (CSNB1A), caused by mutations in NYX (45%) Incomplete CSNB (CSNB2A), caused by mutations in CACNA1F (55%) [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1245]
Coffin-Siris syndrome (CSS) is characterized by aplasia or hypoplasia of the distal phalanx or nail of the fifth digit, distinctive facial features, and moderate to severe developmental/cognitive delay. Expressive language is more severely affected than receptive language. On average, children with CSS learn to sit at 12 months, walk at 30 months, and speak their first words at 24 months. Other findings commonly include failure to thrive, feeding difficulties, short stature, ophthalmologic abnormalities, microcephaly, brain malformations, and hearing loss. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK131811]
Udd Distal Myopathy - Tibial Muscular Dystrophy
Udd distal myopathy is characterized by weakness of ankle dorsiflexion and inability to walk on the heels after age 35 years. Disease progression is slow and muscle weakness remains confined to the anterior tibial muscles. The long toe extensors become clinically involved after ten to 20 years, leading to foot drop and clumsiness when walking. In the mildest form, Udd distal myopathy can remain unnoticed even in the elderly. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1323]
Alkaptonuria is caused by deficiency of homogentisate 1,2-dioxygenase, an enzyme that converts homogentisic acid (HGA) to maleylacetoacetic acid in the tyrosine degradation pathway. The three major features of alkaptonuria are the presence of HGA in the urine, ochronosis (bluish-black pigmentation in connective tissue), and arthritis of the spine and larger joints. Oxidation of the HGA excreted in the urine produces a melanin-like product and causes the urine to turn dark upon standing. Ochronosis occurs only after age 30 years; arthritis often begins in the third decade. Other manifestations include pigment deposition, aortic or mitral valve calcification or regurgitation and occasionally aortic dilatation, renal stones, and prostate stones. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1454]
Fumarate hydratase deficiency results in severe neonatal and early infantile encephalopathy that is characterized by poor feeding, failure to thrive, hypotonia, lethargy, and seizures. Dysmorphic facial features include frontal bossing, depressed nasal bridge, and widely spaced eyes. Many affected individuals are microcephalic. A spectrum of brain abnormalities are seen on magnetic resonance imaging, including cerebral atrophy, enlarged ventricles and generous extra-axial cerebral spinal fluid (CSF) spaces, delayed myelination for age, thinning of the corpus callosum, and an abnormally small brain stem. Brain malformations including bilateral polymicrogyria and absence of the corpus callosum can also be observed. Development is severely affected: most affected individuals are non-verbal and non-ambulatory, and many die during early childhood. Less severely affected individuals with moderate cognitive impairment and long-term survival have been reported. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1506]
Hereditary Myopathy with Early Respiratory Failure
Hereditary myopathy with early respiratory failure (HMERF) is a slowly progressive myopathy that typically begins in the third to fifth decades of life. The usual presenting findings are gait disturbance relating to distal leg weakness or nocturnal respiratory symptoms due to respiratory muscle weakness. Weakness eventually generalizes and affects both proximal and distal muscles. Most affected individuals require walking aids within a few years of onset; some progress to wheelchair dependence and require nocturnal noninvasive ventilatory support. The disease course varies even among individuals within the same family: some remain ambulant until their 70s whereas others may require ventilator support in their 40s. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK185330]
Susceptibility to Infection-Induced Acute Encephalopathy 3
Infection-induced acute encephalopathy 3 (IIAE3) is the susceptibility to recurrent acute necrotizing encephalopathy (ANE) caused by a heterozygous pathogenic variant in RANBP2. ANE refers to the specific neurologic presentation in which bilateral symmetric thalamic, midbrain, and/or hindbrain lesions occur within days following the onset of an acute viral illness caused by influenza A, influenza B, parainfluenza II, human herpesvirus 6, coxsackie virus, or an enterovirus. Although most IIAE3 occurs before age six years, first episodes have been observed in teenagers and adults. ANE begins within 12 hours to three or four days of the first awareness of viral symptoms (fever, cough, rhinorrhea, vomiting, diarrhea, and malaise). The most common sign of ANE is lethargy that progresses to coma (which may last for weeks) and seizures (in 50%). One third of affected individuals die during the acute phase of the encephalopathy; of the survivors, one half have permanent neurologic damage and the remainder have no discernible residual symptoms. Fifty per cent of persons with IIAE3 will have at least one repeat episode and some will have multiple repeat episodes [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK258641]
FBLN5-related cutis laxa is characterized by cutis laxa, early childhood-onset pulmonary emphysema, peripheral pulmonary artery stenosis, and other evidence of a generalized connective disorder such as inguinal hernias and hollow viscus diverticula (e.g., intestine, bladder). Occasionally, supravalvular aortic stenosis is observed. Intrafamilial variability in age of onset is observed. Cardiorespiratory failure from complications of pulmonary emphysema (respiratory or cardiac insufficiency) is the most common cause of death. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK5201]
Cardiofaciocutaneous (CFC) syndrome is characterized by cardiac abnormalities (pulmonic stenosis and other valve dysplasias, septal defects, hypertrophic cardiomyopathy, rhythm disturbances), distinctive craniofacial appearance, and cutaneous abnormalities (including xerosis, hyperkeratosis, ichthyosis, keratosis pilaris, ulerythema ophryogenes, eczema, pigmented moles, hemangiomas, and palmoplantar hyperkeratosis). The hair is typically sparse, curly, fine or thick, woolly or brittle; eyelashes and eyebrows may be absent or sparse. Nails may be dystrophic or fast growing. Some form of neurologic and/or cognitive delay (ranging from mild to severe) is seen in all affected individuals. Neoplasia, mostly acute lymphoblastic leukemia (ALL), has been reported in some individuals. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1186]
Pachyonychia congenita (PC) is characterized by hypertrophic nail dystrophy, painful palmoplantar keratoderma and blistering, oral leukokeratosis, pilosebaceous cysts (including steatocystoma and vellus hair cysts), palmoplantar hyperhydrosis, and follicular keratoses on the trunk and extremities. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1280]
X-linked adrenoleukodystrophy (X-ALD) affects the nervous system white matter and the adrenal cortex. Three main phenotypes are seen in affected males: The childhood cerebral form manifests most commonly between ages four and eight years. It initially resembles attention deficit disorder or hyperactivity; progressive impairment of cognition, behavior, vision, hearing, and motor function follow the initial symptoms and often lead to total disability within two years. Adrenomyeloneuropathy (AMN) manifests most commonly in the late twenties as progressive paraparesis, sphincter disturbances, sexual dysfunction, and often, impaired adrenocortical function; all symptoms are progressive over decades. "Addison disease only" presents with primary adrenocortical insufficiency between age two years and adulthood and most commonly by age 7.5 years, without evidence of neurologic abnormality; however, some degree of neurologic disability (most commonly AMN) usually develops later. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1315]
Choroideremia (CHM) is characterized by progressive chorioretinal degeneration in affected males and milder signs in carrier females. Typically, symptoms in affected males evolve from night blindness to peripheral visual field loss, with central vision preserved until late in life. Although carrier females are generally asymptomatic, signs of chorioretinal degeneration can be observed with careful fundus examination. These signs become more readily apparent after the second decade. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1337]
Acid sphingomyelinase (ASM) deficiency has been categorized in the past as either neuronopathic (Niemann-Pick disease type A [NPD-A]), with death in early childhood, or non-neuronopathic (Niemann-Pick disease type B [NPD-B]). While forms intermediate to these two extremes occur, all ASM deficiency that is not NPD-A is designated in this review as NPD-B, despite its wide range of manifestations and severity. The first symptom in NPD-A is hepatosplenomegaly, usually noted by age three months; over time the liver and spleen become massive. Psychomotor development progresses no further than the 12-month level, after which neurologic deterioration is relentless. A classic cherry-red spot of the macula of the retina, which may not be present in the first few months, is eventually present in all affected children. Interstitial lung disease caused by storage of sphingomyelin in pulmonary macrophages results in frequent respiratory infections and often respiratory failure. Most children succumb before the third year. NPD type B, later in onset and milder in manifestations than NPD type A, is characterized by hepatosplenomegaly with progressive hypersplenism and stable liver dysfunction, gradual deterioration in pulmonary function, osteopenia, and atherogenic lipid profile. Progressive and/or clinically significant neurologic manifestations occur infrequently. Survival to adulthood can occur. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1370]
PLOD1-Related Kyphoscoliotic Ehlers-Danlos Syndrome
Ehlers-Danlos syndrome (EDS), kyphoscoliotic form (previously known as EDS VI) is a generalized connective tissue disorder characterized by friable, hyperextensible skin, thin scars, and easy bruising; generalized joint laxity; severe muscular hypotonia at birth; progressive scoliosis, present at birth or within the first year of life; and scleral fragility with increased risk of rupture of the globe. Intelligence is normal; life span may be normal, but affected individuals are at risk for rupture of medium-sized arteries and respiratory compromise if kyphoscoliosis is severe. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1462]
Mucolipidosis II (ML II, I-cell disease) is a slowly progressive inborn error of metabolism with clinical onset at birth and fatal outcome most often in early childhood. Postnatal growth is limited and often ceases in the second year of life; contractures develop in all large joints. The skin is thickened, facial features are coarse, and gingiva are hypertrophic. Orthopedic abnormalities present at birth may include thoracic deformity, kyphosis, clubfeet, deformed long bones, and/or dislocation of the hip(s). Already in infancy skeletal radiographs reveal dysostosis multiplex. All children appear to have cardiac involvement, most commonly thickening and insufficiency of the mitral valve and, less frequently, the aortic valve. Progressive mucosal thickening narrows the airways and gradual stiffening of the thoracic cage contributes to respiratory insufficiency, the most common cause of death. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1828]
The KANSL1-related intellectual disability syndrome is characterized by developmental delay/intellectual disability, neonatal/childhood hypotonia, dysmorphisms, congenital malformations, and behavioral features. Global psychomotor developmental delay is noted in all individuals from an early age. The majority of individuals with the KANSL1-related intellectual disability syndrome function in the mild to moderate range of intellectual disability. Other findings include epilepsy (55%), congenital heart defects (39%), renal and urologic anomalies (37%), and cryptorchidism (71% of males). Behavior in most is described as friendly, amiable, and cooperative. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK24676]
CARASIL (cerebral autosomal recessive arteriopathy with subcortical infarcts and leukoencephalopathy) is characterized by early-onset changes in the deep white matter of the brain observed on MRI and associated neurologic findings. The most frequent initial symptom is gait disturbance from spasticity beginning between ages 20 and 30 years. Twenty-three percent of affected individuals have stroke-like episodes before age 40 years. Mood changes (apathy and irritability), pseudobulbar palsy, and cognitive dysfunction begin between ages 20 and 50 years. The disease progresses slowly over the five to 20 years following the onset of neurologic symptoms. Scalp alopecia before age 30 years and acute mid- to lower-back pain (lumbago) with onset between ages ten and 40 years are characteristic. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK32533]
Systemic primary carnitine deficiency (CDSP) is a disorder of the carnitine cycle that results in defective fatty acid oxidation. It encompasses a broad clinical spectrum including: Metabolic decompensation in infancy typically presenting between age three months and two years with episodes of hypoketotic hypoglycemia, poor feeding, irritability, lethargy, hepatomegaly, elevated liver transaminases, and hyperammonemia triggered by fasting or common illnesses such as upper respiratory tract infection or gastroenteritis; Childhood myopathy involving heart and skeletal muscle with onset between age two and four years; Fatigability in adulthood; or Absence of symptoms. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK84551]
Mucolipidosis IV is characterized by severe psychomotor delay evident by the end of the first year of life and slowly progressive visual impairment during the first decade as a result of a combination of corneal clouding and retinal degeneration. By the end of the first decade of life and certainly by their early teens, all individuals with typical mucolipidosis IV have severe visual impairment as a result of retinal degeneration. Neurodegeneration is thought to occur in no more than 15% of individuals. About 5% of individuals have atypical mucolipidosis IV, often manifest as less severe psychomotor retardation and/or eye findings. Although in the past, mucolipidosis IV was considered an Ashkenazi Jewish disease, currently most affected individuals are non-Ashkenazi Jewish. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1214]
Branchiootorenal spectrum disorders comprise branchiootorenal (BOR) syndrome and branchiootic syndrome (BOS).BOR is characterized by malformations of the outer, middle, and inner ear associated with conductive, sensorineural, or mixed hearing impairment, branchial fistulae and cysts, and renal malformations ranging from mild renal hypoplasia to bilateral renal agenesis. Some individuals progress to end-stage renal disease (ESRD) later in life. BOS has the same features as BOR syndrome but without renal involvement. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1380]
Charcot-Marie-Tooth hereditary neuropathy type 2A (CMT2A) is a classic axonal peripheral sensorimotor neuropathy characterized by earlier and more severe involvement of the lower extremities than the upper extremities, distal upper-extremity involvement as the neuropathy progresses, more prominent motor deficits than sensory deficits, and normal (>42 m/s) or only slightly decreased nerve conduction velocities (NCVs). Postural tremor is common. Most affected individuals develop symptoms in the first or second decade. It has recently been suggested that CMT2A represents more than 90% of the severe dominant CMT2 cases. However, milder late-onset cases and unusual presentations have also been described. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1511]
PLA2G6-associated neurodegeneration (PLAN) comprises a continuum of three phenotypes with overlapping clinical and radiologic features: Classic infantile neuroaxonal dystrophy (INAD) Atypical neuroaxonal dystrophy (atypical NAD) PLA2G6-related dystonia-parkinsonism [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1675]
KCNQ3-related disorders discussed in this GeneReview are benign familial neonatal epilepsy (BFNE) and benign familial infantile epilepsy (BFIE), seizure disorders that occur in children who have normal psychomotor development. In BFNE seizures begin in an otherwise healthy infant between days two and eight of life and spontaneously disappear between the first and the sixth to 12th month of life. Seizures are generally brief, lasting one to two minutes. Seizure types include tonic or apneic episodes, focal clonic activity, and autonomic changes. Motor activity may be confined to one body part, migrate to other regions, or generalize. Infants are well between seizures and feed normally. In BFIE seizures begin about age six months (range 3-8 months) and disappear about age two years. Seizures are generally brief, lasting two minutes; they appear as daily repeated clusters. Seizure type is usually focal, but can be also generalized, causing diffuse hypertonia with jerks of the limbs, head deviation, or motor arrest with unconsciousness and cyanosis. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK201978]
VCAN-related vitreoretinopathy, which includes Wagner syndrome and erosive vitreoretinopathy (ERVR), is characterized by “optically empty vitreous” on slit-lamp examination and avascular vitreous strands and veils, mild or occasionally moderate to severe myopia, presenile cataract, night blindness of variable degree associated with progressive chorioretinal atrophy, retinal traction and retinal detachment at advanced stages of the disease, and reduced visual acuity. Optic nerve inversion has also been described. Systemic abnormalities are not observed. The first signs usually become apparent during early adolescence, but onset can be as early as age two years. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK3821]
Legius syndrome is characterized by multiple café au lait macules without neurofibromas or other tumor manifestations of neurofibromatosis type 1 (NF1). Additional clinical manifestations reported commonly include intertriginous freckling, lipomas, macrocephaly, and learning disabilities / ADHD / developmental delays. Current knowledge of the natural history of Legius syndrome is based on the clinical manifestations of fewer than 200 individuals with a molecularly confirmed diagnosis; better delineation of the clinical manifestations and natural history of Legius syndrome will likely occur as more affected individuals are identified. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK47312]
Individuals with the 15q13.3 microdeletion are at increased risk for a wide range of clinical manifestations including intellectual disability, seizures, autism spectrum disorders, and schizophrenia; however, the microdeletion itself does not appear to lead to a clinically recognizable syndrome and a subset of persons with the deletion have no obvious clinical findings. Behavioral problems are common and mainly comprise poor attention span, hyperactivity, mood disorder, and aggressive and/or impulsive behavior. Intellectual disability, observed in about half of the individuals with this recurrent deletion, is usually mild but can be moderate to severe. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK50780]
Capillary Malformation-Arteriovenous Malformation Syndrome
RASA1-related disorders are characterized by the presence of multiple, small (1-2 cm in diameter) capillary malformations mostly localized on the face and limbs. About 30% of affected individuals also have associated arteriovenous malformations (AVMs) and/or arteriovenous fistulas (AFVs), fast-flow vascular anomalies that typically arise in the skin, muscle, bone, spine, and brain; life-threatening complications of these lesions can include bleeding, congestive heart failure, and/or neurologic consequences. Symptoms from intracranial AVMs/AVFs seem to occur early in life. Several individuals with a RASA1 mutation have the clinical diagnosis of Parkes Weber syndrome (multiple micro-AVFs associated with a cutaneous capillary stain and excessive soft tissue and skeletal growth of an affected limb). [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK52764]
Pseudoxanthoma elasticum (PXE) is a systemic disorder that affects the elastic tissue of the skin, the eye, and the cardiovascular and gastrointestinal systems. Individuals most commonly present with papules in the skin and/or with angioid streaks of the retina found on routine eye examination or associated with retinal hemorrhage. Rarely, individuals may present with vascular signs and symptoms, such as gastrointestinal bleeding, angina, or intermittent claudication. The most frequent cause of morbidity and disability in PXE is reduced vision from macular hemorrhage and disciform scarring of the macula. Most affected individuals live a normal life span. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1113]
Weill-Marchesani syndrome (WMS) is a connective tissue disorder characterized by abnormalities of the lens of the eye, proportionate short stature, brachydactyly, and joint stiffness. The ocular problems, typically recognized in childhood, include microspherophakia (small spherical lens), myopia secondary to the abnormal shape of the lens, ectopia lentis (abnormal position of the lens), and glaucoma, which can lead to blindness. Height of adult males is 142-169 cm; height of adult females is 130-157 cm. Autosomal recessive and autosomal dominant WMS cannot be distinguished by clinical findings alone. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1114]
Hidrotic ectodermal dysplasia 2, or Clouston syndrome (referred to as HED2 throughout this GeneReview) is characterized by partial or total alopecia, dystrophy of the nails, hyperpigmentation of the skin (especially over the joints), and clubbing of the fingers. Sparse scalp hair and dysplastic nails are seen early in life. In infancy, scalp hair is wiry, brittle, patchy, and pale; progressive hair loss may lead to total alopecia by puberty. The nails may be milky white in early childhood; they gradually become dystrophic, thick, and distally separated from the nail bed. Palmoplantar keratoderma may develop during childhood and increases in severity with age. The clinical manifestations are highly variable even within the same family. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1200]
Berardinelli-Seip Congenital Lipodystrophy
Berardinelli-Seip congenital lipodystrophy (BSCL) is usually diagnosed at birth or soon thereafter. Because of the absence of functional adipocytes, lipid is stored in other tissues, including muscle and liver. Affected individuals develop insulin resistance and approximately 25%-35% develop diabetes mellitus between ages 15 and 20 years. Hepatomegaly secondary to hepatic steatosis and skeletal muscle hypertrophy occur in all affected individuals. Hypertrophic cardiomyopathy is reported in 20%-25% of affected individuals and is a significant cause of morbidity from cardiac failure and early mortality. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1212]
Simpson-Golabi-Behmel syndrome type 1 (SGBS1) is characterized by pre- and postnatal macrosomia; distinctive craniofacies (including macrocephaly, coarse facial features, macrostomia, macroglossia, palatal abnormalities); and commonly, mild to severe intellectual disability with or without structural brain anomalies. Other variable findings include supernumerary nipples, diastasis recti/umbilical hernia, congenital heart defects, diaphragmatic hernia, genitourinary defects, and GI anomalies. Skeletal anomalies can include vertebral fusion, scoliosis, rib anomalies, and congenital hip dislocation. Hand anomalies can include large hands and postaxial polydactyly. Affected individuals are at increased risk for embryonal tumors, including Wilms tumor, hepatoblastoma, adrenal neuroblastoma, gonadoblastoma, and hepatocellular carcinoma. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1219]
ROR2-related Robinow syndrome is characterized by distinctive craniofacial features, skeletal abnormalities, and other anomalies. Craniofacial features include macrocephaly, broad prominent forehead, low-set ears, ocular hypertelorism, prominent eyes, midface hypoplasia, short upturned nose with depressed nasal bridge and flared nostrils, large and triangular mouth with exposed incisors and upper gums, gum hypertrophy, misaligned teeth, ankyloglossia, and micrognathia. Skeletal abnormalities include short stature with growth retardation, mesomelic or acromesomelic limb shortening, hemivertebrae with fusion of thoracic vertebrae, and brachydactyly. Other common features include micropenis with or without cryptorchidism in males and reduced clitoral size and hypoplasia of the labia majora in females, renal tract abnormalities, and nail hypoplasia or dystrophy. The disorder is recognizable at birth or in early childhood. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1240]
Refsum disease is characterized by anosmia and early-onset retinitis pigmentosa, which are both universal findings with variable combinations of neuropathy, deafness, ataxia, and ichthyosis. Onset of symptoms ranges from age seven months to over age 50 years. Cardiac arrhythmia and heart failure caused by cardiomyopathy are potentially severe health problems which develop later in life. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1353]
Lysinuric protein intolerance (LPI) typically presents after an infant is weaned; variable findings include recurrent vomiting and episodes of diarrhea, episodes of stupor and coma after a protein-rich meal, poor feeding, aversion to protein-rich food, failure to thrive, hepatosplenomegaly, and muscular hypotonia. Over time, findings include: poor growth; osteoporosis; involvement of the lungs (progressive interstitial changes; pulmonary alveolar proteinosis) and of kidneys (progressive glomerular and proximal tubular disease); hematologic abnormalities (normochromic or hypochromic anemia, leukopenia, thrombocytopenia, erythroblastophagocytosis at the bone marrow aspirate) and a clinical presentation resembling the hemophagocytic lymphohistiocytosis/macrophagic activation syndrome. Acute pancreatitis can also be seen. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1361]
Hereditary Hearing Loss and Deafness Overview
Hereditary hearing loss and deafness may be conductive, sensorineural, or a combination of both; syndromic (associated with malformations of the external ear or other organs or with medical problems involving other organ systems) or nonsyndromic (no associated visible abnormalities of the external ear or any related medical problems); and prelingual (before language develops) or postlingual (after language develops). [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1434]
GDAP1-Related Hereditary Motor and Sensory Neuropathy
Charcot-Marie-Tooth neuropathy type 4A (CMT4A), an aggressive form of hereditary motor and sensory neuropathy (HMSN), is confined to the peripheral nervous system, and typically affects the lower extremities earlier and more severely than the upper extremities. As the neuropathy progresses, the distal upper extremities also become severely affected. Even proximal muscles can become weak. Age at onset is from infancy to early childhood. In most cases, disease progression causes disabilities within the first or second decade of life. At the end of the second decade, most individuals are wheelchair bound. Disease progression varies considerably even within the same family. The neuropathy can be either of the demyelinating type with reduced nerve conduction velocities or the axonal type with normal nerve conduction velocities. Vocal cord paresis is common. Intelligence is normal. Life expectancy is usually not affected, but on occasion may be reduced because of secondary complications. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1539]
Mucolipidosis III gamma (ML III gamma) is a slowly progressive disorder characterized by childhood onset of radiographic evidence of mild to moderate dysostosis multiplex; joint stiffness and pain initially in the shoulders, hips, and fingers; and gradual mild coarsening of facial features. Cardiorespiratory complications (restrictive lung disease, thickening and insufficiency of the mitral and aortic valves, left ventricular hypertrophy) can be significant. A few affected individuals have mild cognitive impairment. Because ML III gamma has only recently been distinguished from the more common ML III alpha/beta, previously published descriptions of ML III may have inadvertently included both of these disorders. Thus, much is to yet be learned about the specific manifestations and natural history of ML III gamma. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK24701]
Glycogen storage disease type III (GSD III) is characterized by variable liver, cardiac muscle, and skeletal muscle involvement. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK26372]
The findings in X-linked chondrodysplasia punctata 2 (CDPX2) range from fetal demise with multiple malformations and severe growth retardation to much milder manifestations, including adults with no recognizable physical abnormalities. At least 95% of liveborn individuals with CDPX2 are female with the following findings:Growth deficiency/short stature Distinctive craniofacial appearance Skeletal changes: stippling (chondrodysplasia punctate) on x-rays of the epiphyses of the long bones and vertebrae, the trachea and distal ends of the ribs seen in children prior to completion of normal epiphyseal ossification; rhizomelic (i.e., proximal) shortening of limbs that is often asymmetric; scoliosis Ectodermal changes: linear or blotchy scaling ichthyosis in the newborn that usually resolves in the first months of life leaving linear or whorled atrophic patches involving hair follicles (follicular atrophoderma); coarse hair with scarring alopecia; occasional flattened or split nails; normal teeth Ocular changes: cataracts; microphthalmia and/or microcornea [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK55062]
The two forms of deoxyguanosine kinase (DGUOK) deficiency are a hepatocerebral mitochondrial DNA depletion syndrome (multisystem disease in neonates) and isolated hepatic disease later in infancy or childhood. The majority of affected individuals have the multisystem illness with hepatic disease (cholestasis) and neurologic dysfunction evident within weeks of birth. They subsequently manifest severe hypotonia, developmental regression, and typical rotary nystagmus that evolves into opsoclonus. Those with isolated liver disease may also have renal involvement and some later develop mild hypotonia. Progressive hepatic disease is the most common cause of death in both forms. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK7040]
The urea cycle disorders (UCD) result from defects in the metabolism of waste nitrogen from the breakdown of protein and other nitrogen-containing molecules. Severe deficiency or total absence of activity of any of the first four enzymes (CPS1, OTC, ASS, ASL) in the urea cycle or the cofactor producer (NAGS) results in the accumulation of ammonia and other precursor metabolites during the first few days of life. Infants with a severe urea cycle disorder are normal at birth but rapidly develop cerebral edema and the related signs of lethargy, anorexia, hyper- or hypoventilation, hypothermia, seizures, neurologic posturing, and coma. In milder (or partial) deficiencies of these enzymes and in arginase (ARG) deficiency, ammonia accumulation may be triggered by illness or stress at almost any time of life. In these disorders the elevations of plasma ammonia concentration and symptoms are often subtle and the first recognized clinical episode may not occur for months or decades. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1217]
The MECP2 duplication syndrome is a severe neurodevelopmental disorder characterized by infantile hypotonia, delayed psychomotor development leading to severe intellectual disability, poor speech development, progressive spasticity, recurrent respiratory infections (in ~75% of affected individuals) and seizures (in ~50%). MECP2 duplication syndrome is 100% penetrant in males. Occasionally females have been described with a MECP2 duplication and related clinical findings, often associated with concomitant X-chromosomal abnormalities that prevent inactivation of the duplicated region. Generalized tonic-clonic seizures are most often observed; atonic seizures and absence seizures have also been described. One third of affected males are never able to walk independently. Almost 50% of affected males die before age 25 years, presumably from complications of recurrent infection and/or neurologic deterioration. In addition to the core features, autistic behaviors and gastrointestinal dysfunction have been observed in several affected boys. Although interfamilial phenotypic variability is observed, severity is usually consistent within families. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1284]
Hereditary neuralgic amyotrophy (HNA) is characterized by sudden onset of severe, non-abating pain in the shoulder girdle and/or the upper limb and amyotrophy (muscle wasting or atrophy) that typically develops within two weeks of the onset of severe pain. Other sites may also be involved in an attack; sensory symptoms, present in the majority of affected individuals, can include hypoesthesia (decreased sensation) and paresthesias. Onset is typically in the second or third decade (median age 28 years). Although attacks appear to become less frequent with age, residual deficits accumulate with subsequent attacks. In some families, non-neurologic findings (characteristic craniofacial features, bifid uvula or cleft palate, short stature, and/or partial syndactyly of the fingers or toes) are present. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1395]
CASK-related disorders include a spectrum of phenotypes in both females and males. The two main types of clinical presentation are: Microcephaly with pontine and cerebellar hypoplasia (MICPCH), generally associated with loss-of-function CASK mutations; and X-linked intellectual disability (XLID) with or without nystagmus, generally associated with hypomorphic CASK mutations. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK169825]
MCT8-specific thyroid hormone cell-membrane transporter deficiency is characterized by severe cognitive deficiency, infantile hypotonia, diminished muscle mass and generalized muscle weakness, progressive spastic quadriplegia, joint contractures, and dystonic and/or athetoid movement with characteristic paroxysms or kinesigenic dyskinesias. Seizures occur in about 25% of cases. Most affected males never sit or walk independently or lose these abilities over time; most never speak or have severely dysarthric speech. Brain MRI obtained in the first few years of life shows transient delayed myelination, which improves by age four years. Although psychomotor findings observed in affected males do not occur in heterozygous females, the latter often have thyroid test abnormalities intermediate between affected and normal individuals. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK26373]
CHCHD10-related disorders are characterized by a spectrum of adult-onset neurologic findings that can include:Mitochondrial myopathy (may also be early-onset): weakness, amyotrophy, exercise intolerance Amyotrophic lateral sclerosis (ALS): progressive degeneration of upper motor neurons (UMNs) and lower motor neurons (LMNs) Frontotemporal dementia (FTD): slowly progressive behavioral changes, language disturbances, cognitive decline, extrapyramidal signs Late-onset spinal motor neuronopathy (SMAJ): weakness, cramps and/or fasciculations; areflexia; neurogenic bladder Cerebellar ataxia: gait ataxia, kinetic ataxia (progressive loss of coordination of lower- and upper-limb movements), dysarthria/dysphagia, nystagmus, cerebellar oculomotor disorder [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK304142]
DFNA2 nonsyndromic hearing loss is characterized by symmetric, predominantly high-frequency sensorineural hearing loss (SNHL) that is progressive across all frequencies. At younger ages, hearing loss tends to be mild in the low frequencies and moderate in the high frequencies; in older persons, the hearing loss is moderate in the low frequencies and severe to profound in the high frequencies. Although the hearing impairment is often detected during routine hearing assessment of a school-age child, it is likely that hearing is impaired from birth, especially at high frequencies. Most affected persons initially require hearing aids to assist with sound amplification between ages ten and 40 years. By age 70 years, all persons with DFNA2 nonsyndromic hearing loss have severe-to-profound hearing impairment. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1209]
X-linked juvenile retinoschisis is characterized by symmetric bilateral macular involvement with onset in the first decade of life, in some cases as early as age three months. Fundus examination shows areas of schisis (splitting of the nerve fiber layer of the retina) in the macula, sometimes giving the impression of a spoke wheel pattern. Schisis of the peripheral retina, predominantly inferotemporally, occurs in approximately 50% of individuals. Affected males typically have vision of 20/60 to 20/120. Visual acuity often deteriorates during the first and second decades of life but then remains relatively stable until the fifth or sixth decade. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1222]
PNPLA6-related disorders span a phenotypic continuum characterized by variable combinations of cerebellar ataxia, upper motor neuron involvement manifesting as spasticity and/or brisk reflexes, chorioretinal dystrophy associated with variable degrees of reduced visual function, and hypogonadotropic hypogonadism (delayed puberty and lack of secondary sex characteristics), either in isolation or as part of anterior hypopituitarism (growth hormone, thyroid hormone, or gonadotropin deficiencies). Common but less frequent features are peripheral neuropathy (usually of axonal type manifesting as reduced distal reflexes, diminished vibratory sensation, and/or distal muscle wasting), hair anomalies (long eyelashes, bushy eyebrows, or scalp alopecia), short stature, and impaired cognitive functioning (learning disabilities in children and deficits in attention, visuospatial abilities, and recall in adults). Some of these features can occur in distinct clusters on the phenotypic continuum: Boucher-Neuhäuser syndrome (cerebellar ataxia, chorioretinal dystrophy, and hypogonadotropic hypogonadism); Gordon Holmes syndrome (cerebellar ataxia, hypogonadotropic hypogonadism, and – to a variable degree – brisk reflexes); Oliver-McFarlane syndrome (trichomegaly, chorioretinal dystrophy, short stature, intellectual disability, and hypopituitarism); Laurence-Moon syndrome; and spastic paraplegia type 39 (SPG39) (upper motor neuron involvement, peripheral neuropathy, and sometimes reduced cognitive functioning and/or cerebellar ataxia). [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK247161]
Primary hyperoxaluria type 2 (PH2), caused by deficiency of the enzyme glyoxylate reductase/hydroxypyruvate reductase (GR/HPR), is characterized by recurrent nephrolithiasis (deposition of calcium oxalate in the renal pelvis/urinary tract), nephrocalcinosis (deposition of calcium oxalate in the renal parenchyma), and end-stage renal disease (ESRD). After ESRD, oxalosis (widespread tissue deposition of calcium oxalate) usually develops. Symptom onset is typically in childhood. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK2692]
Unverricht-Lundborg disease (EPM1) is a neurodegenerative disorder characterized by onset from age six to 15 years, stimulus-sensitive myoclonus, and tonic-clonic epileptic seizures. Some years after the onset, ataxia, incoordination, intentional tremor, and dysarthria develop. Individuals with EPM1 are mentally alert but show emotional lability, depression, and mild decline in intellectual performance over time. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1142]
The clinical manifestations of glycogen storage disease type IV (GSD IV) discussed in this entry span a continuum of different subtypes with variable ages of onset, severity, and clinical features. Clinical findings vary extensively both within and between families.The fatal perinatal neuromuscular subtype presents in utero with fetal akinesia deformation sequence (FADS) with decreased fetal movements, polyhydramnios, and fetal hydrops. Death usually occurs in the neonatal period. The congenital neuromuscular subtype presents in the newborn period with profound hypotonia, respiratory distress, and dilated cardiomyopathy. Death usually occurs in early infancy. Infants with the classic (progressive) hepatic subtype may appear normal at birth, but rapidly develop failure to thrive; hepatomegaly, liver dysfunction, and progressive liver cirrhosis; hypotonia; and cardiomyopathy. Without liver transplantation, death from liver failure usually occurs by age five years. Children with the non-progressive hepatic subtype tend to present with hepatomegaly, liver dysfunction, myopathy, and hypotonia; however, they are likely to survive without progression of the liver disease and may not show cardiac, skeletal muscle, or neurologic involvement. The childhood neuromuscular subtype is rare and the course is variable, ranging from onset in the second decade with a mild disease course to a more severe, progressive course resulting in death in the third decade. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK115333]
Hereditary Leiomyomatosis and Renal Cell Cancer
Hereditary leiomyomatosis and renal cell cancer (HLRCC) is characterized by cutaneous leiomyomata (multiple or single in 76% of affected individuals), uterine leiomyomata (fibroids), and/or a single renal tumor. Cutaneous leiomyomata appear as skin-colored to light brown papules or nodules distributed over the trunk and extremities, and occasionally on the face, and appear at a mean age of 25 years, increasing in size and number with age. Uterine leiomyomata are present in almost all females with HLRCC and tend to be numerous and large; age at diagnosis ranges from 18 to 52 years, with most women experiencing irregular or heavy menstruation and pelvic pain. Renal tumors causing hematuria, lower back pain, and a palpable mass are usually unilateral, solitary, and aggressive and range from type 2 papillary to tubulo-papillary to collecting-duct carcinomas. They occur in about 10%-16% of individuals with HLRCC; the median age of detection is 44 years. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1252]
ARSACS (autosomal recessive spastic ataxia of Charlevoix-Saguenay) is characterized in individuals born in Quebec Province by early-onset (age 12-18 months) difficulty in walking and gait unsteadiness. In individuals with ARSACS born outside the Province of Quebec, onset is often delayed until later childhood and even adulthood. Ataxia, dysarthria, spasticity, extensor plantar reflexes, distal muscle wasting, a distal sensorimotor neuropathy predominant in the legs, and horizontal gaze-evoked nystagmus constitute the most frequent progressive neurologic signs. Increased demarcation of the retinal nerve fibers located near the vessels close to the optic disc (formerly designated as yellow streaks of hypermyelinated fibers) is very common in individuals with ARSACS who originate from Quebec but may be absent in non-Quebec born individuals. Individuals with ARSACS born in the Province of Quebec become wheelchair bound at the average age of 41 years; cognitive skills are preserved in the long term as individuals remain able to perform daily living tasks late into adulthood. Death commonly occurs in the sixth decade. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1255]
Lymphedema-distichiasis syndrome is characterized by lower-limb lymphedema and distichiasis (aberrant eyelashes ranging from a full set of extra eyelashes to a single hair). Lymphedema typically appears in late childhood or puberty, is confined to the lower limbs, and is often asymmetric; severity varies within families. Males develop edema at an earlier age and have more problems with cellulitis than females. Distichiasis, which may be present at birth, is observed in 94% of affected individuals. About 75% of affected individuals have ocular findings including corneal irritation, recurrent conjunctivitis, and photophobia; other common findings include varicose veins, congenital heart disease, and ptosis. About 25% of individuals are asymptomatic. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1457]
Dopamine beta-hydroxylase (DBH) deficiency is characterized by lack of sympathetic noradrenergic function but normal parasympathetic and sympathetic cholinergic function. Affected individuals exhibit profound deficits in autonomic regulation of cardiovascular function that predispose to orthostatic hypotension. Although DBH deficiency appears to be present from birth, the diagnosis is not generally recognized until late childhood. The combination of ptosis of the eyelids in infants and children, together with hypotension, is suggestive of the disease. In the perinatal period, DBH deficiency has been complicated by vomiting, dehydration, hypotension, hypothermia, and hypoglycemia requiring repeated hospitalization; children have reduced exercise capacity. By early adulthood, individuals have profound orthostatic hypotension, greatly reduced exercise tolerance, ptosis of the eyelids, and nasal stuffiness. Presyncopal symptoms include dizziness, blurred vision, dyspnea, nuchal discomfort, and chest pain. Life expectancy is unknown, but some affected individuals have lived beyond 60 years. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1474]
Clinical features of achondrogenesis type 1B (ACG1B) include extremely short limbs with short fingers and toes, hypoplasia of the thorax, protuberant abdomen, and hydropic fetal appearance caused by the abundance of soft tissue relative to the short skeleton. The face is flat, the neck is short, and the soft tissue of the neck may be thickened. Death occurs prenatally or shortly after birth. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1516]
FRMD7-related infantile nystagmus (FIN) is characterized by either the onset of horizontal, conjugate, gaze-dependent nystagmus in the first six months of life or periodic alternating nystagmus (with cyclical changes of nystagmus direction) of infantile onset. Binocular vision and color vision are normal and visual acuity is typically better than 6/12. An abnormal head posture is seen in approximately 15% of affected individuals. The eyes are structurally normal and electrophysiologic studies, such as visual evoked potential (VEP) and electroretinogram (ERG), are normal. Affected females report slightly better visual acuity than affected males; however, no differences between males and females in the amplitude, frequency, and waveform of nystagmus are observed. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK3822]
Microphthalmia with Linear Skin Defects Syndrome
Microphthalmia with linear skin defects (MLS) syndrome is characterized by unilateral or bilateral microophthalmia and/or anophthalmia and linear skin defects, usually involving the face and neck, which are present at birth and heal with age, leaving minimal residual scarring. Other findings can include central nervous system involvement (e.g., structural anomalies, infantile seizures), developmental delay, heart defects (e.g., hypertrophic cardiomyopathy, oncocytic cardiomyopathy, arrhythmias), short stature, diaphragmatic hernia, nail dystrophy, preauricular pits and hearing loss, and genitourinary malformations. Inter- and intrafamilial variability is considerable. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK7041]
16p11.2 microdeletion is characterized by developmental delay, intellectual disability, and/or autism spectrum disorder (ASD). Developmental delays are more related to diminished language and cognitive function than motor disability. Although IQ scores range from mild intellectual disability to normal, those with IQ scores in the average range typically have other developmental issues such as language delay or ASD. Expressive language appears to be more affected than receptive language. Individuals with 16p11.2 microdeletion are at increased risk of being overweight and obese, and may be at higher than average risk for seizures and/or EEG abnormalities. As a group, they do not have a higher risk for other severe neurologic disorders, or other medical problems. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK11167]
Nijmegen breakage syndrome (NBS) is characterized by progressive microcephaly, intrauterine growth retardation and short stature, recurrent sinopulmonary infections, an increased risk for cancer, and premature ovarian failure in females. Developmental milestones are attained at the usual time during the first year; however, borderline delays in development and hyperactivity may be observed in early childhood. Intellectual abilities tend to decline over time and most children tested after age seven years have mild to moderate intellectual disability. Recurrent pneumonia and bronchitis may result in respiratory failure and early death. Approximately 40% of affected individuals have developed malignancies before age 20 years, with the risk being highest for T-cell (55%) and B-cell lymphomas (45%). Other tumors include T-cell lymphoma and solid tumors (e.g., medulloblastoma, glioma, and rhabdomyosarcoma). Note, however, that much of what is reported about NBS is based on individuals who are homozygous for the single most common Eastern European pathogenic variant, 657_661del5. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1176]
Hereditary hyperekplexia (HPX) is characterized by generalized stiffness immediately after birth that normalizes during the first years of life; excessive startle reflex (eye blinking and a flexor spasm of the trunk) to unexpected (particularly auditory) stimuli; and a short period of generalized stiffness following the startle response during which voluntary movements are impossible. Exaggerated head-retraction reflex (HRR) consisting of extension of the head followed by violent flexor spasms of limbs and neck muscles elicited by tapping the tip of the nose is observed in most children. Other findings include periodic limb movements in sleep (PLMS) and hypnagogic (occurring when falling asleep) myoclonus. Sudden infant death (SIDS) has been reported. Intellect is usually normal; mild intellectual disability may occur. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1260]
Vascular Ehlers-Danlos Syndrome (vEDS) is characterized by thin, translucent skin; easy bruising; characteristic facial appearance (in some individuals); and arterial, intestinal, and/or uterine fragility. Vascular dissection or rupture, gastrointestinal perforation, or organ rupture are the presenting signs in the majority of adults identified to have vEDS. Arterial rupture may be preceded by aneurysm, arteriovenous fistulae, or dissection but also may occur spontaneously. Neonates may present with clubfoot and/or congenital dislocation of the hips. In childhood, inguinal hernia, pneumothorax, recurrent joint subluxation or dislocation, and bruising can occur. Pregnancy for women with vEDS has an estimated 5.3% risk for death from peripartum arterial rupture or uterine rupture. One fourth of individuals with vEDS, confirmed by laboratory testing, experienced a major complication by age 20 years and more than 80% by age 40 years. The median age of death in this reviewed population was 50 years. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1494]
Hypertrophic cardiomyopathy (HCM) is typically defined by the presence of unexplained left ventricular hypertrophy (LVH). Such LVH occurs in a non-dilated ventricle in the absence of other cardiac or systemic disease capable of producing the observed magnitude of increased LV wall thickness, such as pressure overload (e.g., long-standing hypertension, aortic stenosis) or storage/infiltrative disorders (e.g., Fabry disease, amyloidosis). The clinical manifestations of HCM range from asymptomatic LVH to progressive heart failure to sudden cardiac death (SCD), and vary from individual to individual even within the same family. Common symptoms include shortness of breath (particularly with exertion), chest pain, palpitations, orthostasis, presyncope, and syncope. Most often the LVH of HCM becomes apparent during adolescence or young adulthood, although it may also develop late in life, in infancy, or in childhood. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1768]
ZAP70-related severe combined immunodeficiency (ZAP70-related SCID) is a cell-mediated immunodeficiency caused by abnormal T-cell receptor (TCR) signaling. Affected children usually present in the first year of life with recurrent bacterial, viral, and opportunistic infections, diarrhea, and failure to thrive. Severe lower-respiratory infections and oral candidiasis are common. Affected children usually do not survive past their second year without hematopoietic stem cell transplantation (HSCT). [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK20221]
Spastic paraplegia 3A (SPG3A) is a hereditary spastic paraplegia (HSP) characterized by progressive bilateral and mostly symmetric spasticity and weakness of the legs, diminished vibration sense caused by degeneration of the corticospinal tracts and dorsal columns, and urinary bladder hyperactivity. The average age of onset is four years. More than 80% of reported individuals manifest spastic gait before the end of the first decade of life. Most persons with early-onset SPG3A have a “pure” (“uncomplicated”) HSP; however, complicated HSP with axonal motor neuropathy and/or distal amyotrophy with lower motor neuron involvement (Silver syndrome phenotype) have been observed. The rate of progression in SPG3A is slow, and wheelchair dependency or need for a walking aid (cane, walker, or wheelchair) is relatively rare. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK45978]
The branchiooculofacial syndrome (BOFS) is characterized by: branchial (cervical [90%] or infra- or supra-auricular [60%]) skin defects that range from barely perceptible thin skin or hair patch to erythematous “hemangiomatous” lesions to large weeping erosions; ocular anomalies that can include microphthalmia, anophthalmia, coloboma, and nasolacrimal duct stenosis/atresia; and facial anomalies that can include ocular hypertelorism or telecanthus, broad nasal tip, upslanted palpebral fissures, cleft lip or prominent philtral pillars that give the appearance of a repaired cleft lip (formerly called "pseudocleft lip") with or without cleft palate, upper lip pits and lower facial weakness (asymmetric crying face or partial 7th cranial nerve weakness). Malformed and prominent pinnae and hearing loss from inner ear and/or petrous bone anomalies are common. Intellect is usually normal. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK55063]
Erythropoietic Protoporphyria, Autosomal Recessive
Erythropoietic protoporphyria (EPP) is characterized by cutaneous photosensitivity (usually beginning in infancy or childhood) that results in tingling, burning, pain, and itching within minutes of sun/light exposure and may be accompanied by swelling and redness. Blistering lesions are uncommon. Symptoms (which may seem out of proportion to the visible skin lesions) may persist for hours or days after the initial phototoxic reaction. Photosensitivity usually remains for life. Multiple episodes of acute photosensitivity may lead to chronic changes of sun-exposed skin (lichenification, leathery pseudovesicles, grooving around the lips) and loss of lunulae of the nails. Approximately 20%-30% of individuals with EPP have some degree of liver dysfunction, which is typically mild with slight elevations of the liver enzymes. Up to 5% may develop more advanced liver disease which may be accompanied by motor neuropathy similar to that seen in the acute porphyrias. Except for the small minority with advanced liver disease, life expectancy is not reduced. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK100826]
Spastic paraplegia 7 (SPG7) is characterized by insidiously progressive bilateral lower limb weakness and spasticity. Most affected individuals have proximal or generalized weakness in the legs and impaired vibration sense. Onset is mostly in adulthood, although symptoms may start as early as age 11 years and as late as age 72 years. Additional features such as hyperreflexia in the arms, sphincter disturbances, spastic dysarthria, dysphagia, pale optic disks, ataxia, nystagmus, strabismus, decreased hearing, scoliosis, pes cavus, motor and sensory neuropathy, and amyotrophy may be observed. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1107]
Geleophysic dysplasia, a progressive condition resembling a lysosomal storage disorder, is characterized by short stature, short hands and feet, progressive joint limitation and contractures, distinctive facial features, progressive cardiac valvular disease, and thickened skin. Intellect is normal. Major findings are likely to be present in the first year of life. Cardiac, respiratory, and lung involvement result in death before age five years in approximately 33% of individuals with geleophysic dysplasia 1. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK11168]
Cherubism is characterized by progressive, painless, bilateral enlargement of the mandible and/or maxilla resulting from replacement of bone with multilocular cysts composed of fibrotic stromal cells and osteoclast-like cells. The enlargement is usually symmetric in nature. The phenotype ranges from no clinical manifestations to severe mandibular and maxillary overgrowth with respiratory, vision, speech, and swallowing problems. Onset is typically between ages two and five years. Other bones are usually not affected and the affected person is otherwise normal. The jaw lesions progress slowly until puberty when they stabilize and then regress. Dental abnormalities include congenitally missing teeth, premature exfoliation of the deciduous teeth, and displacement of permanent teeth by the jaw lesions. By age 30 years, facial abnormalities are no longer apparent; residual jaw deformity is rare. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1137]
Oral-facial-digital syndrome type I (OFD1) is associated with dysfunction of primary cilia and is characterized by the following abnormalities: Oral (lobed tongue, hamartomas or lipomas of the tongue, cleft of the hard or soft palate, accessory gingival frenulae, hypodontia, and other dental abnormalities) Facial (widely spaced eyes or telecanthus, hypoplasia of the alae nasi, median cleft or pseudocleft upper lip, micrognathia) Digital (brachydactyly, syndactyly of varying degrees, and clinodactyly of the fifth finger; duplicated hallux [great toe]; preaxial or postaxial polydactyly of the hands) Brain (intracerebral cysts, corpus callosum agenesis, cerebellar agenesis with or without Dandy-Walker malformation) Kidney (polycystic kidney disease) [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1188]
ALS2-related disorders involve retrograde degeneration of the upper motor neurons of the pyramidal tracts and comprise a clinical continuum from infantile ascending hereditary spastic paraplegia (IAHSP) to juvenile forms without lower motor neuron involvement (juvenile primary lateral sclerosis [JPLS]) to forms with lower motor neuron involvement (autosomal recessive juvenile amyotrophic lateral sclerosis [JALS]). IAHSP is characterized by onset of spasticity with increased reflexes and sustained clonus of the lower limbs within the first two years of life, progressive weakness and spasticity of the upper limbs by age seven to eight years, and wheelchair dependence in the second decade with progression toward severe spastic tetraparesis and a pseudobulbar syndrome. JPLS is characterized by onset and loss of ability to walk during the second year of life, progressive signs of upper motor neuron disease, wheelchair dependence by adolescence, and later loss of motor speech production. JALS is characterized by onset during childhood (mean age of onset 6.5 years), spasticity of facial muscles, uncontrolled laughter, spastic dysarthria, spastic gait, inconstant moderate muscle atrophy, bladder dysfunction, and sensory disturbances; some individuals are bedridden by age 12 to 50 years. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1243]
SOX2-related eye disorders are characterized by anophthalmia and/or microphthalmia that is usually bilateral, severe, and apparent at birth or by prenatal ultrasound examination. Other common findings include brain malformations, esophageal atresia, cryptorchidism and/or micropenis in males, and hypogonadotropic hypogonadism and/or pituitary hypoplasia. Postnatal growth failure, delayed motor development, and learning disability are common. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1300]
Clinical features of atelosteogenesis type 2 (AO2) include rhizomelic limb shortening with normal-sized skull, hitchhiker thumbs, small chest, protuberant abdomen, cleft palate, and distinctive facial features (midfaceretrusion, depressed nasal bridge, epicanthus, micrognathia). Other typical findings are ulnar deviation of the fingers, gap between the first and second toes, and clubfoot. AO2 is lethal at birth or shortly thereafter because of pulmonary hypoplasia and tracheobronchomalacia. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1317]
X-linked Opitz G/BBB syndrome (XLOS) is a multiple congenital anomaly disorder characterized by facial anomalies (ocular hypertelorism, prominent forehead, widow's peak, broad nasal bridge, anteverted nares), laryngotracheoesophageal defects, and genitourinary abnormalities (hypospadias, cryptorchidism, and hypoplastic/bifid scrotum). Developmental delay and intellectual disability are observed in about 50% of affected males. Cleft lip and/or palate are present in approximately 50% of affected individuals. Other malformations present in fewer than 50% of individuals include congenital heart defects, imperforate or ectopic anus, and midline brain defects (Dandy-Walker malformation and agenesis or hypoplasia of the corpus callosum and/or cerebellar vermis). Wide clinical variability occurs even among members of the same family. Female carriers usually manifest only ocular hypertelorism. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1327]
Manitoba oculotrichoanal (MOTA) syndrome is characterized by an aberrant hairline (unilateral or bilateral wedge-shaped extension of the anterior hairline from the temple region to the ipsilateral eye) and anomalies of the eyes (ocular hypertelorism, anophthalmia/microphthalmia, cryptophthalmos, colobomas of the upper eyelid and corneopalpebral synechiae), nose (bifid or wide with a notched tip), abdominal wall (omphalocele or umbilical hernia), and anus (stenosis and/or anterior displacement of the anal opening). The manifestations and degree of severity vary even among affected members of the same family. Growth and psychomotor development are normal. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1728]
Mandibulofacial Dysostosis with Microcephaly
Mandibulofacial dysostosis with microcephaly (MFDM) is characterized by malar and mandibular hypoplasia; microcephaly (congenital or postnatal onset); malformations of the pinna, auditory canal, and/or middle ear (ossicles and semi-circular canals) with associated conductive hearing loss; and distinctive facial features (metopic ridge, up- or downslanting palpebral fissures, prominent glabella, broad nasal bridge, bulbous nasal tip, and everted lower lip). Associated craniofacial malformations may include cleft palate, choanal atresia, and facial asymmetry. Intellectual disability is a prominent feature. Major extracranial malformations include: esophageal atresia (~40%), congenital heart disease (~40%), and thumb abnormalities (~25%). Short stature is present in approximately one third of individuals. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK214367]
The disorder of congenital mirror movements (CMM) is characterized by early-onset, obvious mirror movements (involuntary movements of one side of the body that mirror intentional movements on the opposite side) in individuals with no other clinical signs or symptoms. Although mirror movements vary in severity, most affected individuals have strong and sustained mirror movements of a lesser amplitude than the corresponding voluntary movements. Mirror movements usually persist throughout life, without deterioration or improvement, and are not associated with subsequent onset of additional neurologic manifestations. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK279760]
Hyperornithinemia-Hyperammonemia-Homocitrullinuria Syndrome
Hyperornithinemia-hyperammonemia-homocitrullinuria (HHH) syndrome is characterized by variable clinical presentation and age of onset.Chronic neurocognitive deficits (including developmental delay, ataxia, spasticity, learning disabilities, cognitive deficits and/or unexplained seizures); Acute encephalopathy secondary to hyperammonemic crisis precipitated by a variety of factors; and Chronic liver dysfunction (unexplained elevation of liver transaminases with or without mild coagulopathy, with or without mild hyperammonemia and protein intolerance). [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK97260]
Giant axonal neuropathy (GAN) is an early-onset fatal neurodegenerative disorder. GAN starts as severe peripheral motor and sensory neuropathy during infancy and evolves into central nervous system impairment (intellectual disability, seizures, cerebellar signs, and pyramidal tract signs). Most individuals become wheelchair dependent in the second decade of life and eventually bedridden with severe polyneuropathy, ataxia, and dementia. Death usually occurs in the third decade. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1136]
Hereditary coproporphyria (HCP) is an acute (hepatic) porphyria in which the acute symptoms are neurovisceral and occur in discrete episodes. Attacks typically start in the abdomen with low-grade pain that slowly increases over a period of days (not hours) with nausea progressing to vomiting. In some individuals, the pain is predominantly in the back or extremities. When an acute attack is untreated, a motor neuropathy may develop over a period of days or a few weeks. The neuropathy first appears as weakness proximally in the arms and legs, then progresses distally to involve the hands and feet. Some individuals experience respiratory insufficiency due to loss of innervation of the diaphragm and muscles of respiration. Acute attacks are associated commonly with use of certain medications, caloric deprivation, and changes in female reproductive hormones. About 20% of those with an acute attack also experience photosensitivity associated with bullae and skin fragility. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK114807]
Lesch-Nyhan syndrome is characterized by motor dysfunction that resembles cerebral palsy, cognitive and behavioral disturbances, and uric acid overproduction (hyperuricemia). The most common presenting features, hypotonia and developmental delay, are evident by age three to six months. Affected children are delayed in sitting and most never walk. Within the first few years, extrapyramidal involvement (e.g., dystonia, choreoathetosis, opisthotonos) and pyramidal involvement (e.g., spasticity, hyperreflexia, extensor plantar reflexes) become evident. Cognitive impairment and behavioral disturbances emerge between ages two and three years. Persistent self-injurious behavior (biting the fingers, hands, lips, and cheeks; banging the head or limbs) is a hallmark of the disease. Overproduction of uric acid may lead to deposition of uric acid crystals or calculi in the kidneys, ureters, or bladder. Gouty arthritis may occur later in the disease. Related disorders with less severe manifestations include hyperuricemia with neurologic dysfunction but no self-injurious behavior and hyperuricemia alone, sometimes with acute renal failure. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1149]
Camurati-Engelmann disease (CED) is characterized by hyperostosis of the long bones and the skull, proximal muscle weakness, severe limb pain, a wide-based, waddling gait, and joint contractures. Facial features such as frontal bossing, enlargement of the mandible, proptosis, and cranial nerve impingement resulting in facial palsy are seen in severely affected individuals later in life. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1156]
Neonatal/infantile (severe) Canavan disease is characterized by macrocephaly, lack of head control, and developmental delays usually noted by age three to five months. As children get older hypotonia becomes severe and failure to achieve independent sitting, ambulation, or speech become apparent. Hypotonia eventually changes to spasticity. Assistance with feeding becomes necessary. Life expectancy is usually into the teens. Mild/juvenile Canavan disease is characterized by mild developmental delay that can go unrecognized. Head circumference may be normal. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1234]
OTOF-related deafness (DFNB9 nonsyndromic hearing loss) is characterized by two phenotypes: prelingual nonsyndromic hearing loss and, less frequently, temperature-sensitive nonsyndromic auditory neuropathy (TS-NSAN). The nonsyndromic hearing loss is bilateral severe-to-profound congenital deafness. In the first one or two years of life, OTOF-related deafness can appear to be an auditory neuropathy based on electrophysiologic testing in which auditory brain stem responses (ABRs) are absent and otoacoustic emissions (OAEs) are present. However, with time OAEs disappear and electrophysiologic testing is more consistent with a cochlear defect. The distinction between auditory neuropathy and a cochlear defect is important as cochlear implants may be of marginal value in persons with auditory neuropathy but have been shown to be effective for individuals with OTOF-related deafness. TS-NSAN is characterized by normal-to-mild hearing loss in the absence of fever and significant hearing loss ranging from severe to profound in the presence of fever. When the fever resolves, hearing returns to normal. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1251]
Aicardi syndrome was classically characterized by a triad of features: agenesis of the corpus callosum, distinctive chorioretinal lacunae, and infantile spasms. However, it is now well recognized that several other important findings are typically present in girls with Aicardi syndrome. Neurologic examination can reveal microcephaly, axial hypotonia, and appendicular hypertonia with spasticity. Moderate to severe global developmental delay and intellectual disability are expected. Many girls with Aicardi syndrome develop seizures prior to age three months, and most before age one year. Ongoing medically refractory epilepsy with a variety of seizure types develops over time. Costovertebral defects are common and can lead to marked scoliosis in up to one third of affected individuals. Other features include characteristic facial features, gastrointestinal difficulties, small hands, vascular malformations and pigmentary lesions of the skin, increased incidence of tumors, lower growth rate after ages seven to nine years, and precocious or delayed puberty. Survival is highly variable, with the mean age of death about 8.3 years and the median age of death about 18.5 years. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1381]
X-linked hyper IgM syndrome (HIGM1), a disorder of abnormal T- and B-cell function, is characterized by low serum concentrations of IgG and IgA and normal or elevated serum concentrations of IgM. Mitogen proliferation may be normal, but NK- and T-cell cytotoxicity are frequently impaired. Antigen-specific responses may be decreased or absent. The range of clinical findings varies, even within the same family. Over 50% of males with HIGM1 develop symptoms by age one year, and more than 90% are symptomatic by age four years. HIGM1 usually presents in infancy with recurrent upper- and lower-respiratory tract bacterial infections, opportunistic infections, and recurrent or protracted diarrhea associated with failure to thrive. Neutropenia, thrombocytopenia, and anemia are common. Autoimmune and/or inflammatory disorders, such as sclerosing cholangitis, have been reported. Significant neurologic complications, often the result of a CNS infection, are seen in 10%-15% of affected males. Liver disease, including primary cirrhosis and carcinomas (bile duct carcinomas, hepatocellular carcinomas, adenocarcinomas of the liver and gall bladder), and tumors of the gastrointestinal tract (carcinoid of the pancreas, glucagonoma of the pancreas) are common life-threatening complications in adolescents and young adults with HIGM1. Affected males are also at an increased risk for lymphoma, particularly Hodgkin's disease associated with Epstein-Barr virus infection. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1402]
Alpha-Thalassemia X-Linked Intellectual Disability Syndrome
Alpha-thalassemia X-linked intellectual disability (ATRX) syndrome is characterized by distinctive craniofacial features, genital anomalies, severe developmental delays, hypotonia, intellectual disability, and mild-to-moderate anemia secondary to alpha-thalassemia. Craniofacial abnormalities include small head circumference, telecanthus or widely spaced eyes, short nose, tented vermilion of the upper lip, and thick or everted vermilion of the lower lip with coarsening of the facial features over time. Although all affected individuals have a normal 46,XY karyotype, genital anomalies range from hypospadias and undescended testicles to severe hypospadias and ambiguous genitalia, to normal-appearing female external genitalia. Global developmental delays are evident in infancy and some affected individuals never walk independently or develop significant speech. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1449]
Renal coloboma (papillorenal syndrome) is an autosomal dominant condition characterized by renal hypodysplasia and abnormalities of the optic nerve. Abnormal renal structure or function is noted in 92% of affected individuals; ophthalmologic abnormalities are noted in 77% of affected individuals who have pathogenic variants in PAX2. Renal abnormalities can be clinically silent in rare individuals. In most individuals, clinically significant renal insufficiency/renal failure is reported. End-stage renal disease requiring renal transplant is not uncommon. Ophthalmologic abnormalities are typically described as optic nerve coloboma or dysplasia. Iris colobomas have not been reported in any individual with a PAX2 pathogenic variant. Ophthalmologic abnormalities may significantly impair vision in some individuals, while others have subtle changes only noted after detailed ophthalmologic examination. Additional clinical findings include hearing loss, which is noted in 7% of individuals with identified pathogenic variants in PAX2. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1451]
Urofacial syndrome (UFS) is characterized by prenatal or infantile onset of urinary bladder voiding dysfunction, abnormal facial movement with expression (resulting from abnormal co-contraction of the corners of the mouth and eyes), and often bowel dysfunction (constipation and/or encopresis). Bladder voiding dysfunction increases the risk for urinary incontinence, megacystis, vesicoureteric reflux, hydroureteronephrosis, urosepsis, and progressive renal impairment. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK154138]
GLB1-related disorders comprise two phenotypically distinct lysosomal storage disorders: GM1 gangliosidosis and mucopolysaccharidosis type IVB (MPS IVB). [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK164500]
Autosomal dominant hyper IgE syndrome (AD-HIES) is a primary immune deficiency characterized by the classic triad of recurrent skin boils, cyst-forming pneumonias, and extreme elevations of serum IgE. It is now recognized that other common manifestations include eczema, mucocutaneous candidiasis, and several connective tissue and skeletal abnormalities. A rash in the newborn period subsequently evolves into an eczematoid dermatitis. Recurrent staphylococcal skin boils and bacterial pneumonias usually manifest in the first years of life. Pneumatocoeles and bronchiectasis often result from aberrant healing of pneumonias. Mucocutaneous candidiasis is common. A characteristic facial appearance typically emerges in adolescence. Skeletal abnormalities include osteopenia, minimal trauma fractures, and scoliosis. Vascular abnormalities include middle-sized artery tortuosity and aneurysms, with infrequent clinical sequelae of myocardial infarction and subarachnoid hemorrhage. Gastrointestinal (GI) manifestations include gastroesophageal reflux disease; esophageal dysmotility; and rarely colonic perforations, some of which are associated with diverticuli. Fungal infection of the GI tract (typically histoplasmosis, Cryptococcus, and Coccidioides) also occur infrequently. Survival is typically into adulthood, but life span is often shortened. Most deaths are associated with Gram-negative (Pseudomonas) or filamentous fungal pneumonias resulting in hemoptysis. Lymphomas occur at an increased frequency. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK25507]
Primary hyperoxaluria type 3 (PH3) is characterized by recurring calcium oxalate stones beginning in childhood or adolescence and, on occasion, nephrocalcinosis or reduced kidney function. In 50%-65% of individuals with PH3 stone formation begins prior to age five years. Although the frequency and severity of stone activity often seem to abate by adolescence and adulthood, stone formation can occur throughout life and some adults have many stones. To date systemic oxalosis has not been reported in PH3. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK316514]
Kabuki syndrome (KS) is characterized by typical facial features (elongated palpebral fissures with eversion of the lateral third of the lower eyelid; arched and broad eyebrows; short columella with depressed nasal tip; large, prominent, or cupped ears), minor skeletal anomalies, persistence of fetal fingertip pads, mild to moderate intellectual disability, and postnatal growth deficiency. Other findings may include: congenital heart defects, genitourinary anomalies, cleft lip and/or palate, gastrointestinal anomalies including anal atresia, ptosis and strabismus, and widely spaced teeth and hypodontia. Functional differences can include: increased susceptibility to infections and autoimmune disorders, seizures, endocrinologic abnormalities including isolated premature thelarche in females, feeding problems, and hearing loss. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK62111]
Very Long-Chain Acyl-Coenzyme A Dehydrogenase Deficiency
Deficiency of very long-chain acyl-CoA dehydrogenase (VLCAD), which catalyzes the initial step of mitochondrial β-oxidation of long-chain fatty acids with a chain length of 14 to 20 carbons, is associated with three phenotypes. The severe early-onset cardiac and multi-organ failure form typically presents in the first months of life with hypertrophic or dilated cardiomyopathy, pericardial effusion, and arrhythmias, as well as hypotonia, hepatomegaly, and intermittent hypoglycemia. The hepatic or hypoketotic hypoglycemic form typically presents during early childhood with hypoketotic hypoglycemia and hepatomegaly, but without cardiomyopathy. The later-onset episodic myopathic form presents with intermittent rhabdomyolysis, muscle cramps and/or pain, and/or exercise intolerance. Hypoglycemia typically is not present at the time of symptoms. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK6816]
Multiple Epiphyseal Dysplasia, Recessive
Recessive multiple epiphyseal dysplasia (EDM4/rMED) is characterized by joint pain (usually in the hips or knees); malformations of hands, feet, and knees; and scoliosis. Approximately 50% of affected individuals have an abnormal finding at birth, e.g., clubfoot, clinodactyly, or (rarely) cystic ear swelling. Onset of articular pain is variable but usually occurs in late childhood. Stature is usually within the normal range prior to puberty; in adulthood, stature is only slightly diminished and ranges from 150 to 180 cm. Functional disability is mild. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1306]
Nonsyndromic isolated dilated cardiomyopathy (DCM) is characterized by left ventricular enlargement and systolic dysfunction, a reduction in the myocardial force of contraction. DCM usually presents with any one of the following:Heart failure with symptoms of congestion (edema, orthopnea, paroxysmal nocturnal dyspnea) and/or reduced cardiac output (fatigue, dyspnea on exertion) Arrhythmias and/or conduction system disease Thromboembolic disease (from left ventricular mural thrombus) including stroke [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1309]
X-linked ocular albinism (XLOA) is a disorder of melanosome biogenesis leading to minor cutaneous and adnexal manifestations and congenital and persistent visual impairment in affected males. XLOA is characterized by infantile nystagmus, reduced visual acuity, hypopigmentation of the iris pigment epithelium and the ocular fundus, and foveal hypoplasia. Significant refractive errors, reduced or absent binocular functions, photoaversion, and strabismus are common. XLOA is a non-progressive disorder and the visual acuity remains stable throughout life, often slowly improving into the mid-teens. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1343]
Spinocerebellar ataxia type 17 (SCA17) is characterized by ataxia, dementia, and involuntary movements, including chorea and dystonia. Psychiatric symptoms, pyramidal signs, and rigidity are common. The age of onset ranges from three to 55 years. Individuals with full-penetrance alleles develop neurologic and/or psychiatric symptoms by age 50 years. Ataxia and psychiatric abnormalities are frequently the initial findings, followed by involuntary movement, parkinsonism, dementia, and pyramidal signs. Brain MRI shows variable atrophy of the cerebrum, brain stem, and cerebellum. The clinical features correlate with the length of the polyglutamine expansion but are not absolutely predictive of the clinical course. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1438]
Craniometaphyseal Dysplasia, Autosomal Dominant
Autosomal dominant craniometaphyseal dysplasia (designated AD-CMD in this review) is characterized by progressive diffuse hyperostosis of cranial bones evident clinically as wide nasal bridge, paranasal bossing, widely spaced eyes with an increase in bizygomatic width, and prominent mandible. Development of dentition may be delayed and teeth may fail to erupt as a result of hyperostosis and sclerosis of alveolar bone. Progressive thickening of craniofacial bones continues throughout life, often resulting in narrowing of the cranial foramina, including the foramen magnum. If untreated, compression of cranial nerves can lead to disabling conditions such as facial palsy, blindness, or deafness (conductive and/or sensorineural hearing loss). In individuals with typical uncomplicated AD-CMD life expectancy is normal; in those with severe AD-CMD life expectancy can be reduced as a result of compression of the foramen magnum. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1461]
The allelic disorders of free sialic acid metabolism — Salla disease, intermediate severe Salla disease, and infantile free sialic acid storage disease (ISSD) — are neurodegenerative disorders resulting from increased lysosomal storage of free sialic acid. The mildest phenotype is Salla disease, which is characterized by normal appearance and neurologic findings at birth followed by slowly progressive neurologic deterioration resulting in mild to moderate psychomotor retardation, spasticity, athetosis, and epileptic seizures. The most severe phenotype is ISSD, characterized by severe developmental delay, coarse facial features, hepatosplenomegaly, and cardiomegaly; death usually occurs in early childhood. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1470]
Individuals with X-linked dystonia-parkinsonism (XDP) have dystonia of varying severity and parkinsonism. XDP afflicts primarily Filipino men and, rarely, women. The mean age of onset in men is 39 years; the clinical course is highly variable with parkinsonism as the initial presenting sign, overshadowed by dystonia as the disease progresses. Features of parkinsonism include resting tremor, bradykinesia, rigidity, postural instability, and severe shuffling gait. The dystonia develops focally, most commonly in the jaw, neck, trunk, and eyes, and less commonly in the limbs, tongue, pharynx, and larynx, the most characteristic being jaw dystonia often progressing to neck dystonia. Individuals with pure parkinsonism have non-disabling symptoms that are only slowly progressive; those who develop a combination of parkinsonism and dystonia can develop multifocal or generalized symptoms within a few years and die prematurely from pneumonia or intercurrent infections. Female carriers are mostly asymptomatic, though a small minority may manifest dystonia, parkinsonism, or chorea. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1489]
The phenotypic spectrum of MED12-related disorders, which is still being defined, includes at a minimum the phenotypes of FG syndrome type 1 (FGS1) and Lujan syndrome (LS). FGS1 and LS share the clinical findings of cognitive impairment, hypotonia, and abnormalities of the corpus callosum. FGS1 is further characterized by absolute or relative macrocephaly, tall forehead, downslanted palpebral fissures, small and simple ears, constipation and/or anal anomalies, broad thumbs and halluces, and characteristic behavior. LS is further characterized by large head, tall thin body habitus, long thin face, high nasal root, high narrow palate, and short philtrum. Carrier females in families with FGS1 and LS are typically unaffected. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1676]
Campomelic dysplasia (CD) is a skeletal dysplasia characterized by distinctive facies, Pierre Robin sequence with cleft palate, shortening and bowing of long bones, and club feet. Other findings include laryngotracheomalacia with respiratory compromise and ambiguous genitalia or normal female external genitalia in most individuals with a 46,XY karyotype. Many affected infants die in the neonatal period; additional problems identified in long-term survivors include short stature, cervical spine instability with cord compression, progressive scoliosis, and hearing impairment. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1760]
ATP6V0A2-related cutis laxa, also known as autosomal recessive cutis laxa type 2A (ARCL2A), spans a phenotypic spectrum that includes Debré-type cutis laxa at the severe end and wrinkly skin syndrome at the mild end. Affected individuals have furrowing of the skin of the whole body that improves with time. They may have other evidence of a generalized connective disorder, including enlarged anterior fontanelle in infancy, congenital dislocation of the hips, inguinal hernias, and high myopia. In most (not all) affected individuals, cortical and cerebellar malformations are present and are associated with severe developmental delays, seizures, and neurologic regression. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK5200]
Primary trimethylaminuria is characterized by a fishy odor resembling that of rotten or decaying fish that results from excess excretion of trimethylamine in the urine, breath, sweat, and reproductive fluids. No physical symptoms are associated with trimethylaminuria. Affected individuals appear normal and healthy; however, the unpleasant odor often results in social and psychological problems. Symptoms are usually present from birth and may worsen during puberty. In females, symptoms are more severe just before and during menstruation, after taking oral contraceptives, and around the time of menopause. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1103]
Roberts syndrome (RBS) is characterized by prenatal growth retardation (ranging from mild to severe), craniofacial findings (including microcephaly and cleft lip and/or palate) and limb malformations (including bilateral symmetric tetraphocomelia or hypomelia caused by mesomelic shortening). Upper limbs are more severely affected than lower limbs. Other limb malformations include oligodactyly with thumb aplasia or hypoplasia, syndactyly, clinodactyly, and elbow and knee flexion contractures. Craniofacial abnormalities include cleft lip and/or cleft palate, premaxillary prominence, micrognathia, microbrachycephaly, malar flattening, downslanted palpebral fissures, widely spaced eyes, exophthalmos resulting from shallow orbits, corneal clouding, underdeveloped ala nasi, beaked nose, and ear malformations. Intellectual disability is reported in the majority of affected individuals. Mortality is high among severely affected pregnancies and newborns. Mildly affected individuals may survive to adulthood. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1153]
Frontotemporal Dementia, Chromosome 3-Linked
Chromosome 3-linked frontotemporal dementia (FTD3) has been described in a single family from Denmark and in one individual with familial FTD3 from Belgium. It typically starts between ages 46 and 65 years with subtle personality changes and slowly progressive behavioral changes, dyscalculia, and language disturbances. Disinhibition or loss of initiative is the most common presenting symptom. The disease progresses over a few years into profound dementia with mutism. Several individuals have developed an asymmetric akinetic rigid syndrome with arm and gait dystonia and pyramidal signs that may be related to treatment with neuroleptic drugs. Disease duration may be as short as three years or longer than 20 years. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1199]
Carney complex (CNC) is characterized by skin pigmentary abnormalities, myxomas, endocrine tumors or overactivity, and schwannomas. Pale brown to black lentigines are the most common presenting feature of CNC and typically increase in number at puberty. Cardiac myxomas occur at a young age, may occur in any or all cardiac chambers, and manifest as intracardiac obstruction of blood flow, embolic phenomena, and/or heart failure. Other sites for myxomas include the skin, breast, oropharynx, and female genital tract. Primary pigmented nodular adrenocortical disease (PPNAD), which causes Cushing syndrome, is the most frequently observed endocrine tumor in CNC, occurring in approximately 25% of affected individuals. Large-cell calcifying Sertoli cell tumors (LCCSCTs) are observed in one third of affected males within the first decade and in almost all adult males. Up to 75% of individuals with CNC have multiple thyroid nodules, most of which are thyroid follicular adenomas. Clinically evident acromegaly from a growth hormone (GH)-producing adenoma is evident in approximately 10% of adults. Psammomatous melanotic schwannoma (PMS), a rare tumor of the nerve sheath, occurs in an estimated 10% of affected individuals. The median age of diagnosis is 20 years. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1286]
Townes-Brocks syndrome (TBS) is characterized by the triad of:Imperforate anus (82%); Dysplastic ears (88%) (overfolded superior helices and preauricular tags) frequently associated with sensorineural and/or conductive hearing impairment (65%); and Thumb malformations (89%) (triphalangeal thumbs, duplication of the thumb [preaxial polydactyly], and rarely hypoplasia of the thumbs). [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1445]
Retinoblastoma (Rb) is a malignant tumor of the developing retina that occurs in children, usually before age five years. Rb develops from cells that have cancer-predisposing variants in both copies of RB1. Rb may be unifocal or multifocal. About 60% of affected individuals have unilateral Rb with a mean age of diagnosis of 24 months; about 40% have bilateral Rb with a mean age of diagnosis of 15 months. Heritable retinoblastoma is an autosomal dominant susceptibility for Rb. Individuals with heritable retinoblastoma are also at increased risk of developing non-ocular tumors. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1452]
X-linked agammaglobulinemia (XLA) is characterized by recurrent bacterial infections in affected males in the first two years of life. Recurrent otitis is the most common infection prior to diagnosis. Conjunctivitis, sinopulmonary infections, diarrhea, and skin infections are also frequently seen. Approximately 60% of individuals with XLA are recognized as having immunodeficiency when they develop a severe, life-threatening infection such as pneumonia, empyema, meningitis, sepsis, cellulitis, or septic arthritis. S pneumoniae and H influenzae are the most common organisms found prior to diagnosis and may continue to cause sinusitis and otitis after diagnosis and the initiation of gammaglobulin therapy. The prognosis for individuals with XLA has improved markedly in the last 25 years as a result of earlier diagnosis, the development of preparations of gammaglobulin that allow normal concentrations of serum IgG to be achieved, and more liberal use of antibiotics. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1453]
Citrullinemia type I (CTLN1) presents as a clinical spectrum that includes an acute neonatal form (the "classic" form), a milder late-onset form, a form without symptoms or hyperammonemia, and a form in which women have onset of severe symptoms during pregnancy or post partum. Distinction between the clinical forms is based on clinical findings and is not clear-cut. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1458]
ELANE-related neutropenia includes congenital neutropenia and cyclic neutropenia, both of which are primary hematologic disorders characterized by recurrent fever, skin and oropharyngeal inflammation (i.e., mouth ulcers, gingivitis, sinusitis, and pharyngitis), and cervical adenopathy. Infectious complications are generally more severe in congenital neutropenia than in cyclic neutropenia. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1533]
Infantile-onset spinocerebellar ataxia (IOSCA) is a severe, progressive neurodegenerative disorder characterized by normal development until age one year, followed by onset of ataxia, muscle hypotonia, loss of deep-tendon reflexes, and athetosis. Ophthalmoplegia and sensorineural deafness develop by age seven years. By adolescence affected individuals are profoundly deaf and no longer ambulatory; sensory axonal neuropathy, optic atrophy, autonomic nervous system dysfunction, and hypergonadotrophic hypogonadism in females become evident. Epilepsy can develop into a serious and often fatal encephalopathy: myoclonic jerks or focal clonic seizures that progress to epilepsia partialis continua followed by status epilepticus with loss of consciousness. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK3795]
Hypophosphatasia is characterized by defective mineralization of bone and/or teeth in the presence of low activity of serum and bone alkaline phosphatase. Clinical features range from stillbirth without mineralized bone at the severe end to pathologic fractures of the lower extremities in later adulthood at the mild end. At least six clinical forms are currently recognized based on age at diagnosis and severity of features: Perinatal (lethal) hypophosphatasia characterized by respiratory insufficiency and hypercalcemia Perinatal (benign) hypophosphatasia with prenatal skeletal manifestations that slowly resolve into the milder childhood or adult form Infantile hypophosphatasia with onset between birth and age six months of rickets without elevated serum alkaline phosphatase activity Childhood hypophosphatasia that ranges from low bone mineral density for age with unexplained fractures to rickets Adult hypophosphatasia characterized by early loss of adult dentition and stress fractures and pseudofractures of the lower extremities in middle age Odontohypophosphatasia characterized by premature exfoliation of primary teeth and/or severe dental caries as an isolated finding or as part of the above forms of hypophosphatasia [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1150]
Noonan Syndrome with Multiple Lentigines
Noonan syndrome with multiple lentigines (NSML) is a condition in which the cardinal features consist of lentigines, hypertrophic cardiomyopathy, short stature, pectus deformity, and dysmorphic facial features, including widely spaced eyes and ptosis. Multiple lentigines present as dispersed flat, black-brown macules, mostly on the face, neck and upper part of the trunk with sparing of the mucosa. In general, lentigines do not appear until age four to five years but then increase to the thousands by puberty. Some individuals with NSML do not exhibit lentigines. Approximately 85% of affected individuals have heart defects, including hypertrophic cardiomyopathy (HCM) (typically appearing during infancy and sometimes progressive) and pulmonary valve stenosis. Postnatal growth retardation resulting in short stature occurs in fewer than 50% of affected persons, although most affected individuals have a height that is less than the 25th percentile for age. Sensorineural hearing deficits, present in approximately 20%, are poorly characterized. Intellectual disability, typically mild, is observed in approximately 30% of persons with NSML. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1383]
Megalencephalic Leukoencephalopathy with Subcortical Cysts
The classic phenotype of megalencephalic leukoencephalopathy with subcortical cysts (MLC) is characterized by early-onset macrocephaly, often in combination with mild gross motor developmental delay and seizures; gradual onset of ataxia, spasticity, and sometimes extrapyramidal findings; and usually late onset of mild mental deterioration. Macrocephaly, observed in all individuals, may be present at birth but more frequently develops during the first year of life. The degree of macrocephaly is variable and can be as great as 4 to 6 SD above the mean in some individuals. After the first year of life, head growth rate normalizes and growth follows a line parallel to the 98th percentile, usually several centimeters above it. Almost all individuals have epilepsy from an early age. Initial mental and motor development is normal in most cases. Walking is often unstable, followed by ataxia of the trunk and extremities, then minor signs of pyramidal dysfunction and brisk deep-tendon stretch reflexes. Mental deterioration is late and mild. Severity ranges from independent walking for a few years only to independent walking in the fifth decade. Some individuals have died in their teens or twenties; others are alive in their forties. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1535]
G6PC3 deficiency is characterized by severe congenital neutropenia which occurs in a phenotypic continuum that includes the following:Isolated severe congenital neutropenia (nonsyndromic) Classic G6PC3 deficiency (severe congenital neutropenia plus cardiovascular and/or urogenital abnormalities) Severe G6PC3 deficiency (classic G6PC3 deficiency plus involvement of non-myeloid hematopoietic cell lines, additional extra-hematologic features, and pulmonary hypertension; known as Dursun syndrome) [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK285321]
The TP63-related disorders comprise six overlapping phenotypes:Ankyloblepharon-ectodermal defects-cleft lip/palate (AEC) syndrome (which includes Rapp-Hodgkin syndrome) Acro-dermo-ungual-lacrimal-tooth (ADULT) syndrome Ectrodactyly, ectodermal dysplasia, cleft lip/palate syndrome 3 (EEC3) Limb-mammary syndrome Split-hand/foot malformation type 4 (SHFM4) Isolated cleft lip/cleft palate (orofacial cleft 8) [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK43797]
Bietti crystalline dystrophy (BCD) is a chorioretinal degeneration characterized by the presence of yellow-white crystals and/or complex lipid deposits in the retina. Progressive atrophy and degeneration of the retinal pigment epithelium (RPE)/choroid lead to symptoms similar to those of other forms of retinal degeneration that fall under the category of retinitis pigmentosa and allied disorders, namely: reduced visual acuity, poor night vision, abnormal retinal electrophysiology, visual field loss, and often impaired color vision. Marked asymmetry between eyes is common. Onset is typically during the second to third decade of life, but ranges from the early teenage years to beyond the third decade. With time, loss of peripheral visual field, central acuity, or both result in legal blindness in most, if not all, affected individuals. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK91457]
Dent disease, an X-linked disorder of proximal renal tubular dysfunction, is characterized by low molecular-weight (LMW) proteinuria, hypercalciuria, nephrocalcinosis, nephrolithiasis, and chronic kidney disease (CKD). Males younger than age ten years may manifest only low molecular-weight (LMW) proteinuria and/or hypercalciuria, which are usually asymptomatic. Thirty to 80% of affected males develop end-stage renal disease (ESRD) between ages 30 and 50 years; in some instances ESRD does not develop until the sixth decade of life or later. Rickets or osteomalacia are occasionally observed, and mild short stature, although underappreciated, may be a common occurrence. Disease severity can vary within the same family. Males with Dent disease 2 (caused by mutation of OCRL) are at increased risk for intellectual disability. Due to random X-chromosome inactivation, some female carriers may manifest hypercalciuria and, rarely, renal calculi and moderate LMW proteinuria. Females rarely if ever develop CKD. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK99494]
Hutchinson-Gilford progeria syndrome encompasses a spectrum of clinical features that typically develop in childhood and resemble some features of accelerated aging. Although signs and symptoms vary in age of onset and severity, they are remarkably consistent overall. Children with Hutchinson-Gilford progeria syndrome (HGPS) usually appear normal at birth. Profound failure to thrive occurs during the first year. Characteristic facies, with receding mandible, narrow nasal bridge and pointed nasal tip develop. During the first to third year the following usually become apparent: partial alopecia progressing to total alopecia, loss of subcutaneous fat, progressive joint contractures, bone changes, nail dystrophy, and abnormal tightness and/or small soft outpouchings of the skin over the abdomen and upper thighs, and delayed primary tooth eruption. Later findings include low-frequency conductive hearing loss, dental crowding, and partial lack of secondary tooth eruption. Additional findings present in some but not all affected individuals include photophobia, excessive ocular tearing, exposure keratitis, and Raynaud phenomenon. Motor and mental development is normal. Death occurs as a result of complications of severe atherosclerosis, either cardiac disease (myocardial infarction) or cerebrovascular disease (stroke), generally between ages six and 20 years. Average life span is approximately 14.6 years. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1121]
Enlarged parietal foramina are characteristic symmetric, paired radiolucencies of the parietal bones, located close to the intersection of the sagittal and lambdoid sutures, caused by deficient ossification around the parietal notch, which is normally obliterated by the fifth month of fetal development. Enlarged parietal foramina are usually asymptomatic. Meningeal, cortical, and vascular malformations of the posterior fossa occasionally accompany the bone defects and may predispose to epilepsy. In a minority of individuals, headaches, vomiting, or intense local pain are sometimes associated with the defects, especially on application of mild pressure to the unprotected cerebral cortex. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1128]
Familial dysautonomia (FD) affects the development and survival of sensory, sympathetic, and parasympathetic neurons. It is a debilitating disease present from birth. Neuronal degeneration progresses throughout life. Affected individuals have gastrointestinal dysfunction, vomiting crises, recurrent pneumonia, altered sensitivity to pain and temperature perception, and cardiovascular instability. About 40% of individuals have autonomic crises. Hypotonia contributes to delay in acquisition of motor milestones. Older individuals often have a broad-based and ataxic gait that deteriorates over time. Life expectancy is decreased. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1180]
Ehlers-Danlos syndrome (EDS), classic type is a connective tissue disorder characterized by skin hyperextensibility, abnormal wound healing, and joint hypermobility. It includes two previously designated subtypes (EDS type I and EDS type II) that are now recognized to form a continuum of clinical findings. The skin is smooth, velvety to the touch, and hyperelastic; i.e., it extends easily and snaps back after release (unlike lax, redundant skin, as in cutis laxa). The skin is fragile, as manifested by splitting of the dermis following relatively minor trauma, especially over pressure points (knees, elbows) and areas prone to trauma (shins, forehead, chin). Wound healing is delayed, and stretching of scars after apparently successful primary wound healing is characteristic. Complications of joint hypermobility, such as dislocations of the shoulder, patella, digits, hip, radius, and clavicle, usually resolve spontaneously or are easily managed by the affected individual. Other features include hypotonia with delayed motor development, fatigue and muscle cramps, and easy bruising. Less common findings include mitral and tricuspid valve prolapse, aortic root dilatation, and spontaneous rupture of large arteries. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1244]
Cockayne syndrome (referred to as CS in this GeneReview) spans a phenotypic spectrum that includes: CS type I, the "classic" or “moderate” form; CS type II, a more severe form with symptoms present at birth; this form overlaps with cerebrooculofacioskeletal syndrome (COFS) or Pena-Shokeir syndrome type II; CS type III, a milder form; Xeroderma pigmentosum-Cockayne syndrome (XP-CS). [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1342]
Myotonia congenita is characterized by muscle stiffness present from childhood; all striated muscle groups including the extrinsic eye muscles, facial muscles, and tongue may be involved. Stiffness is relieved by repeated contractions of the muscle (the “warm-up” phenomenon). Muscles are usually hypertrophic. The autosomal recessive form of myotonia congenita is often associated with more severe symptoms than the autosomal dominant form. Individuals with the autosomal recessive form may have progressive, minor distal weakness and attacks of transient weakness brought on by movement after rest. The age of onset is variable: in autosomal dominant myotonia congenita, onset of symptoms is usually in infancy or early childhood; in the autosomal recessive form, the average age of onset is slightly older. In both, onset may be as late as the third or fourth decade of life. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1355]
SALL4-related disorders include Duane-radial ray syndrome (DRRS, Okihiro syndrome), acro-renal-ocular syndrome (AROS), and SALL4-related Holt-Oram syndrome (HOS), three phenotypes previously thought to be distinct entities: DRRS is characterized by uni- or bilateral Duane anomaly and radial ray malformation that can include thenar hypoplasia and/or hypoplasia or aplasia of the thumbs, hypoplasia or aplasia of the radii, shortening and radial deviation of the forearms, triphalangeal thumbs, and duplication of the thumb (preaxial polydactyly). AROS is characterized by radial ray malformations, renal abnormalities (mild malrotation, ectopia, horseshoe kidney, renal hypoplasia, vesico-ureteral reflux, bladder diverticula), ocular coloboma, and Duane anomaly. Rarely, pathogenic variants in SALL4 may cause clinically typical HOS (i.e., radial ray malformations and cardiac malformations without additional features). [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1373]
X-Linked Severe Combined Immunodeficiency
X-linked severe combined immunodeficiency (X-SCID) is a combined cellular and humoral immunodeficiency caused by pathogenic variants in IL2RG. In typical X-SCID lack of IL2RG function results in near complete absence of T and natural killer (NK) lymphocytes and nonfunctional B lymphocytes. X-SCID is almost universally fatal in the first two years of life unless reconstitution of the immune system is achieved through bone marrow transplant or gene therapy. In the absence of family history of X-SCID and prior to newborn screening for X-SCID, most males with typical X-SCID come to medical attention between ages three and six months. During the first year of life nearly all untreated males with X-SCID exhibit failure to thrive, oral/diaper candidiasis, absent tonsils and lymph nodes, recurrent infections, infections with opportunistic organisms such as Pneumocystis, and persistence of infections despite conventional treatment. Additional common features include rashes, diarrhea, cough and congestion, fevers, pneumonia, sepsis, and other severe bacterial infections. Males with atypical X-SCID may have immune dysregulation and autoimmunity associated with rashes, gastrointestinal malabsorption, and short stature. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1410]
The phenotypic spectrum of L1 syndrome includes:X-linked hydrocephalus with stenosis of the aqueduct of Sylvius (HSAS); MASA syndrome (mental retardation, aphasia [delayed speech], spastic paraplegia [shuffling gait], adducted thumbs); SPG1 (X-linked complicated hereditary spastic paraplegia type 1); and X-linked complicated corpus callosum agenesis. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1484]
Cleidocranial Dysplasia Spectrum Disorder
Cleidocranial dysplasia (referred to as CCD in this review) is a skeletal dysplasia characterized by delayed closure of the cranial sutures, hypoplastic or aplastic clavicles, and multiple dental abnormalities. Manifestations may vary among individuals in the same family. The most prominent clinical findings are abnormally large, wide-open fontanels at birth that may remain open throughout life; mid-face retrusion; abnormal dentition, including delayed eruption of secondary dentition, failure to shed the primary teeth, supernumerary teeth with dental crowding, and malocclusion; clavicular hypoplasia resulting in narrow, sloping shoulders that can be apposed at the midline; and hand abnormalities such as brachydactyly, tapering fingers, and short, broad thumbs. Individuals with CCD are shorter than their unaffected sibs and are more likely to have other skeletal/orthopedic problems such as pes planus, genu valgum, and scoliosis. Other medical problems include recurrent sinus infections and other upper-airway complications, recurrent ear infections, high incidence of cesarean section, and mild degree of motor delay in children under age five years. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1513]
Arterial tortuosity syndrome (ATS) is characterized by: Severe and widespread arterial tortuosity of the aorta and middle-sized arteries (with an increased risk of aneurysms and dissections) and focal and widespread stenosis which can involve the aorta and/or pulmonary arteries; The risk for ischemic vascular events involving cerebrovascular circulation and the abdominal arteries is increased. In addition, large veins may be dilated and valvular regurgitation and mitral valve prolapse can occur. Craniofacial involvement with characteristic facies and high palate with dental crowding; Soft/doughy skin and other evidence of a generalized connective tissue disorder including skeletal findings (scoliosis, pectus excavatum/carinatum, joint laxity, knee/elbow contractures, arachnodactyly, camptodactyly); inguinal/abdominal wall hernia; sliding hiatal or diaphragmatic hernia; hypotonia; and ocular involvement (myopia, keratoconus). [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK253404]
The Pol III-related leukodystrophies, hypomyelinating leukodystrophies with some shared features on brain MRI, are characterized by varying combinations of the three major clinical findings: Motor dysfunction (progressive gait abnormalities due to spasticity, cerebellar ataxia, and/or tremor) Abnormal dentition (delayed dentition, hypodontia, oligodontia, and abnormally placed or shaped teeth) Hypogonadotropic hypogonadism. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK99167]
Pitt-Hopkins syndrome (PTHS) is characterized by distinctive facial features which become more apparent with age (100%), developmental delay/intellectual disability (100%), and episodic hyperventilation and/or breath-holding while awake (55%-60%). Global developmental delays are significant and intellectual disability is moderate to severe: mean age of walking is four to six years; most affected individuals are nonverbal. Other common findings are behavioral issues, hand stereotypic movements, seizures (40%-50%), constipation, and severe myopia. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK100240]
Familial pulmonary fibrosis (FPF in this GeneReview) is defined as idiopathic interstitial pneumonia (IIP) in two or more first-degree relatives (parent, sib, or offspring). Up to 20% of cases of IIP cluster in families. The clinical findings of IIP are bibasilar reticular abnormalities, ground glass opacities, or diffuse nodular lesions on high-resolution computed tomography and abnormal pulmonary function studies that include evidence of restriction (reduced VC with an increase in FEV1/FVC ratio) and/or impaired gas exchange (increased P(A-a)O2 with rest or exercise or decreased diffusion capacity of the lung for carbon monoxide [DLCO]). FPF usually presents between ages 50 and 70 years. FPF may be complicated by lung cancer; bronchoalveolar cell carcinoma, small-cell carcinoma, and adenocarcinoma have been described. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1230]
X-Linked Sideroblastic Anemia and Ataxia
X-linked sideroblastic anemia and ataxia (XLSA/A) is characterized by moderate anemia and early-onset spinocerebellar syndrome in males, manifest primarily as delayed walking, ataxia evident in early childhood, dysmetria, and dysdiadochokinesis. When present the intention tremor is mild and the dysarthria is mild to moderately severe. The ataxia has been described to be either non-progressive or slowly progressive. Upper motor neuron (UMN) signs in the legs, manifest by brisk deep tendon reflexes, unsustained ankle clonus, and equivocal or extensor plantar responses, are present in some males. Need for crutches or a wheelchair has been reported. Strabismus is seen in some males. Nystagmus and hypometric saccades may occur. Mild learning disability and depression are seen. The moderate hypochromic and microcytic anemia does not cause symptoms. Carrier (heterozygous) females have a normal neurologic examination and may show mild hematologic abnormalities. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1321]
NR0B1-Related Adrenal Hypoplasia Congenita
X-linked adrenal hypoplasia congenita (X-linked AHC) is characterized by infantile-onset acute primary adrenal insufficiency at an average age of three weeks in approximately 60% of affected individuals. Onset in approximately 40% is in childhood. A few individuals present in adulthood with delayed-onset adrenal failure or partial hypogonadism due to partial forms of X-linked AHC. Adrenal insufficiency typically presents acutely in male infants with vomiting, feeding difficulty, dehydration, and shock caused by a salt-wasting episode. Hypoglycemia (sometimes presenting with seizures) or isolated salt loss may be the first symptom of X-linked AHC. Cortisol may be low or within the normal range, which is inappropriately low for a sick child. In older children, adrenal failure may be precipitated by intercurrent illness or stress. If untreated, adrenal insufficiency is rapidly lethal as a result of hyperkalemia, acidosis, hypoglycemia, and shock. Affected males typically have delayed puberty (onset age >14 years) or arrested puberty caused by hypogonadotropic hypogonadism (HH). Early pubertal development with pubertal arrest has been reported in some cases. Males with classic X-linked AHC are infertile despite treatment with exogenous gonadotropin therapy or pulsatile gonadotropin-releasing hormone (GnRH), although testicular sperm extraction-intracytoplasmic sperm injection (TESE-ICSI) has been successful in one case. Carrier females may very occasionally have symptoms of adrenal insufficiency or hypogonadotropic hypogonadism as a result of skewed X-chromosome inactivation. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1431]
Cantú syndrome and the related disorders acromegaloid facial appearance (AFA) and hypertrichosis and acromegaloid facial features (HAFF) are characterized by congenital hypertrichosis; distinctive coarse facial features (including broad nasal bridge, wide mouth with full lips and macroglossia); enlarged heart (increased ventricular mass, enlarged chambers, and normal cardiac function); and skeletal abnormalities (thickening of the calvaria, broad ribs, scoliosis, and flaring of the metaphyses). Other cardiovascular abnormalities may include patent ductus arteriosus (PDA) (in 50%), pericardial effusion (20%), and increased vascular tortuosity. Intellect is typically normal; behavioral problems can include anxiety, mood swings, obsessive-compulsive disorder, and tics. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK246980]
TBC1D24-related disorders comprise a continuum that includes the following recognized phenotypes:DOORS syndrome (deafness, onychodystrophy, osteodystrophy, mental retardation, and seizures): profound sensorineural hearing loss, onychodystrophy, osteodystrophy, intellectual disability/developmental delay, and seizures Familial infantile myoclonic epilepsy (FIME): early-onset myoclonic seizures, focal epilepsy, dysarthria, and mild-to-moderate intellectual disability Progressive myoclonus epilepsy (PME): action myoclonus, tonic-clonic seizures, progressive neurologic decline, and ataxia Early-infantile epileptic encephalopathy 16 (EIEE16): epileptiform EEG abnormalities which themselves are believed to contribute to progressive disturbance in cerebral function Autosomal recessive nonsyndromic hearing loss, DFNB86: profound prelingual deafness Autosomal dominant nonsyndromic hearing loss, DFNA65: slowly progressive deafness with onset in the third decade, initially affecting the high frequencies [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK274566]
Deficiency of argininosuccinate lyase (ASL), the enzyme that cleaves argininosuccinic acid to produce arginine and fumarate in the fourth step of the urea cycle, is characterized by a severe neonatal onset form and a late onset form. The severe neonatal onset form, which is indistinguishable from that of other urea cycle disorders, is characterized by hyperammonemia within the first few days after birth accompanied by vomiting, lethargy, hypothermia, and poor feeding. In the absence of treatment, lethargy, seizures, and coma worsen, resulting in death. In contrast, the late onset form ranges from episodic hyperammonemia triggered by acute infection or stress to cognitive impairment, behavioral abnormalities, and/or learning disabilities in the absence of any documented episodes of hyperammonemia. Manifestations of ASL deficiency that appear to be unrelated to the severity or duration of hyperammonemic episodes include: (1) neurocognitive deficiencies (attention deficit hyperactivity disorder [ADHD], developmental disability, seizures, and learning disability); (2) liver disease (hepatitis, cirrhosis); (3) trichorrhexis nodosa (coarse brittle hair that breaks easily); and (4) systemic hypertension. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK51784]
Familial Paroxysmal Nonkinesigenic Dyskinesia
Familial paroxysmal nonkinesigenic dyskinesia (referred to as familial PNKD in this entry) is characterized by unilateral or bilateral involuntary movements; attacks are spontaneous or precipitated by alcohol, coffee or tea, excitement, stress, fatigue, or chocolate. Attacks involve dystonic posturing with choreic and ballistic movements, may be accompanied by a preceding aura, occur while the individual is awake, and are not associated with seizures. Attacks last minutes to hours and rarely occur more than once per day. Attack frequency, duration, severity, and combinations of symptoms vary within and among families. Age of onset is typically in childhood or early teens, but can be as late as age 50 years. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1221]
Sotos syndrome is characterized by a distinctive facial appearance (broad and prominent forehead, sparse frontotemporal hair, downslanting palpebral fissures, malar flushing, long and narrow face, long chin); learning disability (early developmental delay, mild to severe intellectual impairment); and overgrowth (height and/or head circumference ≥2 SD above the mean). These three clinical features are considered the cardinal features of Sotos syndrome. Major features of Sotos syndrome include behavioral problems, advanced bone age, cardiac anomalies, cranial MRI/CT abnormalities, joint hyperlaxity/pes planus, maternal preeclampsia, neonatal jaundice, neonatal hypotonia, renal anomalies, scoliosis, and seizures. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1479]
Aceruloplasminemia is characterized by iron accumulation in the brain and viscera. The clinical triad of retinal degeneration, diabetes mellitus (DM), and neurologic disease is seen in individuals ranging from age 25 years to older than 70 years. The neurologic findings of movement disorder (blepharospasm, grimacing, facial and neck dystonia, tremors, chorea) and ataxia (gait ataxia, dysarthria) correspond to regions of iron deposition in the brain. Individuals with aceruloplasminemia often present with anemia prior to onset of DM or obvious neurologic problems. Cognitive dysfunction including apathy and forgetfulness occurs in more than half of individuals with this condition. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1493]
Rubinstein-Taybi syndrome (RSTS) is characterized by distinctive facial features, broad and often angulated thumbs and great toes, short stature, and moderate to severe intellectual disability. The characteristic craniofacial features are downslanted palpebral fissures, low hanging columella, high palate, grimacing smile, and talon cusps. Prenatal growth is often normal; however, height, weight, and head circumference percentiles rapidly drop in the first few months of life. Obesity may occur in childhood or adolescence. IQ scores range from 25 to 79; average IQ is between 36 and 51. Other variable findings are coloboma, cataract, congenital heart defects, renal abnormalities, and cryptorchidism. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1526]
Congenital erythropoietic porphyria (CEP) is characterized in most individuals by severe cutaneous photosensitivity at birth or in early infancy with blistering and increased friability of the skin over light-exposed areas. The first manifestation is often pink to dark red discoloration of the urine. Hemolytic anemia is common and can range from mild to severe, with some affected individuals requiring chronic blood transfusions. Porphyrin deposition may lead to corneal ulcers and scarring, reddish-brown color of the teeth (erythrodontia), and mild bone loss and/or expansion of the bone marrow. The phenotypic spectrum, however, is broad, ranging from non-immune hydrops fetalis in utero to late-onset disease with only mild cutaneous manifestations in adulthood. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK154652]
EPB42-related hereditary spherocytosis (EPB42-HS) is a chronic non-immune hemolytic anemia that is usually of mild to moderate severity. EPB42-HS can present with jaundice as early as the first 24 hours of life or can present later in childhood with anemia resulting from a hemolytic crisis or aplastic crisis (usually associated with a viral infection). In addition to the hematologic manifestations, serious complications include splenomegaly that can become evident in early childhood and cholelithiasis that usually becomes evident in the second or third decade of life. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK190102]
The phenotypic spectrum of lysosomal acid lipase (LAL) deficiency ranges from the infantile-onset form (Wolman disease) to later-onset forms collectively known as cholesterol ester storage disease (CESD). [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK305870]
Cold-Induced Sweating Syndrome including Crisponi Syndrome
Crisponi syndrome, the infantile presentation of cold-induced sweating syndrome (CISS), is characterized by dysmorphic features (distinctive facies, lower facial weakness, flexion deformity at the elbows, camptodactyly with fisted hands, misshapen feet, and overriding toes), poor suck reflex and severely impaired swallowing, temperature spikes not associated with infections, and increased risk for seizures and sudden death. During the first decade of life, children with CISS develop profuse sweating of the face, arms, and chest with ambient temperatures below 18º to 22º C and often with other stimuli including apprehension or ingestion of sweets. Affected individuals sweat very little in hot environments and may feel overheated. In the second decade, progressive thoracolumbar kyphoscoliosis requires intervention. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK52917]
Mitochondrial Neurogastrointestinal Encephalopathy Disease
Mitochondrial neurogastrointestinal encephalopathy (MNGIE) disease is characterized by progressive gastrointestinal dysmotility and cachexia manifesting as early satiety, nausea, dysphagia, gastroesophageal reflux, postprandial emesis, episodic abdominal pain and/or distention, and diarrhea; ptosis/ophthalmoplegia or ophthalmoparesis; hearing loss; and demyelinating peripheral neuropathy manifesting as paresthesias (tingling, numbness, and pain) and symmetric and distal weakness more prominently affecting the lower extremities. The order in which manifestations appear is unpredictable. Onset is usually between the first and fifth decades; in about 60% of individuals, symptoms begin before age 20 years. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1179]
Classic Saethre-Chotzen syndrome (SCS) is characterized by coronal synostosis (unilateral or bilateral), facial asymmetry (particularly in individuals with unilateral coronal synostosis), ptosis, and characteristic appearance of the ear (small pinna with a prominent crus). Syndactyly of digits two and three of the hand is variably present. Intelligence is usually normal, although those with large genomic deletions are more likely to have developmental delays. Less common manifestations of SCS include short stature, parietal foramina, vertebral fusions, radioulnar synostosis, cleft palate, maxillary hypoplasia, ocular hypertelorism, hallux valgus, duplicated distal hallucal phalanx, and congenital heart malformations. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1189]
Phelan-McDermid syndrome (22q13.3 deletion syndrome) is characterized by neonatal hypotonia, global developmental delay, absent to severely delayed speech, and normal to accelerated growth. Most individuals have moderate to profound intellectual disability. Other features include large fleshy hands, dysplastic toenails, and decreased perspiration that results in a tendency to overheat. Behavior characteristics include mouthing or chewing non-food items, decreased perception of pain, and autistic-like affect. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1198]
Dysferlinopathy includes a spectrum of muscle disease characterized by two main phenotypes: Miyoshi myopathy with primarily distal weakness and limb-girdle muscular dystrophy type 2B (LGMD2B) with primarily proximal weakness. Miyoshi myopathy (median age of onset 19 years) is characterized by muscle weakness and atrophy, most marked in the distal parts of the legs, especially the gastrocnemius and soleus muscles. Over a period of years, the weakness and atrophy spread to the thighs and gluteal muscles. The forearms may become mildly atrophic with decrease in grip strength; the small muscles of the hands are spared. LGMD2B is characterized by early weakness and atrophy of the pelvic and shoulder girdle muscles in adolescence or young adulthood, with slow progression. Other phenotypes are scapuloperoneal syndrome, distal myopathy with anterior tibial onset, elevated serum CK concentration only, and congenital muscular dystrophy. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1303]
Hereditary Sensory and Autonomic Neuropathy Type II
Hereditary sensory and autonomic neuropathy type II (HSAN2) is characterized by progressively reduced sensation to pain, temperature, and touch. Onset can be at birth and is often before puberty. The sensory deficit is predominantly distal with the lower limbs more severely affected than the upper limbs. Over time sensory function becomes severely reduced. Unnoticed injuries and neuropathic skin promote ulcerations and infections that result in spontaneous amputation of digits or the need for surgical amputation. Osteomyelitis is common. Painless fractures can complicate the disease. Autonomic disturbances are variable and can include hyperhidrosis, tonic pupils, and urinary incontinence in those with more advanced disease. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK49247]
Caffey disease is characterized by massive subperiosteal new bone formation (usually involving the diaphyses of the long bones as well as the ribs, mandible, scapulae, and clavicles) typically associated with fever, joint swelling, and pain in children, with onset around age two months and spontaneous resolution by age two years. On rare occasion, the hyperostosis can be detected by ultrasound examination late in the third trimester of pregnancy. Limited follow-up information suggests that adults who had Caffey disease in childhood may manifest joint laxity, skin hyperextensibility, hernias, and an increased risk for bone fractures and/or deformities. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK99168]
Familial Exudative Vitreoretinopathy, Autosomal Dominant
Autosomal dominant familial exudative vitreoretinopathy (adFEVR) is characterized by failure of peripheral retinal vascularization. The visual problems and variable phenotype associated with adFEVR result from secondary complications caused by retinal ischemia. The retinal avascularity is probably present from birth and generates sequelae that stabilize in early adult life or progress in later life. Expressivity may be asymmetric and is highly variable, ranging from mild or asymptomatic to severe (e.g., registered as blind) within the same family. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1147]
Marfan syndrome is a systemic disorder of connective tissue with a high degree of clinical variability. Cardinal manifestations involve the ocular, skeletal, and cardiovascular systems. FBN1 pathogenic variants associate with a broad phenotypic continuum, ranging from isolated features of Marfan syndrome to neonatal presentation of severe and rapidly progressive disease in multiple organ systems. Myopia is the most common ocular feature; displacement of the lens from the center of the pupil, seen in approximately 60% of affected individuals, is a hallmark feature. People with Marfan syndrome are at increased risk for retinal detachment, glaucoma, and early cataract formation. The skeletal system involvement is characterized by bone overgrowth and joint laxity. The extremities are disproportionately long for the size of the trunk (dolichostenomelia). Overgrowth of the ribs can push the sternum in (pectus excavatum) or out (pectus carinatum). Scoliosis is common and can be mild or severe and progressive. The major sources of morbidity and early mortality in the Marfan syndrome relate to the cardiovascular system. Cardiovascular manifestations include dilatation of the aorta at the level of the sinuses of Valsalva, a predisposition for aortic tear and rupture, mitral valve prolapse with or without regurgitation, tricuspid valve prolapse, and enlargement of the proximal pulmonary artery. With proper management, the life expectancy of someone with Marfan syndrome approximates that of the general population. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1335]
Charcot-Marie-Tooth neuropathy type 4C (CMT4C) is a demyelinating neuropathy characterized by early-onset severe spine deformities. The majority of affected children present with scoliosis or kyphoscoliosis between ages two and ten years, although earlier and later onset are observed. Slowly progressive neuropathy usually manifests in the first decade or adolescence, and occasionally earlier or later. Foot deformities (pes cavus, pes planus, or pes valgus) are common. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1340]
Thanatophoric dysplasia (TD) is a short-limb dwarfism syndrome that is usually lethal in the perinatal period. TD is divided into type I, characterized by micromelia with bowed femurs and, uncommonly, the presence of cloverleaf skull deformity (Kleeblattschädel) of varying severity; and type II, characterized by micromelia with straight femurs and uniform presence of moderate-to-severe cloverleaf skull deformity. Other features common to type I and type II include: short ribs, narrow thorax, macrocephaly, distinctive facial features, brachydactyly, hypotonia, and redundant skin folds along the limbs. Most affected infants die of respiratory insufficiency shortly after birth. Rare long-term survivors have been reported. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1366]
Juvenile polyposis syndrome (JPS) is characterized by predisposition to hamartomatous polyps in the gastrointestinal (GI) tract, specifically in the stomach, small intestine, colon, and rectum. The term "juvenile" refers to the type of polyp rather than to the age of onset of polyps. Most individuals with JPS have some polyps by age 20 years; some may have only four or five polyps over their lifetime, whereas others in the same family may have more than a hundred. If the polyps are left untreated, they may cause bleeding and anemia. Most juvenile polyps are benign; however, malignant transformation can occur. Risk for GI cancers in families with JPS ranges from 9% to 50%. Most of this increased risk is attributed to colon cancer, but cancers of the stomach, upper GI tract, and pancreas have also been reported. A combined syndrome of JPS and hereditary hemorrhagic telangiectasia (HHT) (termed JPS/HHT) is present in most individuals with an SMAD4 pathogenic variant. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1469]
Cohen syndrome is characterized by failure to thrive in infancy and childhood; truncal obesity in the teen years; early-onset hypotonia and developmental delays; microcephaly developing during the first year of life; moderate to profound psychomotor retardation; progressive retinochoroidal dystrophy and high myopia; neutropenia in many with recurrent infections and aphthous ulcers in some; a cheerful disposition; joint hypermobility; and characteristic facial features. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1482]
The phenotypic spectrum of mucopolysaccharidosis IVA (MPS IVA) is a continuum that ranges from a severe and rapidly progressive early-onset form to a slowly progressive later-onset form. Children with MPS IVA have no distinctive clinical findings at birth. The severe form is usually apparent between ages one and three years, often first manifesting as kyphoscoliosis, knock-knee (genu valgum), and pectus carinatum; the slowly progressive form may not become evident until late childhood or adolescence often first manifesting as hip problems (pain, stiffness, and Legg Perthes disease). Progressive bone and joint involvement leads to short stature, and pain and arthritis that become disabling. Involvement of other organ systems can lead to significant morbidity, including respiratory compromise, obstructive sleep apnea, valvular heart disease, hearing impairment, visual impairment from corneal clouding, dental abnormalities, and hepatomegaly. Compression of the spinal cord is a common complication that results in neurologic impairment. Children with MPS IVA have normal intellectual abilities at the outset of the disease. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK148668]
Hereditary folate malabsorption (HFM) is characterized by folate deficiency with impaired intestinal folate absorption and impaired folate transport into the central nervous system (CNS). Findings include poor feeding and failure to thrive, anemia often accompanied by leukopenia and/or thrombocytopenia, diarrhea and/or oral mucositis, hypoimmunoglobulinemia, and other immunologic dysfunction resulting in infections with unusual organisms. Neurologic manifestations include developmental delays, cognitive and motor impairment, behavioral disorders and, frequently, seizures. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1673]
Spinocerebellar ataxia type 6 (SCA6) is characterized by adult-onset, slowly progressive cerebellar ataxia, dysarthria, and nystagmus. Mean age of onset is 43 to 52 years. Initial symptoms are gait unsteadiness, stumbling, and imbalance (in ~90%) and dysarthria (in ~10%). Eventually all persons have gait ataxia, upper-limb incoordination, intention tremor, and dysarthria. Dysphagia and choking are common. Visual disturbances may result from diplopia, difficulty fixating on moving objects, horizontal gaze-evoked nystagmus, and vertical nystagmus. Hyperreflexia and extensor plantar responses occur in up to 40%-50%. Basal ganglia signs, including dystonia and blepharospasm, occur in up to 25%. Mentation is generally preserved. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1140]
Succinic Semialdehyde Dehydrogenase Deficiency
Succinic semialdehyde dehydrogenase (SSADH) deficiency is characterized by psychomotor retardation, childhood-onset hypotonia, and ataxia. Seizures occur in more than 50% of affected individuals. Hyperkinetic behavior, aggression, self-injurious behaviors, hallucinations, and sleep disturbances have been reported in nearly half of all patients, and are common in older individuals. Basal ganglia signs such as choreoathetosis, dystonia, and myoclonus have been reported in a few individuals with earlier-onset, more severe disease. Involvement beyond the central nervous system has not been described. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1195]
Neurodegeneration with Brain Iron Accumulation Disorders Overview
Neurodegeneration with brain iron accumulation (NBIA) is a group of inherited neurologic disorders in which iron accumulates in the basal ganglia resulting in progressive dystonia, spasticity, parkinsonism, neuropsychiatric abnormalities, and optic atrophy or retinal degeneration. Ten types and their associated genes are recognized. The age of onset ranges from infancy to late adulthood; the rate of progression varies. Cognitive decline occurs in some subtypes, but more often cognition is relatively spared. Cerebellar atrophy is a frequent finding in some subtypes. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK121988]
Diastrophic dysplasia (DTD) is characterized by limb shortening, normal-sized skull, hitchhiker thumbs, spinal deformities (scoliosis, exaggerated lumbar lordosis, cervical kyphosis), and contractures of the large joints with deformities and early-onset osteoarthritis. Other typical findings are ulnar deviation of the fingers, gap between the first and second toes, and clubfoot. On occasion the disease can be lethal at birth, but most affected individuals survive the neonatal period and develop physical limitations with normal intelligence. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1350]
Autosomal Dominant Tubulointerstitial Kidney Disease, UMOD-Related
UMOD-associated kidney disease (uromodulin-associated kidney disease) is also known as familial juvenile hyperuricemic nephropathy type 1 (FJHN1) and medullary cystic kidney disease type 2 (MCKD2). Clinical findings typically include hyperuricemia and gout (resulting from reduced kidney excretion of uric acid) that usually occur as early as the teenage years. Slowly progressive interstitial kidney disease begins early in life. Elevations in serum creatinine usually occur between ages five and 40 years, leading to end-stage kidney disease (ESRD) usually between the fourth and seventh decade. The age at ESRD varies both between and within families. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1356]
Cytochrome P450 Oxidoreductase Deficiency
Cytochrome P450 oxidoreductase (POR) deficiency is a disorder of steroidogenesis with a phenotypic spectrum ranging from cortisol deficiency at the milder end to classic Antley-Bixler syndrome (ABS) at the severe end. Cortisol deficiency can range from clinically insignificant to life threatening; manifestations can include ambiguous genitalia in both males and females; primary amenorrhea and enlarged cystic ovaries in females; poor masculinization during puberty in males; and maternal virilization during pregnancy with an affected fetus. Manifestations of ABS include craniosynostosis; hydrocephalus; distinctive facies; choanal stenosis or atresia; low-set dysplastic ears with stenotic external auditory canals; skeletal anomalies (radiohumeral synostosis, neonatal fractures, congenital bowing of the long bones, joint contractures, arachnodactyly, clubfeet); renal anomalies (ectopic kidneys, duplication of the kidneys, renal hypoplasia, horseshoe kidney, hydronephrosis); and reduction of cognitive function and developmental delay. In moderate POR deficiency, craniofacial and skeletal anomalies are less severe than in ABS. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1419]
Ataxia with oculomotor apraxia type 1 (AOA1) is characterized by childhood onset of slowly progressive cerebellar ataxia, followed by oculomotor apraxia and a severe primary motor peripheral axonal motor neuropathy. The first manifestation is progressive gait imbalance (mean age of onset: 4.3 years; range: 2-10 years), followed by dysarthria, then upper-limb dysmetria with mild intention tremor. Oculomotor apraxia, usually noticed a few years after the onset of ataxia, progresses to external ophthalmoplegia. All affected individuals have generalized areflexia followed by a peripheral neuropathy and quadriplegia with loss of ambulation about seven to ten years after onset. Hands and feet are short and atrophic. Chorea and upper-limb dystonia are common. Intellect remains normal in some individuals; in others, different degrees of cognitive impairment have been observed. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1456]
Pseudoachondroplasia is characterized by normal length at birth and normal facies. Often the presenting feature is a waddling gait, recognized at the onset of walking. Typically, the growth rate falls below the standard growth curve by approximately age two years, leading to a moderately severe form of disproportionate short-limb short stature. Joint pain during childhood, particularly in the large joints of the lower extremities, is common. Degenerative joint disease is progressive; approximately 50% of individuals with pseudoachondroplasia eventually require hip replacement surgery. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1487]
Dentatorubral-pallidoluysian atrophy (DRPLA) is a progressive disorder of ataxia, choreoathetosis, and dementia or character changes in adults and ataxia, myoclonus, epilepsy, and progressive intellectual deterioration in children. The age of onset is from one to 62 years with a mean age of onset of 30 years. The clinical presentation varies depending on the age of onset. The cardinal features in adults are ataxia, choreoathetosis, and dementia. Cardinal features in children are progressive intellectual deterioration, behavioral changes, myoclonus, and epilepsy. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1491]
LMNA-related dilated cardiomyopathy (DCM) is caused by mutations in LMNA and is characterized by left ventricular enlargement and reduced systolic function preceded or accompanied by significant conduction system disease and/or arrhythmias. LMNA-related DCM usually presents in early to mid-adulthood with symptomatic conduction system disease or arrhythmias, or with symptomatic DCM including heart failure or embolus from a left ventricular mural thrombus. Sudden cardiac death can occur, and in some instances is the presenting manifestation; sudden cardiac death may occur with little systolic dysfunction. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1674]
The phenotypic spectrum of sepiapterin reductase deficiency (SRD), which ranges from significant motor and cognitive deficits to only minimal findings, has not been completely elucidated. Clinical features in the majority of affected individuals include motor and speech delay, axial hypotonia, dystonia, weakness, and oculogyric crises; symptoms show diurnal fluctuation and sleep benefit. Other common features include parkinsonian signs (tremor, bradykinesia, masked facies, rigidity), limb hypertonia, hyperreflexia, intellectual disability, psychiatric and/or behavioral abnormalities, autonomic dysfunction, and sleep disturbances (hypersomnolence, difficulty initiating or maintaining sleep, and drowsiness). Most affected individuals have nonspecific features in infancy including developmental delays and axial hypotonia; other features develop over time. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK304122]
The spectrum of propionic acidemia (PA) ranges from neonatal-onset to late-onset disease.Neonatal-onset PA, the most common form, is characterized by poor feeding, vomiting, and somnolence in the first days of life in a previously healthy infant, followed by lethargy, seizures, coma, and death. It is frequently accompanied by metabolic acidosis with anion gap, ketonuria, hypoglycemia, hyperammonemia, and cytopenias. Late-onset PA includes developmental regression, chronic vomiting, protein intolerance, failure to thrive, hypotonia, and occasionally basal ganglia infarction (resulting in dystonia and choreoathetosis) and cardiomyopathy. Affected children can have an acute decompensation that resembles the neonatal presentation and is precipitated by a catabolic stress such as infection, injury, or surgery. Isolated cardiomyopathy and arrhythmia can be observed on rare occasion in the absence of clinical metabolic decompensation or neurocognitive deficits. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK92946]
Spastic paraplegia 11 (SPG11) is characterized by progressive spasticity and weakness of the lower limbs frequently associated with the following: mild intellectual disability with learning difficulties in childhood and/or progressive cognitive decline; peripheral neuropathy; pseudobulbar involvement; and increased reflexes in the upper limbs. Less frequent findings include: cerebellar signs (ataxia, nystagmus, saccadic pursuit); retinal degeneration; pes cavus; scoliosis; and parkinsonism. Onset occurs mainly during infancy or adolescence (range: age 1-31 years). Most affected individuals become wheelchair bound one or two decades after disease onset. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1210]
Schimke immunoosseous dysplasia (SIOD) is an autosomal recessive multisystem disorder characterized by spondyloepiphyseal dysplasia (SED) resulting in short stature, nephropathy, and T-cell deficiency. Radiographic manifestations of SED include ovoid and mildly flattened vertebral bodies, small deformed capital femoral epiphyses, and shallow dysplastic acetabular fossae. Adult height is 136-157 cm for men and 98.5-143 cm for women. Nearly all affected individuals have progressive steroid-resistant nephropathy, usually developing within five years of the diagnosis of growth failure and terminating with end-stage renal disease (ESRD). The majority of tested individuals have T-cell deficiency and associated risk for opportunistic infection, a common cause of death. SIOD involves a spectrum that ranges from an infantile or severe early-onset form with death early in life to a juvenile or milder later-onset form with survival into adulthood if renal disease is appropriately treated. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1376]
Diabetes Mellitus, 6q24-Related Transient Neonatal
6q24-related transient neonatal diabetes mellitus (6q24-TNDM) is defined as transient neonatal diabetes mellitus caused by genetic aberrations of the imprinted locus at 6q24. The cardinal features are: severe intrauterine growth retardation, hyperglycemia that begins in the neonatal period in a term infant and resolves by age 18 months, dehydration, and absence of ketoacidosis. Macroglossia and umbilical hernia are often present. In the subset of children with ZFP57 pathogenic variants, other manifestations can include structural brain abnormalities, developmental delay, and congenital heart disease. Diabetes mellitus usually starts within the first week of life and lasts on average three months but can last longer than a year. Although insulin is usually required initially, the need for insulin gradually declines over time. Intermittent episodes of hyperglycemia may occur in childhood, particularly during intercurrent illnesses. Diabetes mellitus may recur in adolescence or later in adulthood. Women who have had 6q24-TNDM are at risk for relapse during pregnancy. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1534]
Dihydrolipoamide Dehydrogenase Deficiency
The phenotypes of dihydrolipoamide dehydrogenase (DLD) deficiency are an overlapping continuum that ranges from early-onset neurologic manifestations to adult-onset isolated liver involvement. Early-onset DLD deficiency typically manifests as a hypotonic infant with lactic acidosis. Affected infants frequently do not survive their initial metabolic decompensation, or die within the first few years of life during a recurrent metabolic decompensation. Children who live beyond the first two to three years frequently exhibit growth deficiencies and residual neurologic deficits (intellectual disability, spasticity, ataxia, and seizures). In contrast, isolated liver involvement can present as early as the neonatal period and as late as the third decade. Evidence of liver injury/failure is preceded by nausea and emesis and frequently associated with encephalopathy and/or coagulopathy. Acute metabolic episodes are frequently associated with lactate elevations, hyperammonemia, and hepatomegaly. With resolution of the acute episodes patients frequently return to baseline with no residual neurologic deficit or intellectual disability. Liver failure can result in death, even in those with late-onset disease. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK220444]
Spinocerebellar ataxia type 36 (SCA36) is characterized by a late-onset, slowly progressive cerebellar syndrome typically associated with sensorineural hearing loss. Other common features are muscle atrophy and denervation, especially of the tongue, as well as pyramidal signs, thus overlapping with motor neuron disorders. Mild frontal-subcortical affective and cognitive decline may be present as the disease progresses. Brain MRI shows atrophy of the cerebellar vermis in initial stages, later evolving to a pattern of olivopontocerebellar atrophy. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK231880]
C9orf72-Related Amyotrophic Lateral Sclerosis and Frontotemporal Dementia
C9orf72-related amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) is characterized by: Motor neuron disease, including upper or lower motor neuron dysfunction (or both) that may or may not fulfill criteria for the ALS phenotype; Frontotemporal lobar degeneration (FTLD), including progressive changes in behavior, executive dysfunction, and/or language impairment; and Some degree of parkinsonism (typically of the akinetic-rigid type without tremor that is levodopa unresponsive). [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK268647]
Optic atrophy type 1 (OPA1, or Kjer type optic atrophy) is characterized by bilateral and symmetric optic nerve pallor associated with insidious decrease in visual acuity (usually between ages 4 and 6 years), visual field defects, and color vision defects. Visual impairment is usually moderate (6/10 to 2/10), but ranges from mild or even insignificant to severe (legal blindness with acuity <1/20). The visual field defect is typically centrocecal, central, or paracentral; it is often large in those with severe disease. The color vision defect is often described as acquired blue-yellow loss (tritanopia). Other findings can include auditory neuropathy resulting in sensorineural hearing loss that ranges from severe and congenital to subclinical (i.e., identified by specific audiologic testing only). [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1248]
Alström syndrome is characterized by cone-rod dystrophy, obesity, progressive sensorineural hearing impairment, dilated or restrictive cardiomyopathy, the insulin resistance syndrome, and multiple organ failure. Wide clinical variability is observed among affected individuals, even within the same family. Cone-rod dystrophy presents as progressive visual impairment, photophobia, and nystagmus usually starting between birth and age 15 months. Many individuals lose all perception of light by the end of the second decade, but a minority retain the ability to read large print into the third decade. Children usually have normal birth weight but develop truncal obesity during their first year. Progressive sensorineural hearing loss presents in the first decade in as many as 70% of individuals. Hearing loss may progress to the severe or moderately severe range (40-70 db) by the end of the first to second decade. Insulin resistance is typically accompanied by the skin changes of acanthosis nigricans, and proceeds to type 2 diabetes in the majority by the third decade. Nearly all demonstrate associated dyslipidemia. Other endocrine abnormalities can include hypothyroidism, hypogonadotropic hypogonadism in boys, and polycystic ovaries in girls. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1267]
Mucopolysaccharidosis type II (MPS II; also known as Hunter syndrome) is an X-linked multisystem disorder characterized by glycosaminoglycans (GAG) accumulation. The vast majority of affected individuals are male; on rare occasion heterozygous females manifest findings. Age of onset, disease severity, and rate of progression vary significantly among affected males. In those with early progressive disease, CNS involvement (manifest primarily by progressive cognitive deterioration), progressive airway disease, and cardiac disease usually result in death in the first or second decade of life. In those with slowly progressive disease, the CNS is not (or is minimally) affected, although the effect of GAG accumulation on other organ systems may be early progressive to the same degree as in those who have progressive cognitive decline. Survival into the early adult years with normal intelligence is common in the slowly progressing form of the disease. Additional findings in both forms of MPS II include: short stature; macrocephaly with or without communicating hydrocephalus; macroglossia; hoarse voice; conductive and sensorineural hearing loss; hepato-splenomegaly; dysostosis multiplex; spinal stenosis; and carpal tunnel syndrome. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1274]
Spinocerebellar ataxia type 2 (SCA2) is characterized by progressive cerebellar ataxia, including nystagmus, slow saccadic eye movements and, in some individuals, ophthalmoparesis or parkinsonism. Pyramidal findings are present; deep tendon reflexes are brisk early on and absent later in the course. Age of onset is typically in the fourth decade with a ten- to 15-year disease duration. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1275]
Sitosterolemia is characterized by: Tendon xanthomas or tuberous (i.e., planar) xanthomas that can occur in childhood and in unusual locations (heels, knees, elbows and buttocks); Premature atherosclerosis which can lead to angina, aortic valve involvement, myocardial infarction, and sudden death; Hemolytic anemia, abnormally shaped erythrocytes (stomatocytes), and large platelets (macrothrombocytopenia). [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK131810]
Spinocerebellar ataxia type 14 (SCA14) is characterized by slowly progressive cerebellar ataxia, dysarthria, and nystagmus. Axial myoclonus, cognitive impairment, tremor, and sensory loss may also be observed. Parkinsonian features including rigidity and tremor have been described in some families. Findings seen in other ataxia disorders (e.g., dysphagia, dysphonia) may also occur in SCA14. Age of onset ranges from childhood to the sixth decade. Life span is not shortened. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1399]
Lowe syndrome (oculocerebrorenal syndrome) is characterized by involvement of the eyes, central nervous system, and kidneys. Dense congenital cataracts are found in all affected boys and infantile glaucoma in approximately 50%. All boys have impaired vision; corrected acuity is rarely better than 20/100. Generalized hypotonia is noted at birth and is of central (brain) origin. Deep tendon reflexes are usually absent. Hypotonia may slowly improve with age, but normal motor tone and strength are never achieved. Motor milestones are delayed. Almost all affected males have some degree of intellectual disability; 10%-25% function in the low-normal or borderline range, approximately 25% in the mild-to-moderate range, and 50%-65% in the severe-to-profound range of intellectual disability. Affected males have varying degrees of proximal renal tubular dysfunction of the Fanconi type, including bicarbonate wasting and renal tubular acidosis, phosphaturia with hypophosphatemia and renal rickets, aminoaciduria, low molecular-weight (LMW) proteinuria, sodium and potassium wasting, and polyuria. Fanconi syndrome is usually not clinically apparent in the first few months of life, but symptoms may appear by age six to 12 months. Glomerulosclerosis associated with chronic tubular injury usually results in slowly progressive chronic renal failure and end-stage renal disease after age ten to 20 years. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1480]
MYH9-related disorders (MYH9RD) are characterized by large platelets (i.e., >40% of platelets >3.9 μm in diameter) and thrombocytopenia (platelet count <150 x 109/L), both of which are present from birth. MYH9RD is variably associated with young-adult onset of progressive sensorineural hearing loss, presenile cataract, elevation of liver enzymes, and renal disease manifesting initially as glomerular nephropathy. Before identification of the gene in which mutation is causative, MYH9, individuals with MYH9RD were diagnosed as having Epstein syndrome, Fechtner syndrome, May-Hegglin anomaly, or Sebastian syndrome based on the combination of different clinical findings at the time of diagnosis. However, the realization that they all are due to heterozygous pathogenic variants in MYH9 and that the clinical findings often worsen throughout life as a result of late onset of non-hematologic manifestations has led the four conditions to be regarded as one disorder, now known as MYH9RD. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK2689]
AIP-Related Familial Isolated Pituitary Adenomas
AIP-related isolated familial pituitary adenoma (AIP-related FIPA) is defined as the presence of an AIP germline pathogenic variant in an individual with a pituitary adenoma (regardless of family history). [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK97965]
Hypohidrotic ectodermal dysplasia (HED) is characterized by hypotrichosis (sparseness of scalp and body hair), hypohidrosis (reduced ability to sweat), and hypodontia (congenital absence of teeth). The cardinal features of HED become obvious during childhood. The scalp hair is thin, lightly pigmented, and slow-growing. Sweating, although present, is greatly deficient, leading to episodes of hyperthermia until the affected individual or family acquires experience with environmental modifications to control temperature. Only a few abnormally formed teeth erupt, and at a later than average age. Physical growth and psychomotor development are otherwise within normal limits. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1112]
Primary congenital glaucoma (PCG) is characterized by elevated intraocular pressure (IOP), enlargement of the globe (buphthalmos), edema, and opacification of the cornea with rupture of Descemet's membrane (Haabs striae), thinning of the anterior sclera and iris atrophy, anomalously deep anterior chamber, and structurally normal posterior segment except for progressive glaucomatous optic atrophy. Symptoms include photophobia, blepharospasm, and excessive tearing (hyperlacrimation). Typically, the diagnosis is made in the first year of life. Depending on when treatment is instituted, visual acuity may be reduced and/or visual fields may be restricted. In untreated cases, blindness invariably occurs. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1135]
FLNA-Related Periventricular Nodular Heterotopia
FLNA-related periventricular nodular heterotopia (PVNH), a neuronal migration disorder, is characterized by the presence of uncalcified nodules of neurons ectopically situated along the surface of the lateral ventricles. Affected individuals are predominantly heterozygous females; males most often show early lethality. Affected females present with seizures at an average age of 14-15 years; intelligence ranges from normal to borderline. The risk for cardiovascular disease, stroke, and other vascular/coagulation problems appears to be increased. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1213]
Thiamine-Responsive Megaloblastic Anemia Syndrome
Thiamine-responsive megaloblastic anemia syndrome (TRMA) is characterized by megaloblastic anemia, sensorineural hearing loss, and diabetes mellitus. Onset of megaloblastic anemia is between infancy and adolescence. The anemia is corrected with pharmacologic doses of thiamine (vitamin B1) (25-75 mg/day compared to US RDA of 1.5 mg/day). However, the red cells remain macrocytic. The anemia can recur when thiamine is withdrawn. Progressive sensorineural hearing loss has generally been early and can be detected in toddlers; hearing loss is irreversible and may not be prevented by thiamine treatment. The diabetes mellitus is non-type I in nature, with age of onset from infancy to adolescence. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1282]
X-linked lymphoproliferative disease (XLP) is caused by mutations in SH2D1A and XIAP (BIRC4). XLP may also occur in rare instances with no identified underlying genetic cause. The three most commonly recognized phenotypes of SH2D1A-related XLP are hemophagocytic lymphohistiocytosis (HLH) associated with Epstein-Barr virus (EBV) infection (58% of individuals), dysgammaglobulinemia (31%), and lymphoproliferative disorders (malignant lymphoma) (30%). Manifestations of SH2D1A-related XLP, including HLH, can also occur in the absence of EBV. XIAP-related XLP also presents with HLH (often associated with EBV) or dysgammaglobulinemia, but no cases of lymphoma have been described to date. HLH resulting from EBV infection, sometimes referred to as severe infectious mononucleosis, is associated with an unregulated and exaggerated immune response with widespread proliferation of cytotoxic T cells, EBV-infected B cells, and macrophages. Fulminant hepatitis, hepatic necrosis, and profound bone marrow failure are typical, resulting in mortality that is higher than 90%, though prompt recognition of the disorder and aggressive treatment interventions likely improve survival. Dysgammaglobulinemia is typically hypogammaglobulinemia of one or more immunoglobulin subclasses. The prognosis is improved if affected males are managed with regular intravenous immunoglobulin (IVIG) therapy. The malignant lymphomas are typically high-grade B cell lymphomas, non-Hodgkin type, often extranodal, and in particular involving the intestine. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1406]
Nonsyndromic Hearing Loss and Deafness, Mitochondrial
Nonsyndromic mitochondrial hearing loss and deafness is characterized by moderate-to-profound hearing loss and a pathogenic variant in either MT-RNR1 or MT-TS1. Pathogenic variants in MT-RNR1 can be associated with predisposition to aminoglycoside ototoxicity and/or late-onset sensorineural hearing loss. Pathogenic variants in MT-TS1 are usually associated with childhood onset of sensorineural hearing loss. Hearing loss associated with aminoglycoside ototoxicity is bilateral and severe to profound, occurring within a few days to weeks after administration of any amount (even a single dose) of an aminoglycoside antibiotic such as gentamycin, tobramycin, amikacin, kanamycin, or streptomycin. Although hearing loss associated with pathogenic variants in MT-TS1 is considered nonsyndromic, the m.7445A>G substitution is also associated with palmoplantar keratoderma (scaling, hyperkeratosis, and honeycomb appearance of the skin of the palms, soles, and heels) in some families. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1422]
Inclusion Body Myopathy with Paget Disease of Bone and/or Frontotemporal Dementia
Inclusion body myopathy associated with Paget disease of bone (PDB) and/or frontotemporal dementia (IBMPFD) is characterized by adult-onset proximal and distal muscle weakness (clinically resembling a limb-girdle muscular dystrophy syndrome), early-onset PDB, and premature frontotemporal dementia (FTD). Muscle weakness progresses to involve other limb and respiratory muscles. Cardiac failure and cardiomyopathy have been observed in later stages. PDB involves focal areas of increased bone turnover that typically lead to spine and/or hip pain and localized enlargement and deformity of the long bones; pathologic fractures occur on occasion. Early stages of FTD are characterized by dysnomia, dyscalculia, comprehension deficits, paraphasic errors, and relative preservation of memory, and later stages by inability to speak, auditory comprehension deficits for even one-step commands, alexia, and agraphia. Mean age at diagnosis for muscle disease and PDB is 42 years; for FTD, 55 years. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1476]
Hemophilia B is characterized by deficiency in factor IX clotting activity that results in prolonged oozing after injuries, tooth extractions, or surgery, and delayed or recurrent bleeding prior to complete wound healing. The age of diagnosis and frequency of bleeding episodes are related to the level of factor IX clotting activity. In severe hemophilia B, spontaneous joint or deep-muscle bleeding is the most frequent symptom. Individuals with severe hemophilia B are usually diagnosed during the first two years of life; without prophylactic treatment, they may average up to two to five spontaneous bleeding episodes each month. Individuals with moderate hemophilia B seldom have spontaneous bleeding; however, they do have prolonged or delayed oozing after relatively minor trauma and are usually diagnosed before age five to six years; the frequency of bleeding episodes varies from once a month to once a year. Individuals with mild hemophilia B do not have spontaneous bleeding episodes; however, without pre- and post-operative treatment, abnormal bleeding occurs with surgery or tooth extractions; the frequency of bleeding may vary from once a year to once every ten years. Individuals with mild hemophilia B are often not diagnosed until later in life. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1495]
MERRF (myoclonic epilepsy with ragged red fibers) is a multisystem disorder characterized by myoclonus (often the first symptom) followed by generalized epilepsy, ataxia, weakness, and dementia. Onset is usually in childhood, occurring after normal early development. Common findings are hearing loss, short stature, optic atrophy, and cardiomyopathy with Wolff-Parkinson-White (WPW) syndrome. Pigmentary retinopathy and lipomatosis are occasionally observed. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1520]
Pseudohypoaldosteronism type II (PHAII) is characterized by hypertension and hyperkalemia despite normal glomerular filtration rate (GFR). Other associated findings in both children and adults include hyperchloremia, metabolic acidosis, and suppressed plasma renin levels. Aldosterone levels are variable, but are relatively low given the degree of hyperkalemia (elevated serum potassium is a potent stimulus for aldosterone secretion). Hypercalciuria is well described. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK65707]
IPEX (Immune dysregulation, Polyendocrinopathy, Enteropathy, X-linked) syndrome is characterized by systemic autoimmunity, typically beginning in the first year of life. Presentation is most commonly the clinical triad of watery diarrhea, eczematous dermatitis, and endocrinopathy (most commonly insulin-dependent diabetes mellitus). Most children have other autoimmune phenomena including Coombs-positive anemia, autoimmune thrombocytopenia, autoimmune neutropenia, and tubular nephropathy. Without aggressive immunosuppression or bone marrow transplantation, the majority of affected males die within the first one to two years of life from metabolic derangements or sepsis; a few with a milder phenotype have survived into the second or third decade of life. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1118]
Parkinsonism refers to all clinical states characterized by tremor, muscle rigidity, slowed movement (bradykinesia) and often postural instability. Parkinson disease is the primary and most common form of parkinsonism. Psychiatric manifestations, which include depression and visual hallucinations, are common but not uniformly present. Dementia eventually occurs in at least 20% of cases. The most common sporadic form of Parkinson disease manifests around age 60; however, young-onset and even juvenile presentations are seen. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1223]
Stickler syndrome is a connective tissue disorder that can include ocular findings of myopia, cataract, and retinal detachment; hearing loss that is both conductive and sensorineural; midfacial underdevelopment and cleft palate (either alone or as part of the Robin sequence); and mild spondyloepiphyseal dysplasia and/or precocious arthritis. Variable phenotypic expression of Stickler syndrome occurs both within and among families; interfamilial variability is in part explained by locus and allelic heterogeneity. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1302]
The FLNB-related disorders include a spectrum of phenotypes ranging from mild (spondylocarpotarsal synostosis [SCT] syndrome and Larsen syndrome) to severe (atelosteogenesis types I [AOI] and III [AOIII], boomerang dysplasia). [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK2534]
Chediak-Higashi syndrome (CHS) is characterized by partial oculocutaneous albinism (OCA), immunodeficiency, and a mild bleeding tendency. Approximately 85% of affected individuals develop the accelerated phase, a lymphoproliferative infiltration of the bone marrow and reticuloendothelial system. All affected individuals including adolescents and adults with atypical CHS and children with classic CHS who have successfully undergone allogenic hematopoietic stem cell transplantation (HSCT) develop neurologic findings during early adulthood. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK5188]
Duane syndrome is a strabismus syndrome characterized by congenital non-progressive horizontal ophthalmoplegia (inability to move the eyes) primarily affecting the abducens nucleus and nerve and its innervated extraocular muscle, the lateral rectus muscle. At birth, affected infants have restricted ability to move the affected eye(s) outward (abduction) and/or inward (adduction). In addition, the globe retracts into the orbit with attempted adduction, accompanied by narrowing of the palpebral fissure. Most individuals with Duane syndrome have strabismus in primary gaze but can use a compensatory head position to align the eyes, and thus can preserve single binocular vision and avoid diplopia. Individuals with Duane syndrome who lack binocular vision are at risk for amblyopia. Approximately 70% of individuals with Duane syndrome have isolated Duane syndrome (i.e., they do not have other detected congenital anomalies). [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1190]
Werner syndrome is characterized by the premature appearance of features associated with normal aging and cancer predisposition. Individuals with Werner syndrome develop normally until the end of the first decade. The first sign is the lack of a growth spurt during the early teen years. Early findings (usually observed in the 20s) include loss and graying of hair, hoarseness, and scleroderma-like skin changes, followed by bilateral ocular cataracts, type 2 diabetes mellitus, hypogonadism, skin ulcers, and osteoporosis in the 30s. Myocardial infarction and cancer are the most common causes of death; the mean age of death in individuals with Werner syndrome is 54 years. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1514]
Homocystinuria Caused by Cystathionine Beta-Synthase Deficiency
Homocystinuria caused by cystathionine β-synthase (CBS) deficiency is characterized by developmental delay/intellectual disability, ectopia lentis and/or severe myopia, skeletal abnormalities (excessive height and length of the limbs), and thromboembolism. Expressivity is variable for all of the clinical signs. Two phenotypic variants are recognized, B6-responsive homocystinuria and B6-non-responsive homocystinuria. B6-responsive homocystinuria is typically, but not always, milder than the non-responsive variant. In the majority of untreated affected individuals, ectopia lentis occurs by age eight years. Individuals are often tall and slender with an asthenic (‘marfanoid’) habitus and are prone to osteoporosis. Thromboembolism is the major cause of early death and morbidity. IQ in individuals with untreated homocystinuria ranges widely, from 10 to 138. In B6-responsive individuals the mean IQ is 79 versus 57 for those who are B6 non-responsive. Other features that may occur include: seizures, psychiatric problems, extrapyramidal signs (e.g., dystonia), hypopigmentation, malar flush, livedo reticularis, and pancreatitis. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1524]
Alexander disease is a progressive disorder of cerebral white matter that predominantly affects infants and children and has variable life expectancy. The later-onset forms present with a slower clinical course. The infantile form comprises about 42% of affected individuals, the juvenile form about 22%, and the adult form about 33%. A neonatal form is also recognized.The neonatal form leads to severe disability or death within two years. Characteristics include seizures, hydrocephalus, severe motor and intellectual disability, and elevated CSF protein concentration. MRI shows severe white matter abnormalities with involvement of the basal ganglia and cerebellum. The infantile form presents in the first two years of life, typically with progressive psychomotor retardation with loss of developmental milestones, megalencephaly, frontal bossing, and seizures. Other findings include hyperreflexia and pyramidal signs, ataxia, and occasional hydrocephalus secondary to aqueductal stenosis. Affected children survive weeks to several years. The juvenile form usually presents between ages four and ten years, occasionally in the mid-teens. Findings can include bulbar/pseudobulbar signs, ataxia, gradual loss of intellectual function, seizures, normocephaly or megalencephaly, and breathing problems. Survival ranges from the early teens to the 20s-30s. The adult form is the most variable. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1172]
Deafness-Dystonia-Optic Neuronopathy Syndrome
Males with deafness-dystonia-optic neuronopathy (DDON) syndrome have prelingual or postlingual sensorineural hearing impairment in early childhood, slowly progressive dystonia or ataxia in the teens, slowly progressive decreased visual acuity from optic atrophy beginning approximately age 20 years, and dementia beginning at approximately age 40 years. Psychiatric symptoms such as personality change and paranoia may appear in childhood and progress. The hearing impairment appears to be consistent in age of onset and progression, whereas the neurologic, visual, and neuropsychiatric signs vary in degree of severity and rate of progression. Females may have mild hearing impairment and focal dystonia. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1216]
SOST-related sclerosing bone dysplasias include sclerosteosis and van Buchem disease; both are disorders of osteoblast hyperactivity. The major clinical features of sclerosteosis are progressive skeletal overgrowth and variable syndactyly, usually of the second (index) and third (middle) fingers. Affected individuals appear normal at birth except for syndactyly. Distinctive facial features including asymmetric mandibular hypertrophy, frontal bossing, and midface hypoplasia are usually apparent by mid-childhood. Hyperostosis of the skull results in narrowing of the foramina, causing entrapment of the seventh cranial nerve (often leading to facial palsy) and entrapment of the eighth cranial nerve (often resulting in deafness in mid-childhood). In sclerosteosis, hyperostosis of the calvarium reduces intracranial volume, increasing the risk for potentially lethal elevation of intracranial pressure. Survival of individuals with sclerosteosis into old age is unusual. The manifestations of van Buchem disease are generally milder than sclerosteosis and syndactyly is absent. Based on a few case reports, it is also likely that the spectrum of SOST-related sclerosing bone dysplasias includes an autosomal dominant form of craniodiaphyseal dysplasia (CDD). [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1228]
Nonsyndromic 46,XX Testicular Disorders of Sex Development
Nonsyndromic 46,XX testicular disorders of sex development (46,XX testicular DSD) are characterized by the presence of a 46,XX karyotype; male external genitalia ranging from normal to ambiguous; two testicles; azoospermia; and absence of Müllerian structures. Approximately 85% of individuals with nonsyndromic 46,XX testicular DSD present after puberty with normal pubic hair and normal penile size, but small testes, gynecomastia, and sterility resulting from azoospermia. Approximately 15% of individuals with nonsyndromic 46,XX testicular DSD present at birth with ambiguous genitalia. Gender role and gender identity are reported as male. If untreated, males with 46,XX testicular DSD experience the consequences of testosterone deficiency. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1416]
Untreated tyrosinemia type I usually presents either in young infants with severe liver involvement or later in the first year with liver dysfunction and renal tubular dysfunction associated with growth failure and rickets. Untreated children may have repeated, often unrecognized, neurologic crises lasting one to seven days that can include change in mental status, abdominal pain, peripheral neuropathy, and/or respiratory failure requiring mechanical ventilation. Death in the untreated child usually occurs before age ten years, typically from liver failure, neurologic crisis, or hepatocellular carcinoma. Combined treatment with nitisinone and a low-tyrosine diet has resulted in a greater than 90% survival rate, normal growth, improved liver function, prevention of cirrhosis, correction of renal tubular acidosis, and improvement in secondary rickets. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1515]
Congenital Insensitivity to Pain with Anhidrosis
Congenital insensitivity to pain with anhidrosis (CIPA), also known as hereditary sensory and autonomic neuropathy type IV (HSAN IV), is characterized by insensitivity to pain, anhidrosis (the inability to sweat), and intellectual disability. The ability to sense all pain (including visceral pain) is absent, resulting in repeated injuries including: oral self-mutilation (biting of tongue, lips, and buccal mucosa); biting of fingertips; bruising, scarring, and infection of the skin; multiple bone fractures (many of which fail to heal properly); and recurrent joint dislocations resulting in joint deformity. Sense of touch, vibration, and position are normal. Anhidrosis predisposes to recurrent febrile episodes that are often the initial manifestation of CIPA. Hypothermia in cold environments also occurs. Intellectual disability of varying degree is observed in most affected individuals; hyperactivity and emotional lability are common. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1769]
The clinical manifestations of LAMA2-related muscular dystrophy (LAMA2 MD) range from severe, early-onset congenital muscular dystrophy (CMD) – referred to as early-onset LAMA2-related muscular dystrophy (LAMA2 MD) in this GeneReview – to mild, later childhood-onset limb-girdle type muscular dystrophy – referred to here as late-onset LAMA2-related muscular dystrophy (LAMA2 MD). Children with early-onset LAMA2 MD have profound hypotonia with muscle weakness evident at birth or within the first six months of life, poor spontaneous movements with contractures of the large joints, and weak cry often associated with respiratory failure. Feeding difficulties with failure to thrive, aspiration, and recurrent chest infections are typical. Progressive scoliosis starting in childhood is common. Seizures and, less often, cardiac involvement can occur. Typically, individuals with early-onset LAMA2 MD do not achieve independent ambulation. Intellect is usually normal. Those with limb-girdle type muscular dystrophy have later onset of proximal muscle weakness and delayed motor milestones, but achieve independent ambulation; they may develop a rigid spine syndrome with joint contractures. Progressive respiratory insufficiency and scoliosis can occur. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK97333]
SCA10 is characterized by slowly progressive cerebellar ataxia that usually starts as poor balance and unsteady gait, followed by upper-limb ataxia, scanning dysarthria, and dysphagia. The disease is exclusively found in Latin American populations, particularly those with Amerindian admixture. Abnormal tracking eye movements are common. Recurrent seizures after the onset of gait ataxia have been reported with variable frequencies among different families. Some individuals have cognitive dysfunction, behavioral disturbances, mood disorders, mild pyramidal signs, and peripheral neuropathy. Onset ranges from age 12 to 48 years. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1175]
Acute intermittent porphyria (referred to as AIP in this GeneReview) results from half-normal activity of the enzyme hydroxymethylbilane synthase (HMBS). It is characterized clinically by life-threatening acute neurovisceral attacks of severe abdominal pain without peritoneal signs, often accompanied by nausea, vomiting, tachycardia, and hypertension. Attacks may be complicated by neurologic findings (mental changes, convulsions, and peripheral neuropathy that may progress to respiratory paralysis), and hyponatremia. Acute attacks, which may be provoked by certain drugs, alcoholic beverages, endocrine factors, calorie restriction, stress, and infections, usually resolve within two weeks. Most individuals with AIP have one or a few attacks; about 5% (mainly women) have recurrent attacks (defined as >4 attacks/year) that may persist for years. Other long-term complications are chronic renal failure, hepatocellular carcinoma (HCC), and hypertension. Attacks, which are very rare before puberty, are more common in women than men. All individuals with a genetic change in the gene HMBS that predisposes to AIP are at risk of developing acute attacks; however, most never have symptoms and are said to have latent (or presymptomatic) AIP. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1193]
Rothmund-Thomson syndrome (RTS) is characterized by poikiloderma; sparse hair, eyelashes, and/or eyebrows; small stature; skeletal and dental abnormalities; cataracts; and an increased risk for cancer, especially osteosarcoma. The skin is typically normal at birth; the rash of RTS develops between age three and six months as erythema, swelling, and blistering on the face and subsequently spreads to the buttocks and extremities. The rash evolves over months to years into the chronic pattern of reticulated hypo- and hyperpigmentation, punctate atrophy, and telangiectases, collectively known as poikiloderma. Hyperkeratotic lesions occur in approximately one third of individuals. Skeletal abnormalities include dysplasias, absent or malformed bones (such as absent radii), osteopenia, and delayed bone formation. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1237]
Andersen-Tawil syndrome (ATS) is characterized by a triad of episodic flaccid muscle weakness (i.e., periodic paralysis), ventricular arrhythmias and prolonged QT interval, and anomalies including low-set ears, widely spaced eyes, small mandible, fifth-digit clinodactyly, syndactyly, short stature, and scoliosis. Affected individuals present in the first or second decade with either cardiac symptoms (palpitations and/or syncope) or weakness that occurs spontaneously following prolonged rest or following rest after exertion. Mild permanent weakness is common. Mild learning difficulties and a distinct neurocognitive phenotype (i.e., deficits in executive function and abstract reasoning) have been described. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1264]
Spinal and bulbar muscular atrophy (SBMA) is a gradually progressive neuromuscular disorder in which degeneration of lower motor neurons results in muscle weakness, muscle atrophy, and fasciculations. SBMA occurs only in males. Affected individuals often show gynecomastia, testicular atrophy, and reduced fertility as a result of mild androgen insensitivity. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1333]
Type II porphyria cutanea tarda (type II PCT) is characterized by: Blistering over the dorsal aspects of the hands and other sun-exposed areas of skin, skin friability after minor trauma, facial hypertrichosis and hyperpigmentation, and severe thickening of affected skin areas (pseudoscleroderma); and An increased risk for hepatocellular carcinoma (HCC). [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK143129]
Episodic ataxia type 1 (EA1) is a potassium channelopathy characterized by constant myokymia and dramatic episodes of spastic contractions of the skeletal muscles of the head, arms, and legs with loss of both motor coordination and balance. During attacks individuals may experience a number of variable symptoms including vertigo, blurred vision, diplopia, nausea, headache, diaphoresis, clumsiness, stiffening of the body, dysarthric speech, and difficulty in breathing, among others. EA1 may be associated with epilepsy. Other findings can include delayed motor development, cognitive disability, choreoathetosis, and carpal spasm. Usually, onset is in childhood or early adolescence. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK25442]
Phosphorylase kinase (PhK) deficiency causing glycogen storage disease type IX (GSD IX) results from deficiency of the enzyme phosphorylase b kinase, which has a major regulatory role in the breakdown of glycogen. The two types of PhK deficiency are liver PhK deficiency (characterized by early childhood onset of hepatomegaly and growth retardation, and often, but not always, fasting ketosis and hypoglycemia) and muscle PhK deficiency, which is considerably rarer (characterized by any of the following: exercise intolerance, myalgia, muscle cramps, myoglobinuria, and progressive muscle weakness). Symptoms and biochemical abnormalities of liver PhK deficiency are thought to improve with age. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK55061]
TARDBP-Related Amyotrophic Lateral Sclerosis
TARDBP-related amyotrophic lateral sclerosis (TARDBP-related ALS) is characterized by upper motor neuron (UMN) and lower motor neuron (LMN) disease that appears indistinguishable from ALS of other known and unknown causes based on gender ratio, age of onset, symptom distribution, and severity of disease. The male to female ratio is 1.6 to 1. Mean age of onset is 54 ± 12 years. UMN manifestations can include stiffness, spasticity, hyperreflexia, and pseudobulbar affect; LMN manifestations often include weakness accompanied by muscle atrophy, fasciculations, and cramping. Limb onset occurs in 80% and bulbar onset in 20%. Affected individuals typically succumb to respiratory failure when phrenic and thoracic motor neurons become severely involved. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK5942]
The spectrum of CLCN7-related osteopetrosis includes infantile malignant CLCN7-related recessive osteopetrosis (ARO), intermediate autosomal osteopetrosis (IAO), and autosomal dominant osteopetrosis type II (ADOII, Albers-Schoenberg disease).Onset of ARO is in infancy; findings may include fractures; poor growth; sclerosis of the skull base (with or without choanal stenosis or hydrocephalus) resulting in optic nerve compression, facial palsy, and hearing loss; absence of the bone marrow cavity resulting in severe anemia and thrombocytopenia; dental abnormalities, odontomas, and risk for mandibular osteomyelitis; and hypocalcemia with tetanic seizures and secondary hyperparathyroidism. Without treatment maximal life span in ARO is ten years. Onset of IAO is in childhood; findings may include fractures after minor trauma, characteristic skeletal radiographic changes found incidentally, mild anemia, and occasional visual impairment secondary to optic nerve compression. Life expectancy in IAO is usually normal. Onset of ADOII is usually late childhood or adolescence; findings may include fractures (in any long bone and/or the posterior arch of a vertebra); scoliosis; hip osteoarthritis; osteomyelitis of the mandible or septic osteitis or osteoarthritis elsewhere. Cranial nerve compression is rare. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1127]
Jervell and Lange-Nielsen syndrome (JLNS) is characterized by congenital profound bilateral sensorineural hearing loss and long QTc, usually greater than 500 msec. Prolongation of the QTc interval is associated with tachyarrhythmias, including ventricular tachycardia, episodes of torsade de pointes ventricular tachycardia, and ventricular fibrillation, which may culminate in syncope or sudden death. Iron-deficient anemia and elevated levels of gastrin are also frequent features of JLNS. The classic presentation of JLNS is a deaf child who experiences syncopal episodes during periods of stress, exercise, or fright. Fifty percent of individuals with JLNS had cardiac events before age three years. More than half of untreated children with JLNS die prior to age 15 years. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1405]
Primary familial brain calcification (PFBC) is a neurodegenerative disorder with characteristic calcium deposits in the basal ganglia and other brain areas visualized on neuroimaging. Most affected individuals are in good health during childhood and young adulthood and typically present in the fourth to fifth decade with gradually progressive neuropsychiatric and movement disorders. The main manifestations include clumsiness, fatigability, unsteady gait, slow or slurred speech, dysphagia, involuntary movements, or muscle cramping. Migraine is frequent and seizures of various types may also occur. Neuropsychiatric symptoms, often the first or most prominent manifestations, range from mild difficulty with concentration and memory to changes in personality and/or behavior, to psychosis and dementia. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1421]
McKusick-Kaufman syndrome (MKS) is characterized by the combination of postaxial polydactyly (PAP), congenital heart disease (CHD), and hydrometrocolpos (HMC) in females and genital malformations in males (most commonly hypospadias, cryptorchidism, and chordee). HMC in infants usually presents as a large cystic abdominal mass arising out of the pelvis, caused by dilatation of the vagina and uterus as a result of the accumulation of cervical secretions from maternal estrogen stimulation. HMC can be caused by failure of the distal third of the vagina to develop (vaginal agenesis), a transverse vaginal membrane, or an imperforate hymen. Cardiac malformations that have been described at least once in individuals with MKS include atrioventricularis (AV) communis with a left-sided superior vena cava, atrial septal defect, ventricular septal defect, AV canal, small aorta and hypoplastic left ventricle, tetralogy of Fallot, and patent ductus arteriosus. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1502]
Celiac disease is a systemic autoimmune disease that can be associated with gastrointestinal findings (diarrhea, weight loss, abdominal pain, anorexia, lactose intolerance, abdominal distention, and irritability) and/or highly variable non-gastrointestinal findings (iron deficiency anemia, dermatitis herpetiformis, chronic fatigue, joint pain/inflammation, migraines, depression, attention-deficit disorder, epilepsy, osteoporosis/osteopenia, infertility and/or recurrent fetal loss, vitamin deficiencies, short stature, failure to thrive, delayed puberty, dental enamel defects, and autoimmune disorders). Classic celiac disease, characterized by mild to severe gastrointestinal symptoms, is less common than non-classic celiac disease, characterized by absence of gastrointestinal symptoms. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1727]
DICER1-related disorders are a familial tumor susceptibility syndrome that confers increased risk most commonly for pleuropulmonary blastoma (PPB); ovarian sex cord-stromal tumors (Sertoli-Leydig cell tumor [SLCT], juvenile granulosa cell tumor [JGCT], and gynandroblastoma); cystic nephroma (CN); and thyroid gland neoplasia (multinodular goiter [MNG], adenomas, or differentiated thyroid cancer). Less commonly observed tumors are ciliary body medulloepithelioma (CBME); botryoid-type embryonal rhabdomyosarcoma (ERMS) of the cervix or other sites; nasal chondromesenchymal hamartoma (NCMH); renal sarcoma; pituitary blastoma; and pineoblastoma. Novel phenotypes continue to be discovered. The majority of tumors in families with a DICER1 germline pathogenic variant occur in individuals younger than age 40 years. PPB, a neoplasm that arises during lung development or shortly after birth, typically presents in infants and children younger than age six years. Age of onset of ovarian sex cord-stromal tumors is not well defined. CN presents in children younger than age four years. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK196157]
The phenotypic spectrum of X-linked hypophosphatemia (XLH) ranges from isolated hypophosphatemia to severe lower-extremity bowing. XLH frequently manifests in the first two years of life when lower-extremity bowing becomes evident with the onset of weight bearing; however, it sometimes is not manifest until adulthood, as previously unevaluated short stature. Additionally, in adults enthesopathy (calcification of the tendons, ligaments, and joint capsules) may be the initial presenting complaint. Persons with XLH are prone to spontaneous dental abscesses; sensorineural hearing loss has also been reported. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK83985]
Spondylocostal Dysostosis, Autosomal Recessive
Spondylocostal dysostosis (SCDO), defined radiographically as multiple segmentation defects of the vertebrae (M-SDV) in combination with abnormalities of the ribs, is characterized clinically by: a short trunk in proportion to height; short neck; and non-progressive mild scoliosis in most affected individuals, and occasionally, more significant scoliosis. Respiratory function in neonates may be compromised by reduced size of the thorax. By age two years lung growth may improve sufficiently to support relatively normal growth and development; however, even then life-threatening complications can occur, especially pulmonary hypertension in children with severely restricted lung capacity from birth. Males with SCDO appear to be at increased risk for inguinal hernia. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK8828]
Ataxia with oculomotor apraxia type 2 (AOA2) is characterized by onset between age three and 30 years, cerebellar atrophy, axonal sensorimotor neuropathy, oculomotor apraxia, and elevated serum concentration of alpha-fetoprotein (AFP). [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1154]
Hereditary Nephrogenic Diabetes Insipidus
Nephrogenic diabetes insipidus (NDI) is characterized by inability to concentrate the urine, which results in polyuria (excessive urine production) and polydipsia (excessive thirst). Affected untreated infants usually have poor feeding and failure to thrive, and rapid onset of severe dehydration with illness, hot environment, or the withholding of water. Short stature and secondary dilatation of the ureters and bladder from the high urine volume is common in untreated individuals. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1177]
SCA8 is a slowly progressive ataxia with disease onset typically occurring in adulthood. Onset ranges from age one to 73 years. The progression is typically over decades regardless of the age of onset. Common initial symptoms are scanning dysarthria with a characteristic drawn-out slowness of speech and gait instability; life span is typically not shortened. Some individuals present with nystagmus, dysmetric saccades and, rarely, ophthalmoplegia. Tendon reflex hyperreflexity and extensor plantar responses are present in some severely affected individuals. Life span is typically not shortened. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1268]
Glucose Transporter Type 1 Deficiency Syndrome
The phenotypic spectrum of glucose transporter type 1 deficiency syndrome (Glut1-DS) is now known to be a continuum that includes the classic phenotype as well as dystonia 9, dystonia 18, atypical childhood absence epilepsy, myoclonic astatic epilepsy, and paroxysmal non-epileptic findings such as intermittent ataxia, choreoathetosis, dystonia, and alternating hemiplegia. The classic phenotype is characterized by infantile-onset seizures, delayed neurologic development, acquired microcephaly, and complex movement disorders. Seizures begin before age two years in approximately 90% and later in approximately 10%. Several seizure types occur: generalized tonic or clonic, focal, myoclonic, atypical absence, atonic, and unclassified. The frequency, severity, and type of seizures vary among affected individuals and are not related to disease severity. Cognitive impairment, ranging from learning disabilities to severe intellectual disability, is typical. The complex movement disorder, characterized by ataxia, dystonia, and chorea, may occur in any combination and may be continuous, paroxysmal, or continuous with fluctuations in severity influenced by environmental factors such as fasting, fever, and intercurrent infection. Symptoms often improve substantially when a ketogenic diet is started. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1430]
Blepharophimosis, Ptosis, and Epicanthus Inversus
Blephariphimosis, ptosis, and epicanthus inversus syndrome (BPES) is a complex eyelid malformation invariably characterized by four major features: blepharophimosis, ptosis, epicanthus inversus, and telecanthus. BPES type I includes the four major features and premature ovarian insufficiency (POI); BPES type II includes only the four major features. Other ophthalmic manifestations that can be associated with BPES include lacrimal duct anomalies, amblyopia, strabismus, and refractive errors. Minor features include a broad nasal bridge, low-set ears, and a short philtrum. Individuals with BPES and an intragenic FOXL2 pathogenic variant are expected to have normal intelligence, in contrast to affected individuals with cytogenetic rearrangements that involve FOXL2 and additional genes. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1441]
The WAS-related disorders, which include Wiskott-Aldrich syndrome, X-linked thrombocytopenia (XLT), and X-linked congenital neutropenia (XLN), are a spectrum of disorders of hematopoietic cells, with predominant defects of platelets and lymphocytes caused by pathogenic variants in WAS. WAS-related disorders usually present in infancy. Affected males have thrombocytopenia with intermittent mucosal bleeding, bloody diarrhea, and intermittent or chronic petechiae and purpura; eczema; and recurrent bacterial and viral infections, particularly recurrent ear infections. At least 40% of those who survive the early complications develop one or more autoimmune conditions including hemolytic anemia, immune thrombocytopenic purpura (ITP), immune-mediated neutropenia, arthritis, vasculitis of small and large vessels, and immune-mediated damage to the kidneys and liver. Individuals with a WAS-related disorder, particularly those who have been exposed to Epstein-Barr virus (EBV), have an increased risk of developing lymphomas, which often occur in unusual, extranodal locations such as the brain, lung, or gastrointestinal tract. Males with XLT have thrombocytopenia with small platelets; other complications of Wiskott-Aldrich syndrome, including eczema and immune dysfunction, are mild or absent. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1178]
Alport syndrome (AS) is characterized by renal, cochlear, and ocular involvement. Renal disease progresses from microscopic hematuria to proteinuria, progressive renal insufficiency, and end-stage renal disease (ESRD) in all males with X-linked (XL) AS, and in all males and females with autosomal recessive (AR) AS. Progressive sensorineural hearing loss (SNHL) is usually present by late childhood or early adolescence. Ocular findings include anterior lenticonus (which is virtually pathognomonic), maculopathy (whitish or yellowish flecks or granulations in the perimacular region), corneal endothelial vesicles (posterior polymorphous dystrophy), and recurrent corneal erosion. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1207]
Mitochondrial diseases are a clinically heterogeneous group of disorders that arise as a result of dysfunction of the mitochondrial respiratory chain. They can be caused by mutation of genes encoded by either nuclear DNA or mitochondrial DNA (mtDNA). While some mitochondrial disorders only affect a single organ (e.g., the eye in Leber hereditary optic neuropathy [LHON]), many involve multiple organ systems and often present with prominent neurologic and myopathic features. Mitochondrial disorders may present at any age. Many individuals with a mutation of mtDNA display a cluster of clinical features that fall into a discrete clinical syndrome, such as the Kearns-Sayre syndrome (KSS), chronic progressive external ophthalmoplegia (CPEO), mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS), myoclonic epilepsy with ragged-red fibers (MERRF), neurogenic weakness with ataxia and retinitis pigmentosa (NARP), or Leigh syndrome (LS). However, considerable clinical variability exists and many individuals do not fit neatly into one particular category, which is well-illustrated by the overlapping spectrum of disease phenotypes (including mitochondrial recessive ataxia syndrome (MIRAS) resulting from mutation of the nuclear gene POLG, which has emerged as a major cause of mitochondrial disease. Common clinical features of mitochondrial disease – whether involving a mitochondrial or nuclear gene – include ptosis, external ophthalmoplegia, proximal myopathy and exercise intolerance, cardiomyopathy, sensorineural deafness, optic atrophy, pigmentary retinopathy, and diabetes mellitus. Common central nervous system findings are fluctuating encephalopathy, seizures, dementia, migraine, stroke-like episodes, ataxia, and spasticity. A high incidence of mid- and late pregnancy loss is a common occurrence that often goes unrecognized. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1224]
Catecholaminergic Polymorphic Ventricular Tachycardia
Catecholaminergic polymorphic ventricular tachycardia (CPVT) is characterized by episodic syncope occurring during exercise or acute emotion in individuals without structural cardiac abnormalities. Arrhythmias may be well tolerated, with only mild symptoms such as dizziness or lypothymia. The underlying cause of these episodes is the onset of fast ventricular tachycardia (bidirectional or polymorphic). Spontaneous recovery occurs when these arrhythmias self-terminate. In other instances, ventricular tachycardia may degenerate into ventricular fibrillation and cause sudden death if cardiopulmonary resuscitation is not readily available. The mean age of onset of symptoms (usually a syncopal episode) of CPVT is between age seven and twelve years; onset as late as the fourth decade of life has been reported. If untreated, CPVT is highly lethal, as approximately 30% of affected individuals experience at least one cardiac arrest and up to 80% one or more syncopal spells. Sudden death may be the first manifestation of the disease. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1289]
Mowat-Wilson syndrome (MWS) is characterized by the following:Distinctive facial features Structural anomalies including: Hirschsprung diseaseGenitourinary anomalies (particularly hypospadias in males)Congenital heart defects (particularly abnormalities of the pulmonary arteries and/or valves)Agenesis or hypogenesis of the corpus callosumEye defects (microphthalmia and Axenfeld anomaly) Hirschsprung disease Genitourinary anomalies (particularly hypospadias in males) Congenital heart defects (particularly abnormalities of the pulmonary arteries and/or valves) Agenesis or hypogenesis of the corpus callosum Eye defects (microphthalmia and Axenfeld anomaly) Functional differences including:Moderate to severe intellectual disabilitySevere speech impairment with relative preservation of receptive languageSeizuresGrowth retardation with microcephalyChronic constipation in those without Hirschsprung disease Moderate to severe intellectual disability Severe speech impairment with relative preservation of receptive language Seizures Growth retardation with microcephaly Chronic constipation in those without Hirschsprung disease [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1412]
Incontinentia pigmenti (IP) is a disorder that affects the skin, hair, teeth, nails, eyes, and central nervous system. Characteristic skin lesions evolve through four stages: [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1472]
Treacher Collins syndrome (TCS) is characterized by hypoplasia of the zygomatic bones and mandible, external ear abnormalities, coloboma (notching) of the lower eyelid, absence of the lower eyelashes, and preauricular hair displacement onto the cheeks. About 40%-50% of individuals have conductive hearing loss attributed most commonly to malformation (including ankylosis, hypoplasia, or absence) of the ossicles and hypoplasia of the middle ear cavities. Inner ear structures tend to be normal. Other less common abnormalities include cleft palate with or without cleft lip and unilateral or bilateral choanal stenosis or atresia. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1532]
Most individuals with ataxia with vitamin E deficiency (AVED) present at puberty; common characteristics of the disease include progressive ataxia, clumsiness of the hands, loss of proprioception (especially of vibration and joint position sense), and areflexia. Other features often observed are dysdiadochokinesia, positive Romberg sign, head titubation, decreased visual acuity, and positive Babinski sign. The phenotype and disease severity vary widely among families with different mutations; age of onset and disease course are more uniform within a given family, but symptoms and disease severity can vary even among sibs. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1241]
Carnitine Palmitoyltransferase II Deficiency
Carnitine palmitoyltransferase II (CPT II) deficiency is a disorder of long-chain fatty-acid oxidation. The three clinical presentations are: lethal neonatal form, severe infantile hepatocardiomuscular form, and myopathic form (which is usually mild and can manifest from infancy to adulthood). While the former two are severe multisystemic diseases characterized by liver failure with hypoketotic hypoglycemia, cardiomyopathy, seizures, and early death, the latter is characterized by exercise-induced muscle pain and weakness, sometimes associated with myoglobinuria. The myopathic form of CPT II deficiency is the most common disorder of lipid metabolism affecting skeletal muscle and is the most frequent cause of hereditary myoglobinuria. Males are more likely to be affected than females. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1253]
Glycine encephalopathy, also known as nonketotic hyperglycinemia (NKH), is an inborn error of glycine metabolism defined by deficient activity of the glycine cleavage enzyme and, as a consequence, accumulation of large quantities of glycine in all body tissues including the brain. The majority of glycine encephalopathy presents in the neonatal period (85% as the neonatal severe form and 15% as the neonatal attenuated form). Of those presenting in infancy, 50% have the infantile attenuated form and 50% have the infantile severe form. Overall, 20% of all children presenting as either neonates or infants have a less severe outcome, defined as developmental quotient greater than 20. A minority of patients have mild or atypical forms of glycine encephalopathy. The neonatal form manifests in the first hours to days of life with progressive lethargy, hypotonia, and myoclonic jerks leading to apnea and often death. Surviving infants have profound intellectual disability and intractable seizures. The infantile form is characterized by hypotonia, developmental delay, and seizures. The atypical forms range from milder disease, with onset from late infancy to adulthood, to rapidly progressing and severe disease with late onset. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1357]
Epidermolysis bullosa simplex (EBS) is characterized by fragility of the skin (and mucosal epithelia in some cases) that results in nonscarring blisters caused by little or no trauma. The current classification of epidermolysis bullosa (EB) includes two major types and 12 minor subtypes of EBS; all share the common feature of blistering above the dermal-epidermal junction at the ultrastructural level. The four most common subtypes of EBS are the focus of this GeneReview:EBS, localized (EBS-loc; previously known as Weber-Cockayne type) EBS, Dowling-Meara type (EBS-DM) EBS, other generalized (EBS, gen-nonDM; previously known as Koebner type) EBS-with mottled pigmentation (EBS-MP) [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1369]
The clinical characteristics of Birt-Hogg-Dubé syndrome (BHDS) include cutaneous manifestations (fibrofolliculomas, trichodiscomas/angiofibromas, perifollicular fibromas, and acrochordons), pulmonary cysts/history of pneumothorax, and various types of renal tumors. Disease severity can vary significantly even within the same family. Skin lesions typically appear during the third and fourth decades of life and typically increase in size and number with age. Lung cysts are mostly bilateral and multifocal; most individuals are asymptomatic but at high risk for spontaneous pneumothorax. Individuals with BHDS are at a sevenfold increased risk for renal tumors that are typically bilateral and multifocal and usually slow growing; median age of tumor diagnosis is 48 years. The most common renal tumors are a hybrid of oncocytoma and chromophobe histologic cell types (so-called oncocytic hybrid tumor) and chromophobe histologic cell types. Some families have renal tumor and/or autosomal dominant spontaneous pneumothorax without cutaneous manifestations. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1522]
X-linked chondrodysplasia punctata 1 (CDPX1), a congenital disorder of bone and cartilage development, is caused by a deficiency of the Golgi enzyme arylsulfatase E (ARSE). It is characterized by chondrodysplasia punctata (stippled epiphyses), brachytelephalangy (shortening of the distal phalanges), and nasomaxillary hypoplasia. Although most affected males have minimal morbidity and skeletal findings that improve by adulthood, some have significant medical problems including respiratory compromise, cervical spine stenosis and instability, mixed conductive and sensorineural hearing loss, and intellectual disability. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1544]
NKX2-1-related disorders range from benign hereditary chorea (BHC) to choreoathetosis, congenital hypothyroidism, and neonatal respiratory distress (also known as brain-lung-thyroid syndrome). Childhood-onset chorea, the hallmark of NKX2-1-related disorders, may or may not be associated with respiratory distress syndrome or congenital hypothyroidism. Chorea generally begins in early infancy or about age one year (most commonly) or in late childhood or adolescence, and progresses into the second decade after which it remains static or (rarely) remits. Pulmonary disease, the second most common manifestation, can include respiratory distress syndrome in neonates, interstitial lung disease in young children, and pulmonary fibrosis in older persons. The risk for pulmonary carcinoma is increased in young adults with an NKX2-1-related disorder. Thyroid dysfunction, the result of dysembryogenesis, can present as congenital hypothyroidism or compensated hypothyroidism. The risk for thyroid cancer is unknown and may not be increased. In one review, 50% of affected individuals had the full brain-lung-thyroid syndrome, 30% had involvement of brain and thyroid only, and 13% had isolated chorea only. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK185066]
Congenital hepatic fibrosis (CHF) is a developmental disorder of the portobiliary system characterized histologically by defective remodeling of the ductal plate (ductal plate malformation; DPM), abnormal branching of the intrahepatic portal veins, and progressive fibrosis of the portal tracts. CHF may or may not be associated with macroscopic cystic dilatation of the intrahepatic bile ducts. Clinical findings include enlarged, abnormally shaped liver, relatively well-preserved hepatocellular function, and portal hypertension (PH) resulting in splenomegaly, hypersplenism, and gastroesophageal varices. Pulmonary hypertension (portopulmonary hypertension) and vascular shunts in the pulmonary parenchyma (hepatopulmonary syndrome), complications of PH, can also be seen rarely. Most frequently CHF is associated with ciliopathies (disorders of the primary cilia) that have associated renal disease, the so-called hepatorenal fibrocystic diseases (FCDs). Although the hepatorenal FCDs are currently classified by phenotype, it is likely that gene-based classification will be quite different in the future because of the tremendous genetic and phenotypic overlap between these disorders. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK2701]
Long QT syndrome (LQTS) is a cardiac electrophysiologic disorder, characterized by QT prolongation and T-wave abnormalities on the ECG and the ventricular tachycardia torsade de pointes (TdP). TdP is usually self-terminating, thus causing a syncopal event, the most common symptom in individuals with LQTS. Syncope typically occurs during exercise and high emotions, less frequently at rest or during sleep, and usually without warning. In some instances, TdP degenerates to ventricular fibrillation and causes aborted cardiac arrest (if the individual is defibrillated) or sudden death. Approximately 50% of individuals with a pathogenic variant in one of the genes associated with LQTS have symptoms, usually one to a few syncopal spells. While cardiac events may occur from infancy through middle age, they are most common from the pre-teen years through the 20s. Some types of LQTS are associated with a phenotype extending beyond cardiac arrhythmia. In addition to the prolonged QT interval, associations include muscle weakness and facial dysmorphism in Andersen-Tawil syndrome (LQTS type 7), hand/foot, facial, and neurodevelopmental features in Timothy syndrome (LQTS type 8) and profound sensorineural hearing loss in Jervell and Lange-Nielson syndrome. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1129]
Loeys-Dietz syndrome (LDS) is characterized by vascular findings (cerebral, thoracic, and abdominal arterial aneurysms and/or dissections) and skeletal manifestations (pectus excavatum or pectus carinatum, scoliosis, joint laxity, arachnodactyly, talipes equinovarus). Approximately 75% of affected individuals have LDS type I with craniofacial manifestations (widely spaced eyes, bifid uvula/cleft palate, craniosynostosis); approximately 25% have LDS type II with systemic manifestations of LDSI but minimal or absent craniofacial features. LDSI and LDSII form a clinical continuum. The natural history of LDS is characterized by aggressive arterial aneurysms (mean age at death 26.1 years) and a high incidence of pregnancy-related complications, including death and uterine rupture. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1133]
Baller-Gerold syndrome (BGS) is characterized by coronal craniosynostosis, manifest as abnormal shape of the skull (brachycephaly) with ocular proptosis and bulging forehead; radial ray defect, manifest as oligodactyly (reduction in number of digits), aplasia or hypoplasia of the thumb, and/or aplasia or hypoplasia of the radius; growth retardation and poikiloderma. Findings in individuals with BGS overlap with those of Rothmund-Thomson syndrome (RTS) and RAPADILINO syndrome, also caused by mutations in RECQL4. RTS is characterized by poikiloderma; sparse hair, eyelashes, and/or eyebrows/lashes; small stature; skeletal and dental abnormalities; cataracts; and an increased risk for cancer, especially osteosarcoma. RAPADILINO syndrome is an acronym for RAdial ray defect; PAtellae hypoplasia or aplasia and cleft or highly arched PAlate; DIarrhea and DIslocated joints; LIttle size and LImb malformation; NOse slender and NOrmal intelligence. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1204]
Smith-Magenis syndrome (SMS) is characterized by distinctive physical features (particularly facial features that progress with age), developmental delay, cognitive impairment, and behavioral abnormalities. Infants have feeding difficulties, failure to thrive, hypotonia, hyporeflexia, prolonged napping or need to be awakened for feeds, and generalized lethargy. The majority of individuals function in the mild-to-moderate range of intellectual disability. The behavioral phenotype, including significant sleep disturbance, stereotypies, and maladaptive and self-injurious behaviors, is generally not recognized until age 18 months or older and continues to change until adulthood. Sensory integration issues are frequently noted. Children and adults typically have inattention, distractibility, hyperactivity, impulsivity, maladaptive behaviors including frequent outbursts/temper tantrums, attention seeking, disobedience, aggression, toileting difficulties, and self-injurious behaviors (SIB) including self-hitting, self-biting, and/or skin picking, inserting foreign objects into body orifices (polyembolokoilamania), and yanking fingernails and/or toenails (onychotillomania). Among the stereotypic behaviors described, the spasmodic upper-body squeeze or "self-hug" seems to be highly associated with SMS. The finger lick and page flipping ("lick and flip") behavior may be less prevalent than initially reported. An underlying developmental asynchrony, specifically between intellectual functioning and emotional maturity, may also contribute to maladaptive behaviors in people with SMS. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1310]
Pantothenate Kinase-Associated Neurodegeneration
Pantothenate kinase-associated neurodegeneration (PKAN) is a form of neurodegeneration with brain iron accumulation, or NBIA (formerly called Hallervorden-Spatz syndrome). PKAN is characterized by progressive dystonia and basal ganglia iron deposition with onset that usually occurs before age ten years. Commonly associated features include dysarthria, rigidity, and pigmentary retinopathy. Approximately 25% of affected individuals have an 'atypical' presentation with later onset (age >10 years), prominent speech defects, psychiatric disturbances, and more gradual progression of disease. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1490]
Hyperkalemic periodic paralysis type 1 (hyperPP1) is characterized by attacks of flaccid limb weakness (which may also include weakness of the muscles of the eyes, throat, and trunk), hyperkalemia (serum potassium concentration >5 mmol/L) or an increase of serum potassium concentration of at least 1.5 mmol/L during an attack of weakness and/or provoking/worsening of an attack by oral potassium intake, normal serum potassium and muscle strength between attacks, onset before age 20 years, and absence of paramyotonia (muscle stiffness aggravated by cold and exercise). The attacks of flaccid muscle weakness usually begin in the first decade of life. Initially infrequent, the attacks then increase in frequency and severity over time until approximately age 50 years, after which the frequency of attacks declines considerably. Potassium-rich food or rest after exercise may precipitate an attack. A cold environment and emotional stress provoke or worsen the attacks. A spontaneous attack commonly starts in the morning before breakfast, lasts for 15 minutes to one hour, and then disappears. Cardiac arrhythmia or respiratory insufficiency usually does not occur during attacks. Between attacks, hyperPP1 is usually associated with mild myotonia (muscle stiffness) that does not impede voluntary movements. Many older affected individuals develop a chronic progressive myopathy. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1496]
Waardenburg syndrome type I (WS1) is an auditory-pigmentary disorder comprising congenital sensorineural hearing loss and pigmentary disturbances of the iris, hair, and skin, along with dystopia canthorum (lateral displacement of the inner canthi). The hearing loss in WS1, observed in approximately 60% of affected individuals, is congenital, typically non-progressive, either unilateral or bilateral, and sensorineural. Most commonly, hearing loss in WS1 is bilateral and profound (>100 dB). The majority of individuals with WS1 have either a white forelock or early graying of the scalp hair before age 30 years. The classic white forelock observed in approximately 45% of individuals is the most common hair pigmentation anomaly seen in WS1. Affected individuals may have complete heterochromia iridium, partial/segmental heterochromia, or hypoplastic or brilliant blue irides. Congenital leukoderma is frequently seen on the face, trunk, or limbs. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1531]
Fibrous Dysplasia/McCune-Albright Syndrome
Fibrous dysplasia/McCune-Albright syndrome (FD/MAS), the result of an early embryonic postzygotic somatic activating mutation of GNAS (encoding the cAMP pathway-associated G-protein, Gsα), is characterized by involvement of the skin, skeleton, and certain endocrine organs. However, because Gsα signaling is ubiquitous additional tissues may be affected. Gonadotropin-independent precocious puberty resulting from recurrent ovarian cysts in girls and autonomous testosterone production in boys; Testicular lesions with or without associated gonadotropin-independent precocious puberty; Thyroid lesions with or without non-autoimmune hyperthyroidism; Growth hormone excess; FGF23-mediated phosphate wasting with or without hypophosphatemia in association with fibrous dysplasia; and Neonatal hypercortisolism. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK274564]
Riboflavin Transporter Deficiency Neuronopathy
Riboflavin transporter deficiency neuronopathy is characterized by motor neuronopathy (manifest as proximal and distal limb weakness, often with severe distal wasting and breathing problems due to paralysis of the diaphragm), sensory neuronopathy (manifest as gait ataxia), and cranial neuronopathy (manifest as optic atrophy, sensorineural deafness, and bulbar palsy). Onset is usually in infancy or in childhood before age eight years; however, on occasion individuals with genetically proven disease present in the third decade. When untreated, most infants with riboflavin transporter deficiency rapidly become ventilator dependent and die in the first years of life. In the majority of affected individuals the initial finding is sensorineural deafness, which is usually progressive and severe. The time between the onset of deafness and the development of other manifestations varies but is usually one to two years. In some individuals an inter-current event, usually an injury or infection, appears to precipitate the initial manifestations or worsen existing findings. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK299312]
Best vitelliform macular dystrophy is a slowly progressive macular dystrophy with onset generally in childhood and sometimes in later teenage years. Affected individuals initially have normal vision followed by decreased central visual acuity and metamorphopsia. Individuals retain normal peripheral vision and dark adaptation. Age of onset and severity of vision loss show inter- and intrafamilial variability. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1167]
GNE-related myopathy, also known as inclusion body myopathy 2, is characterized by slowly progressive distal muscle weakness that begins in the late teens to early adult years with gait disturbance and foot drop secondary to anterior tibialis muscle weakness. Weakness eventually includes the hand and thigh muscles but commonly spares the quadriceps muscles, even in advanced disease. Affected individuals are usually wheelchair bound about 20 years after onset. If quadriceps sparing is incomplete, loss of ambulation tends to occur earlier. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1262]
Nonsyndromic Hearing Loss and Deafness, DFNB1
Nonsyndromic hearing loss and deafness (DFNB1) is characterized by congenital, non-progressive, mild-to-profound sensorineural hearing impairment. No other associated medical findings are present. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1272]
Coffin-Lowry syndrome (CLS) is usually characterized by severe-to-profound intellectual disability in males; less severely impaired individuals have been reported. Intellect ranges from normal to profoundly impaired in heterozygous females. The facial appearance is characteristic in the affected, older male child or adult. The hands are short, soft, and fleshy, often with remarkably hyperextensible fingers that taper from wide (proximally) to narrow with small terminal phalanges and nails. Males are consistently below the third centile in height. Microcephaly is common. Cardiac abnormalities may be present and can contribute to premature death. Stimulus-induced drop attacks (SIDAs) in which unexpected tactile or auditory stimuli or excitement triggers a brief collapse but no loss of consciousness are present in approximately 20% of affected individuals. Typically SIDAs begin between mid-childhood and the teens. Progressive kyphoscoliosis is one of the most difficult aspects of long-term care. Life span may be reduced. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1346]
GATA1-related cytopenia is characterized by thrombocytopenia and/or anemia ranging from mild to severe. One or more of the following may also be present: platelet dysfunction, mild β-thalassemia, neutropenia, and congenital erythropoietic porphyria (CEP) in males. Thrombocytopenia typically presents in infancy as a bleeding disorder with easy bruising and mucosal bleeding (e.g., epistaxis). Anemia ranges from minimal (mild dyserythropoiesis) to severe (hydrops fetalis requiring in utero transfusion). At the extreme end of the clinical spectrum, severe hemorrhage and/or erythrocyte transfusion dependence are life long; at the milder end, anemia and the risk for bleeding decrease spontaneously with age. Female carriers may have mild to moderate symptoms, such as menorrhagia. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1364]
Alpha-mannosidosis encompasses a continuum of clinical findings from mild to severe. Three clinical subtypes include:A mild form recognized after age ten years with absence of skeletal abnormalities, myopathy, and slow progression (type 1); A moderate form recognized before age ten years with presence of skeletal abnormalities, myopathy, and slow progression (type 2); and A severe form manifested as prenatal loss or early death from progressive central nervous system involvement (type 3). [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1396]
Peroxisome biogenesis disorders, Zellweger syndrome spectrum (PBD, ZSS) is a continuum of three phenotypes — Zellweger syndrome (ZS), the most severe; neonatal adrenoleukodystrophy (NALD); and infantile Refsum disease (IRD), the least severe — that were originally described before the biochemical and molecular bases of these disorders had been fully determined. Individuals with PBD, ZSS usually come to clinical attention in the newborn period or later in childhood. In the newborn period, affected children are hypotonic, feed poorly, and have distinctive facies, seizures, and liver cysts with hepatic dysfunction. Bony stippling (chondrodysplasia punctata) of the patella(e) and other long bones may occur. Infants with ZS are significantly impaired and typically die during the first year of life, usually having made no developmental progress. Older children have retinal dystrophy, sensorineural hearing loss, developmental delay with hypotonia, and liver dysfunction. The clinical courses of NALD and IRD are variable and may include developmental delays, hearing loss, vision impairment, liver dysfunction, episodes of hemorrhage, and intracranial bleeding. While some children can be very hypotonic, others learn to walk and talk. The condition is often slowly progressive. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1448]
CSF1R-Related Adult-Onset Leukoencephalopathy with Axonal Spheroids and Pigmented Glia
Adult-onset leukoencephalopathy with axonal spheroids and pigmented glia (ALSP), which includes both hereditary diffuse leukoencephalopathy with spheroids (HDLS) and pigmentary orthochromatic leukodystrophy (POLD), is characterized by executive dysfunction, memory decline, personality changes, motor impairments, and seizures. A frontal lobe syndrome (e.g., loss of judgment, lack of social inhibitors, lack of insight, and motor persistence) usually appears early in the disease course. The mean age of onset is usually in the fourth decade. Affected individuals eventually become bedridden with spasticity and rigidity. The disease course ranges from two to 30 or more years (mean: 8 years). [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK100239]
Nevoid basal cell carcinoma syndrome (NBCCS) is characterized by the development of multiple jaw keratocysts, frequently beginning in the second decade of life, and/or basal cell carcinomas (BCCs) usually from the third decade onward. Approximately 60% of individuals have a recognizable appearance with macrocephaly, frontal bossing, coarse facial features, and facial milia. Most individuals have skeletal anomalies (e.g., bifid ribs, wedge-shaped vertebrae). Ectopic calcification, particularly in the falx, is present in more than 90% of affected individuals by age 20 years. Cardiac and ovarian fibromas occur in approximately 2% and 20% of individuals respectively. Approximately 5% of all children with NBCCS develop medulloblastoma (primitive neuroectodermal tumor [PNET]), generally the desmoplastic subtype. The risk of developing medulloblastoma is substantially higher in individuals with an SUFU pathogenic variant (33%) than in those with a PTCH1 pathogenic variant (<2%). Peak incidence is at age one to two years. Life expectancy in NBCCS is not significantly different from average. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1151]
Epidermolysis Bullosa with Pyloric Atresia
Epidermolysis bullosa with pyloric atresia (EB-PA) is characterized by fragility of the skin and mucous membranes, manifested by blistering with little or no trauma; congenital pyloric atresia; and ureteral and renal anomalies (dysplastic/multicystic kidney, hydronephrosis/hydroureter, ureterocele, duplicated renal collecting system, absent bladder). The course of EB-PA is usually severe and often lethal in the neonatal period. Most affected children succumb as neonates; those who survive may have severe blistering with formation of granulation tissue on the skin around the mouth, nose, fingers, and toes, and internally around the trachea. However, some affected individuals have little or no blistering later in life. Additional features shared by EB-PA and the other major forms of EB include congenital localized absence of skin (aplasia cutis congenita) affecting the extremities and/or head, milia, nail dystrophy, scarring alopecia, hypotrichosis, contractures, and dilated cardiomyopathy. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1157]
Ehlers-Danlos syndrome (EDS), hypermobility type is generally considered the least severe type of EDS, although significant complications, primarily musculoskeletal, can and do occur. The skin is often soft or velvety and may be mildly hyperextensible. Subluxations and dislocations are common; they may occur spontaneously or with minimal trauma and can be acutely painful. Degenerative joint disease is common. Chronic pain, distinct from that associated with acute dislocations, is a serious complication of the condition and can be both physically and psychologically disabling. Easy bruising is common. Functional bowel disorders are likely underrecognized. Autonomic dysfunction, such as orthostatic intolerance, may also be seen. Aortic root dilation is typically of a mild degree with no increased risk of dissection in the absence of significant dilation. Psychological dysfunction, psychosocial impairment, and emotional problems are common. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1279]
PROP1-Related Combined Pituitary Hormone Deficiency
PROP1-related combined pituitary hormone deficiency (CPHD) is associated with deficiencies of growth hormone (GH); thyroid-stimulating hormone (TSH); the two gonadotropins, luteinizing hormone (LH) and follicle-stimulating hormone (FSH); prolactin (PrL); and occasionally adrenocorticotropic hormone (ACTH). Most affected individuals are ascertained because of growth failure and failure to thrive starting in infancy or early childhood (approximate age range: 9 months to 8 years). Hypothyroidism is usually mild and occurs in later infancy and childhood. Affected individuals can have absent or delayed and incomplete secondary sexual development with infertility. Untreated males usually have a small penis and small testes. Some females experience menarche, but subsequently require hormone replacement therapy. ACTH deficiency is less common and, when present, usually occurs in adolescence or adulthood. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1347]
Nonsyndromic Hearing Loss and Deafness, DFNA3
Nonsyndromic hearing loss and deafness, DFNA3, is characterized by pre- or postlingual, mild to profound, progressive high-frequency sensorineural hearing impairment. Affected individuals have no other associated medical findings. Most individuals diagnosed as having DFNA3 have a deaf parent; the family history is rarely negative. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1536]
PINK1 Type of Young-Onset Parkinson Disease
The PINK1 type of young-onset Parkinson disease is characterized by variable combinations of rigidity, bradykinesia, and rest tremor, often making it clinically indistinguishable from idiopathic Parkinson disease. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK26472]
The spectrum of CDC73-related disorders includes the following phenotypes:Hyperparathyroidism-jaw tumor syndrome (HPT-JT) Parathyroid carcinoma Familial isolated hyperparathyroidism (FIHP) [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK3789]
Childhood Ataxia with Central Nervous System Hypomyelination/Vanishing White Matter
Childhood ataxia with central nervous system hypomyelination/vanishing white matter disease (CACH/VWM) is characterized by ataxia, spasticity, and variable optic atrophy. The phenotypic range includes a prenatal/congenital form, a subacute infantile form (onset age <1 year), an early childhood onset form (onset age 1-5 years), a late childhood /juvenile onset form (onset age 5-15 years), and an adult onset form. The prenatal/congenital form is characterized by severe encephalopathy. In the later onset forms initial motor and intellectual development is normal or mildly delayed followed by neurologic deterioration with a chronic progressive or subacute course. Chronic progressive decline can be exacerbated by rapid deterioration during febrile illnesses or following head trauma or major surgical procedures, or by acute psychological stresses such as extreme fright. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1258]
Familial hemiplegic migraine (FHM) falls within the category of migraine with aura. In migraine with aura (including familial hemiplegic migraine) the neurologic symptoms of aura are unequivocally localizable to the cerebral cortex or brain stem and include visual disturbance (most common), sensory loss (e.g., numbness or paresthesias of the face or an extremity), and dysphasia (difficulty with speech); FHM must include motor involvement, i.e., hemiparesis (weakness of an extremity). Hemiparesis occurs with at least one other symptom during FHM aura. Neurologic deficits with FHM attacks can be prolonged for hours to days and may outlast the associated migrainous headache. FHM is often earlier in onset than typical migraine, frequently beginning in the first or second decade; the frequency of attacks tends to decrease with age. Approximately 40%-50% of families with FHM1 have cerebellar signs ranging from nystagmus to progressive, usually late-onset mild ataxia. Cerebral infarction and death have rarely been associated with hemiplegic migraine. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1388]
Heritable Pulmonary Arterial Hypertension
Pulmonary arterial hypertension (PAH) is characterized by widespread obstruction and obliteration of the smallest pulmonary arteries. When a sufficient number of vessels are occluded, the resistance to blood flow through the lungs increases, and the right ventricle attempts to compensate by generating higher pressure to maintain pulmonary blood flow. When the right ventricle can no longer compensate for the increased resistance, progressive heart failure ensues. Initial symptoms include dyspnea (60%), fatigue (19%), syncope (8%), chest pain (7%), palpitations (5%), and leg edema (3%). All ages are affected, but the mean age at diagnosis is 36 years. Mean survival after diagnosis is 2.8 years; current therapy does improve clinical function but has modest effect on survival. The term heritable PAH (HPAH) includes familial PAH (PAH that occurs in two or more family members) and simplex PAH (i.e., a single occurrence in a family) when a pathogenic variant has been identified. Most heritable PAH (75%) is caused by a pathogenic variant in BMPR2; pathogenic variants in other genes (i.e., ACVRL1, KCNK3, CAV1, SMAD9, BMPR1B,) are considerably less common (1-3%). HPAH has identical symptoms, signs, and histology as PAH of unknown cause. The time from onset of symptoms to diagnosis may be shorter in individuals with familial PAH, possibly because of familial awareness of the disease. Three retrospective studies suggest that persons with PAH who have a BMPR2 pathogenic variant exhibit more severe disease. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1485]
Collagen type VI-related disorders represent a continuum of overlapping phenotypes with Bethlem myopathy at the mild end, Ullrich congenital muscular dystrophy (CMD) at the severe end, and two rare, less well-defined disorders – autosomal dominant limb-girdle muscular dystrophy and autosomal recessive myosclerosis myopathy – in between. Although Bethlem myopathy and Ullrich CMD were defined long before their molecular basis was known, they remain useful for clarification of prognosis and management. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1503]
KCNQ2-related disorders represent a continuum of overlapping neonatal epileptic phenotypes caused by a heterozygous mutation in KCNQ2. The clinical features of KCNQ2-related disorders range from KCNQ2-related benign familial neonatal epilepsy (KCNQ2-BFNE) at the mild end to KCNQ2-related epileptic encephalopathy (KCNQ2-NEE) at the severe end. KCNQ2-BFNE is characterized by a wide spectrum of seizure types (tonic or apneic episodes, focal clonic activity, or autonomic changes) that start in otherwise healthy infants between the second and eighth day of life and spontaneously disappear between the first and the sixth to 12th month of life. Motor activity may be confined to one body part, migrate to other body regions, or generalize. Seizures are generally brief, lasting one to two minutes. Rarely, KCNQ2-BFNE may evolve into status epilepticus. About 10%-15% of individuals with BFNS develop epileptic seizures later in life. KCNQ2-NEE is characterized by multiple daily seizures beginning in the first week of life that are mostly tonic, with motor and autonomic features. Seizures cease between ages nine months and four years. At onset, EEG shows a burst-suppression pattern or multifocal epileptiform activity; early brain MRI shows basal ganglia and thalamic hyperintensities that later resolved. Most affected individuals are profoundly intellectually impaired and have axial hypotonia and/or spastic quadriplegia. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK32534]
Cartilage-Hair Hypoplasia - Anauxetic Dysplasia Spectrum Disorders
The cartilage-hair hypoplasia – anauxetic dysplasia (CHH-AD) spectrum disorders are a continuum that includes the following phenotypes:Metaphyseal dysplasia without hypotrichosis (MDWH) Cartilage-hair hypoplasia (CHH) Anauxetic dysplasia (AD) [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK84550]
Holt-Oram syndrome (HOS) is characterized by:Upper-extremity malformations involving radial, thenar, or carpal bones; and Variably, one or both of the following:Personal and/or family history of congenital heart malformation, most commonly ostium secundum atrial septal defect (ASD) and ventricular septal defect (VSD), especially those occurring in the muscular trabeculated septumCardiac conduction disease Personal and/or family history of congenital heart malformation, most commonly ostium secundum atrial septal defect (ASD) and ventricular septal defect (VSD), especially those occurring in the muscular trabeculated septum Cardiac conduction disease [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1111]
Juvenile hemochromatosis is characterized by onset of severe iron overload occurring typically in the first to third decades of life. Males and females are equally affected. Prominent clinical features include hypogonadotropic hypogonadism, cardiomyopathy, arthropathy, and liver fibrosis or cirrhosis. Hepatocellular cancer has not been reported. The main cause of death is cardiac disease. If juvenile hemochromatosis is detected early enough and if blood is removed regularly through the process of phlebotomy to achieve iron depletion, morbidity and mortality are greatly reduced. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1170]
Fukuyama congenital muscular dystrophy (FCMD) is characterized by hypotonia, symmetric generalized muscle weakness, and CNS migration disturbances that result in changes consistent with cobblestone (previously type II) lissencephaly with cerebral and cerebellar cortical dysplasia. Mild, typical, and severe phenotypes are recognized. Onset typically occurs in early infancy, with a poor suck, weak cry, and floppiness. Affected individuals have contractures of the hips, knees, and interphalangeal joints. Later features include myopathic facial appearance, pseudohypertrophy of the calves and forearms, motor and speech retardation, intellectual disability, seizures, ophthalmologic abnormalities including visual impairment and retinal dysplasia, and progressive cardiac involvement in individuals older than age ten years. Swallowing disturbance occurs in individuals with severe FCMD and in individuals older than age ten years, leading to recurrent aspiration pneumonia and death. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1206]
Y chromosome infertility is characterized by azoospermia (absence of sperm), severe oligozoospermia (<1 x 106 sperm/mL semen), moderate oligozoospermia (1-5 x 106 sperm/mL semen), or mild oligozoospermia (5-20 x 106 sperm/mL semen). Males with Y chromosome infertility usually have no obvious symptoms, although physical examination may reveal small testes. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1339]
Hereditary Neuropathy with Liability to Pressure Palsies
Hereditary neuropathy with liability to pressure palsies (HNPP) is characterized by repeated focal pressure neuropathies such as carpal tunnel syndrome and peroneal palsy with foot drop. The first attack usually occurs in the second or third decade. Recovery from acute neuropathy is often complete; when recovery is not complete, the resulting disability is usually mild. Some affected individuals also have signs of a mild to moderate peripheral neuropathy. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1392]
Pendred Syndrome/Nonsyndromic Enlarged Vestibular Aqueduct
Pendred syndrome (PDS) and DFNB4 comprise a phenotypic spectrum of hearing loss with or without other findings. Pendred syndrome is characterized by: severe-to-profound bilateral sensorineural hearing impairment that is usually congenital (or prelingual) and non-progressive; vestibular dysfunction; temporal bone abnormalities; and development of euthyroid goiter in late childhood to early adulthood. Variability of findings is considerable, even within the same family. DFNB4 is characterized by nonsyndromic sensorineural hearing impairment, vestibular dysfunction, and enlarged vestibular aqueduct (EVA). Thyroid defects are not seen in DFNB4. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1467]
The PTEN hamartoma tumor syndrome (PHTS) includes Cowden syndrome (CS), Bannayan-Riley-Ruvalcaba syndrome (BRRS), PTEN-related Proteus syndrome (PS), and Proteus-like syndrome.CS is a multiple hamartoma syndrome with a high risk for benign and malignant tumors of the thyroid, breast, and endometrium. Affected individuals usually have macrocephaly, trichilemmomas, and papillomatous papules, and present by the late 20s. The lifetime risk of developing breast cancer is 85%, with an average age of diagnosis between 38 and 46 years. The lifetime risk for thyroid cancer (usually follicular, rarely papillary, but never medullary thyroid cancer) is approximately 35%. The risk for endometrial cancer, although not well defined, may approach 28%. BRRS is a congenital disorder characterized by macrocephaly, intestinal hamartomatous polyposis, lipomas, and pigmented macules of the glans penis. PS is a complex, highly variable disorder involving congenital malformations and hamartomatous overgrowth of multiple tissues, as well as connective tissue nevi, epidermal nevi, and hyperostoses. Proteus-like syndrome is undefined but refers to individuals with significant clinical features of PS who do not meet the diagnostic criteria for PS. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1488]
The NSDHL-related disorders include: CHILD (congenital hemidysplasia with ichthyosiform nevus and limb defects) syndrome, an X-linked dominant condition that is usually male lethal during gestation and thus predominantly affects females; and CK syndrome, an X-linked recessive disorder that affects males. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK51754]
X-Linked Otopalatodigital Spectrum Disorders
The otopalatodigital (OPD) spectrum disorders, characterized primarily by skeletal dysplasia, include the following: Otopalatodigital syndrome type I (OPD1) Otopalatodigital syndrome type II (OPD2) Frontometaphyseal dysplasia (FMD) Melnick-Needles syndrome (MNS) Terminal osseous dysplasia with pigmentary skin defects (TODPD) [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1393]
Episodic ataxia type 2 (EA2) is characterized by paroxysmal attacks of ataxia, vertigo, and nausea typically lasting minutes to days in duration. Attacks can be associated with dysarthria, diplopia, tinnitus, dystonia, hemiplegia, and headache. About 50% of individuals with EA2 have migraine headaches. Onset is typically in childhood or early adolescence (age range 2-32 years). Frequency of attacks can range from once or twice a year to three or four times a week. Attacks can be triggered by stress, exertion, caffeine, alcohol, fever, heat, and phenytoin; they can be stopped or decreased in frequency and severity by administration of acetazolamide or 4-aminopyridine. Between attacks, individuals may initially be asymptomatic but commonly develop interictal findings that can include nystagmus, pursuit and saccade alterations, and ataxia. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1501]
PRSS1-related hereditary pancreatitis (HP) is characterized by inflammation of the pancreas that progresses from acute (sudden onset; duration <6 months) to recurrent acute (>1 episode of acute pancreatitis) to chronic (duration >6 months). The range of symptoms and disease course vary from person to person. On average, acute pancreatitis occurs by age ten years and chronic pancreatitis by age 20 years. Manifestations of acute pancreatitis can range from vague abdominal pain lasting one to three days to severe abdominal pain lasting days to weeks and requiring hospitalization. Chronic pancreatitis typically manifests as episodic or continuous mild to severe abdominal pain, exocrine pancreatic insufficiency leading to maldigestion, and pancreatic endocrine insufficiency (glucose intolerance progressing to type I diabetes mellitus). The risk for pancreatic cancer increases after age 50 years. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK84399]
Dystonia is a movement disorder characterized by sustained or intermittent muscle contractions causing abnormal, often repetitive movements and/or postures. Dystonic movements are typically patterned and twisting, and may be associated with tremor. Dystonia is often initiated or worsened by voluntary action and associated with overflow muscle activation. Dystonia can be classified clinically according to age of onset, body distribution, temporal pattern, and associated features (i.e., isolated dystonia – in which it is the only motor feature except tremor; combined dystonia – in which another movement disorder is present; or complex dystonia – in which other neurologic or systemic manifestations are present). [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1155]
Costello syndrome is characterized by failure to thrive in infancy as a result of severe postnatal feeding difficulties; short stature; developmental delay or intellectual disability; coarse facial features (full lips, large mouth, full nasal tip); curly or sparse, fine hair; loose, soft skin with deep palmar and plantar creases; papillomata of the face and perianal region; diffuse hypotonia and joint laxity with ulnar deviation of the wrists and fingers; tight Achilles tendons; and cardiac involvement including: cardiac hypertrophy (usually typical hypertrophic cardiomyopathy [HCM]), congenital heart defect (usually valvar pulmonic stenosis), and arrhythmia (usually supraventricular tachycardia, especially chaotic atrial rhythm/multifocal atrial tachycardia or ectopic atrial tachycardia). Relative or absolute macrocephaly is typical, and postnatal cerebellar overgrowth can result in the development of a Chiari I malformation with associated anomalies including hydrocephalus or syringomyelia. Individuals with Costello syndrome have an approximately 15% lifetime risk for malignant tumors including rhabdomyosarcoma and neuroblastoma in young children and transitional cell carcinoma of the bladder in adolescents and young adults. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1507]
The TRPV4-associated disorders (previously considered to be clinically distinct phenotypes before their molecular basis was discovered) are now grouped into neuromuscular disorders and skeletal dysplasias; however, the overlap within and between both groups is considerable. Bilateral progressive sensorineural hearing loss (SNHL) can occur in both. Charcot-Marie-Tooth disease type 2C (CMT2C) Scapuloperoneal spinal muscular atrophy (SPSMA) Congenital distal spinal muscular atrophy (CDSMA) [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK201366]
21-Hydroxylase-Deficient Congenital Adrenal Hyperplasia
21-hydroxylase deficiency (21-OHD) is the most common cause of congenital adrenal hyperplasia (CAH), a family of autosomal recessive disorders involving impaired synthesis of cortisol from cholesterol by the adrenal cortex. In 21-OHD CAH, excessive adrenal androgen biosynthesis results in virilization in all individuals and salt wasting in some individuals. A classic form with severe enzyme deficiency and prenatal onset of virilization is distinguished from a non-classic form with mild enzyme deficiency and postnatal onset. The classic form is further divided into the simple virilizing form (~25% of affected individuals) and the salt-wasting form, in which aldosterone production is inadequate (≥75% of individuals). Newborns with salt-wasting 21-OHD CAH are at risk for life-threatening salt-wasting crises. Individuals with the non-classic form of 21-OHD CAH present postnatally with signs of hyperandrogenism; females with the non-classic form are not virilized at birth. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1171]
Congenital Fibrosis of the Extraocular Muscles
Congenital fibrosis of the extraocular muscles (CFEOM) refers to at least seven genetically defined strabismus syndromes: CFEOM1A, CFEOM1B, CFEOM2, CFEOM3A, CFEOM3B, CFEOM3C, and Tukel syndrome, characterized by congenital non-progressive ophthalmoplegia (inability to move the eyes) with or without ptosis (droopy eyelids) affecting part or all of the oculomotor nucleus and nerve (cranial nerve III) and its innervated muscles (superior, medial, and inferior recti, inferior oblique, and levator palpabrae superioris) and/or the trochlear nucleus and nerve (cranial nerve IV) and its innervated muscle (the superior oblique). In general, affected individuals have severe limitation of vertical gaze (usually upgaze) and variable limitation of horizontal gaze. Individuals with CFEOM frequently compensate for the ophthalmoplegia by maintaining abnormal head positions at rest and by moving their heads rather than their eyes to track objects. Individuals with CFEOM3A may also have intellectual disability, social disability, facial weakness, and/or a progressive axonal peripheral neuropathy (a form of Charcot-Marie-Tooth disease). Individuals with CFEOM3C also have intellectual disability and facial dysmorphism reminiscent of Albright hereditary osteodystrophy-like syndrome. Individuals with Tukel syndrome also have postaxial oligodactyly or oligosyndactyly of the hands. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1348]
Autosomal Recessive Congenital Ichthyosis
Autosomal recessive congenital ichthyosis (ARCI) encompasses several forms of nonsyndromic ichthyosis. Although most neonates with ARCI are collodion babies, the clinical presentation and severity of ARCI may vary significantly, ranging from harlequin ichthyosis, the most severe and often fatal form, to lamellar ichthyosis (LI) and (nonbullous) congenital ichthyosiform erythroderma (CIE). These phenotypes are now recognized to fall on a continuum; however, the phenotypic descriptions are clinically useful for clarification of prognosis and management. Infants with harlequin ichthyosis are usually born prematurely and are encased in thick, hard, armor-like plates of cornified skin that severely restrict movement. Life-threatening complications in the immediate postnatal period include respiratory distress, feeding problems, and systemic infection. Collodion babies are born with a taut, shiny, translucent or opaque membrane that encases the entire body and lasts for days to weeks. LI and CIE are seemingly distinct phenotypes: classic, severe lamellar ichthyosis (LI) with dark brown, plate-like scale with no erythroderma and CIE with finer whiter scale and underlying generalized redness of the skin. Affected individuals with severe involvement can have ectropion, eclabium, scarring alopecia involving the scalp and eyebrows, and palmar and plantar keratoderma. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1420]
Classic Galactosemia and Clinical Variant Galactosemia
The term galactosemia refers to disorders of galactose metabolism that include classic galactosemia, clinical variant galactosemia, and biochemical variant galactosemia. This GeneReview focuses on: Classic galactosemia, which can result in life-threatening complications including feeding problems, failure to thrive, hepatocellular damage, bleeding, and E. coli sepsis in untreated infants. If a lactose-restricted diet is provided during the first ten days of life, the neonatal signs usually quickly resolve and the complications of liver failure, sepsis, and neonatal death are prevented; however, despite adequate treatment from an early age, children with classic galactosemia remain at increased risk for developmental delays, speech problems (termed childhood apraxia of speech and dysarthria), and abnormalities of motor function. Almost all females with classic galactosemia manifest premature ovarian insufficiency (POI). Clinical variant galactosemia, which can result in life-threatening complications including feeding problems, failure to thrive, hepatocellular damage including cirrhosis and bleeding in untreated infants. This is exemplified by the disease that occurs in African Americans and native Africans in South Africa. Persons with clinical variant galactosemia may be missed with newborn screening (NBS) as the hypergalactosemia is not as marked as in classic galactosemia and breath testing is normal. If a lactose-restricted diet is provided during the first ten days of life, the severe acute neonatal complications are usually prevented. African Americans with clinical variant galactosemia and adequate early treatment do not appear to be at risk for long-term complications including POI. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1518]
CHARGE is a mnemonic for coloboma, heart defects, choanal atresia, retarded growth and development, genital abnormalities, and ear anomalies. CHARGE syndrome is characterized by the following:Unilateral or bilateral coloboma of the iris, retina-choroid, and/or disc with or without microphthalmos (80%-90% of individuals) Unilateral or bilateral choanal atresia or stenosis (50%-60%) Cranial nerve dysfunction resulting in hyposmia or anosmia, unilateral or bilateral facial palsy (40%), impaired hearing, and/or swallowing problems (70%-90%) Abnormal outer ears, ossicular malformations, Mondini defect of the cochlea and absent or hypoplastic semicircular canals (>90%) Cryptorchidism in males and hypogonadotrophic hypogonadism in both males and females Developmental delay Cardiovascular malformations (75%-85%) Growth deficiency (70%-80%) Orofacial clefts (15%-20%) Tracheoesophageal fistula (15%-20%) [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1117]
DCX-related disorders include the neuronal migration disorders classic lissencephaly (formerly also known as lissencephaly type 1), usually in males; and subcortical band heterotopia (SBH, also called double cortex), primarily in females. Males with classic DCX-related lissencephaly typically have severe and global developmental delay, infantile-onset seizures (infantile spasms, West syndrome, focal and generalized seizures), and severe intellectual disability. In individuals with SBH, cognitive abilities range from normal to learning disabilities and/or severe intellectual disability. The majority of individuals with SBH present with focal or generalized seizures. Behavior problems may also be observed. In DCX-related lissencephaly and SBH the severity of the clinical manifestation correlates with the degree of the underlying brain malformation. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1185]
Cranioectodermal dysplasia (CED), a ciliopathy also known as Sensenbrenner syndrome, is a multi-system disorder with skeletal involvement (narrow thorax, shortened proximal limbs, and brachydactyly), ectodermal features (widely-spaced hypoplastic teeth, hypodontia, sparse hair, skin laxity, abnormal nails), joint laxity, growth retardation, and characteristic facial features (frontal bossing, low-set simple ears, high forehead, telecanthus/epicanthus, full cheeks, everted lower lip). Most affected children develop nephronophthisis that often leads to end-stage renal disease (ESRD) in infancy or childhood, a major cause of morbidity and mortality. Hepatic fibrosis and retinal dystrophy, other manifestations of ciliopathies, are also observed. Dolichocephaly, often secondary to sagittal craniosynostosis, is a primary manifestation that distinguishes CED from most other ciliopathies. Brain malformations and developmental delay may also occur. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK154653]
Diamond-Blackfan anemia (DBA) in its classic form is characterized by a profound isolated normochromic and usually macrocytic anemia with normal leukocytes and platelets, congenital malformations in approximately 50% of affected individuals, and growth retardation in 30% of affected individuals. The hematologic complications occur in 90% of affected individuals during the first year of life (median age of onset: 2 months). Eventually, 40% of affected individuals are corticosteroid dependent, 40% are transfusion dependent, and 20% go into remission. The phenotypic spectrum ranges from a mild form (e.g., mild anemia; no anemia with only subtle erythroid abnormalities; physical malformations without anemia) to a severe form of fetal anemia resulting in nonimmune hydrops fetalis. DBA is associated with an increased risk for acute myelogenous leukemia (AML), myelodysplastic syndrome (MDS), and solid tumors including osteogenic sarcoma. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK7047]
Spinocerebellar ataxia type 7 (SCA7) is characterized by progressive cerebellar ataxia, including dysarthria and dysphagia, and cone-rod and retinal dystrophy with progressive central visual loss resulting in blindness in affected adults. Onset in early childhood or infancy has an especially rapid and aggressive course often associated with failure to thrive and regression of motor milestones. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1256]
Mucopolysaccharidosis type I (MPS I) is a progressive multisystem disorder with features ranging over a continuum of severity. While affected individuals have traditionally been classified as having one of three MPS I syndromes, Hurler syndrome, Hurler-Scheie syndrome, or Scheie syndrome, no biochemical differences have been identified and the clinical findings overlap; thus, affected individuals are best described as having either severe or attenuated MPS I, a distinction that influences therapeutic options.Severe MPS I. Infants appear normal at birth. Typical early manifestations are nonspecific (e.g., umbilical or inguinal hernia, frequent upper respiratory-tract infections before age 1 year). Coarsening of the facial features may not become apparent until after age one year. Gibbus deformity of the lower spine is common. Progressive skeletal dysplasia (dysostosis multiplex) involving all bones is universal. By age three years, linear growth ceases. Intellectual disability is progressive and profound. Hearing loss is common. Death, typically caused by cardiorespiratory failure, usually occurs within the first ten years of life. Attenuated MPS I. The severity and rate of disease progression range from serious life-threatening complications leading to death in the second to third decades to a normal life span complicated by significant disability from progressive joint manifestations. While some individuals have no neurologic involvement and psychomotor development may be normal in early childhood, learning disabilities can be present. Clinical onset is usually between ages three and ten years. Hearing loss and cardiac valvular disease are common. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1162]
Polycystic Lipomembranous Osteodysplasia with Sclerosing Leukoencephalopathy (PLOSL)
Polycystic lipomembranous osteodysplasia with sclerosing leukoencephalopathy (PLOSL) is characterized by fractures (resulting from radiologically demonstrable polycystic osseous lesions), frontal lobe syndrome, and progressive presenile dementia beginning in the fourth decade. The clinical course of PLOSL can be divided into four stages: (1) The latent stage is characterized by normal early development. (2) The osseous stage (3rd decade of life) is characterized by pain and tenderness, mostly in ankles and feet, usually following strain or injury. Fractures are typically diagnosed several years later, most commonly in the bones of the extremities. (3) In the early neurologic stage (4th decade of life), a change of personality begins to develop insidiously. Affected individuals show a frontal lobe syndrome (loss of judgment, euphoria, loss of social inhibitions, disturbance of concentration, and lack of insight, libido, and motor persistence) leading to serious social problems. (4) The late neurologic stage is characterized by progressive dementia and loss of mobility. Death usually occurs before age 50 years. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1197]
Oculocutaneous albinism type 2 (OCA2) is characterized by hypopigmentation of the skin and hair and the characteristic ocular changes found in all types of albinism, including nystagmus; reduced iris pigment with iris translucency; reduced retinal pigment with visualization of the choroidal blood vessels on ophthalmoscopic examination; foveal hypoplasia associated with reduction in visual acuity; and misrouting of the optic nerve fiber radiations at the chiasm, associated with strabismus, reduced stereoscopic vision, and altered visual evoked potentials (VEP). Individuals with OCA2 are usually recognized within the first three to six months of life because of the ocular features of visual inattention, nystagmus, and strabismus. Vision is stable to slowly improving after early childhood until mid- to late teens, and no major change or loss of established visual acuity occurs related to the albinism. The amount of cutaneous pigmentation in OCA2 ranges from minimal to near-normal compared to others of the same ethnic and family backgrounds. Newborns with OCA2 almost always have lightly pigmented hair, brows, and lashes, with color ranging from light yellow to blond to brown. Hair color may darken with age but does not vary substantially from adolescence to adulthood. Brown OCA, initially identified in Africans and African Americans with light brown hair and skin, is part of the spectrum of OCA2. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1232]
Polycystic Kidney Disease, Autosomal Recessive
Autosomal recessive polycystic kidney disease (ARPKD) belongs to a group of congenital hepatorenal fibrocystic syndromes and is a cause of significant renal and liver-related morbidity and mortality in children. The majority of individuals with ARPKD classically present in the neonatal period with enlarged echogenic kidneys. Renal disease is characterized by nephromegaly, hypertension, and varying degrees of renal dysfunction. More than 50% of children with ARPKD who have a classic presentation progress to end-stage renal disease (ESRD) within the first decade of life; ESRD may require kidney transplantation. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1326]
McLeod neuroacanthocytosis syndrome (designated as MLS throughout this review) is a multisystem disorder with central nervous system (CNS), neuromuscular, and hematologic manifestations in males. CNS manifestations are a neurodegenerative basal ganglia disease including (1) movement disorders, (2) cognitive alterations, and (3) psychiatric symptoms. Neuromuscular manifestations include a (mostly subclinical) sensorimotor axonopathy and muscle weakness or atrophy of different degrees. Hematologically, MLS is defined as a specific blood group phenotype (named after the first proband, Hugh McLeod) that results from absent expression of the Kx erythrocyte antigen and weakened expression of Kell blood group antigens. The hematologic manifestations are red blood cell acanthocytosis and compensated hemolysis. Allo-antibodies in the Kell and Kx blood group system can cause strong reactions to transfusions of incompatible blood and severe anemia in newborns of Kell-negative mothers. Females heterozygous for XK pathogenic variants have mosaicism for the Kell and Kx blood group antigens but usually lack CNS and neuromuscular manifestations; however, some heterozygous females may develop clinical manifestations including chorea or late-onset cognitive decline. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1354]
Adenosine deaminase (ADA) deficiency is a systemic purine metabolic disorder that primarily affects lymphocyte development, viability, and function. The clinical phenotypic spectrum includes: Severe combined immunodeficiency disease (SCID), often diagnosed by age six months and usually by age 12 months. Less severe "delayed" onset combined immune deficiency (CID), usually diagnosed between age one and ten years. "Late/adult onset" CID, diagnosed in the second to fourth decades. Benign "partial ADA deficiency" (very low or absent ADA activity in erythrocytes but greater ADA activity in nucleated cells), which is compatible with normal immune function. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1483]
The cerebral creatine deficiency syndromes (CCDS), inborn errors of creatine metabolism, include the two creatine biosynthesis disorders, guanidinoacetate methyltransferase (GAMT) deficiency and L-arginine:glycine amidinotransferase (AGAT or GATM) deficiency, and the creatine transporter (SLC6A8) deficiency. Intellectual disability and seizures are common to all three CCDS. The majority of individuals with GAMT deficiency have a behavior disorder that can include autistic behaviors and self-mutilation; a significant proportion have pyramidal/extrapyramidal findings. Onset is between ages three months and three years. Only seven individuals with AGAT deficiency have been reported. The phenotype of SLC6A8 deficiency in affected males ranges from mild intellectual disability and speech delay to severe intellectual disability, seizures, and behavior disorder; age at diagnosis ranges from two to 66 years. Females heterozygous for SLC6A8 deficiency may have learning and behavior problems. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK3794]
Autosomal Dominant Nocturnal Frontal Lobe Epilepsy
Autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE) is characterized by clusters of nocturnal motor seizures, which are often stereotyped and brief (5 seconds to 5 minutes). They vary from simple arousals from sleep to dramatic, often bizarre, hyperkinetic events with tonic or dystonic features. Affected individuals may experience aura. Retained awareness during seizures is common. A minority of individuals experience daytime seizures. Onset ranges from infancy to adulthood. About 80% of individuals develop ADNFLE in the first two decades of life; mean age of onset is ten years. Clinical neurologic examination is normal and intellect is usually preserved, but reduced intellect, psychiatric comorbidity, or cognitive deficits may occur. Within a family, the manifestations of the disorder may vary considerably. ADNFLE is lifelong but not progressive. As an individual reaches middle age, attacks may become milder and less frequent. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1169]
If untreated, young children with profound biotinidase deficiency usually exhibit neurologic abnormalities including seizures, hypotonia, ataxia, developmental delay, vision problems, hearing loss, and cutaneous abnormalities (e.g., alopecia, skin rash, candidiasis). Older children and adolescents with profound biotinidase deficiency often exhibit motor limb weakness, spastic paresis, and decreased visual acuity. Once vision problems, hearing loss, and developmental delay occur, they are usually irreversible, even with biotin therapy. Individuals with partial biotinidase deficiency may have hypotonia, skin rash, and hair loss, particularly during times of stress. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1322]
HFE-associated hereditary hemochromatosis (HFE-HH) is characterized by inappropriately high absorption of iron by the gastrointestinal mucosa. The phenotypic spectrum of HFE-HH is now recognized to include:Those with clinical HFE-HH, in which manifestations of end-organ damage secondary to iron storage are present; Those with biochemical HFE-HH, in which the only evidence of iron overload is increased transferrin-iron saturation and increased serum ferritin concentration; Non-expressing p.Cys282Tyr homozygotes, in whom neither clinical manifestations of HFE-HH nor iron overload is present. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1440]
Familial hypercholesterolemia (FH) is characterized by severely elevated LDL cholesterol (LDL-C) levels that cause atherosclerotic plaque deposition in arteries and a markedly increased risk of coronary artery disease at an early age. Cholesterol deposits are also sometimes found in the tendons (xanthomas) and/or around the eyes (xanthelasmas). In FH, the more common cardiovascular disease is coronary heart disease (CHD), which may manifest as angina and myocardial infarction; stroke occurs more rarely. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK174884]
WFS1-related disorders range from Wolfram syndrome (WFS) to WFS1-related low-frequency sensory hearing loss (also known as DFNA6/14/38 low-frequency sensorineural hearing loss [LFSNHL]). WFS is a progressive neurodegenerative disorder characterized by onset of diabetes mellitus and optic atrophy before age 16 years, and typically associated with sensorineural hearing loss, progressive neurologic abnormalities (cerebellar ataxia, peripheral neuropathy, dementia, psychiatric illness, and urinary tract atony), and other endocrine abnormalities. Median age at death is 30 years. WFS-like disease is characterized by sensorineural hearing loss, diabetes mellitus, psychiatric illness, and variable optic atrophy. WFS1-related LFSNHL is characterized by congenital, nonsyndromic, slowly progressive, low-frequency (<2000 Hz) sensorineural hearing loss. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK4144]
MUTYH-associated polyposis (MAP), caused by biallelic pathogenic variants in MUTYH, is characterized by a greatly increased lifetime risk of colorectal cancer (CRC) (43% to almost 100% in the absence of timely surveillance). Although typically associated with ten to a few hundred colonic adenomatous polyps that are evident at a mean age of about 50 years, colonic cancer develops in some individuals with biallelic MUTYH pathogenic variants in the absence of polyposis. Duodenal adenomas are found in 17%-25% of individuals with MAP. Serrated adenomas, hyperplastic/sessile serrated polyps, and mixed (hyperplastic and adenomatous) polyps can also occur. The lifetime risk of duodenal cancer is about 4%. Also noted are a modestly increased risk for rather late-onset malignancies of the ovary, bladder, and skin, and some evidence for an increased risk for breast and endometrial cancer. Some affected individuals develop sebaceous gland tumors and more recently, thyroid abnormalities (multinodular goiter, single nodules, and papillary thyroid cancer) have been reported. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK107219]
Heritable Thoracic Aortic Disease Overview
The major cardiovascular manifestations of thoracic aortic aneurysms and aortic dissections (TAAD) include: (1) dilatation of the ascending thoracic aorta at the level of the sinuses of Valsalva or ascending aorta or both; and (2) dissections of the thoracic aorta involving either the ascending (Stanford type A dissections) or descending aorta (Stanford type B). Rarely an aneurysm involving the descending thoracic aorta is observed. Vascular manifestations can be the only findings. In the absence of surgical repair of the ascending aorta, affected individuals typically have progressive enlargement of the ascending aorta leading to an acute aortic dissection. The age of onset and presentation of the aortic disease are highly variable, as are the other vascular diseases and features associated with the aortic disease. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1120]
Glycogen storage disease type V (GSDV, McArdle disease) is a metabolic myopathy characterized by exercise intolerance manifested by rapid fatigue, myalgia, and cramps in exercising muscles. Symptoms usually are precipitated by isometric exercise or sustained aerobic exercise. Most individuals improve their exercise tolerance by exploiting the "second wind" phenomenon with relief of myalgia and fatigue after a few minutes of rest. Age of onset is frequently in the first decade of life but can vary. Fixed muscle weakness occurs in approximately 25% of affected individuals, is more likely to involve proximal muscles, and is more common in individuals of advanced age. Approximately 50% of affected individuals have recurrent episodes of myoglobinuria that could eventually result in acute renal failure, although reported cases are rare. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1344]
Hemophilia A is characterized by deficiency in factor VIII clotting activity that results in prolonged oozing after injuries, tooth extractions, or surgery, and delayed or recurrent bleeding prior to complete wound healing. The age of diagnosis and frequency of bleeding episodes are related to the level of factor VIII clotting activity. In severe hemophilia A, spontaneous joint or deep-muscle bleeding is the most frequent symptom. Individuals with severe hemophilia A are usually diagnosed during the first two years of life; without prophylactic treatment, they may average up to two to five spontaneous bleeding episodes each month. Individuals with moderate hemophilia A seldom have spontaneous bleeding; however, they do have prolonged or delayed oozing after relatively minor trauma and are usually diagnosed before age five to six years; the frequency of bleeding episodes varies, usually from once a month to once a year. Individuals with mild hemophilia A do not have spontaneous bleeding episodes; however, without pre- and postoperative treatment, abnormal bleeding occurs with surgery or tooth extractions; the frequency of bleeding episodes varies widely, typically from once a year to once every ten years. Individuals with mild hemophilia A are often not diagnosed until later in life. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1404]
Barth syndrome is characterized in affected males by cardiomyopathy, neutropenia, skeletal myopathy, prepubertal growth delay, and distinctive facial gestalt (most evident in infancy); not all features may be present in a given patient. Cardiomyopathy, which is almost always present before age five years, is typically dilated cardiomyopathy with or without endocardial fibroelastosis (EFE) or left ventricular noncompaction (LVNC); rarely it is hypertrophic cardiomyopathy (HCM). Heart failure is a significant cause of morbidity and mortality; risk of arrhythmia and sudden death is increased. Neutropenia is most often associated with mouth ulcers, pneumonia, and sepsis. The non-progressive myopathy predominantly affects the proximal muscles, and results in early motor delays. Prepubertal growth delay is followed by a post-pubertal growth spurt with remarkable “catch-up” growth. Heterozygous females who have a normal karyotype are asymptomatic and have normal biochemical studies. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK247162]
PAFAH1B1-Associated Lissencephaly/Subcortical Band Heterotopia
LIS1-associated lissencephaly includes Miller-Dieker syndrome (MDS), isolated lissencephaly sequence (ILS), and (rarely) subcortical band heterotopia (SBH). Lissencephaly and SBH are cortical malformations caused by deficient neuronal migration during embryogenesis. Lissencephaly refers to a "smooth brain" with absent gyri (agyria) or abnormally wide gyri (pachygyria). SBH refers to a band of heterotopic gray matter located just beneath the cortex and separated from it by a thin zone of normal white matter. MDS is characterized by lissencephaly, typical facial features, and severe neurologic abnormalities. ILS is characterized by lissencephaly and its direct sequelae: developmental delay, intellectual disability, and seizures. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK5189]
The disorder hereditary multiple osteochondromas (HMO), previously called hereditary multiple exostoses (HME), is characterized by growths of multiple osteochondromas (benign cartilage-capped bone tumors that grow outward from the metaphyses of long bones). Osteochondromas can be associated with a reduction in skeletal growth, bony deformity, restricted joint motion, shortened stature, premature osteoarthrosis, and compression of peripheral nerves. The median age of diagnosis is three years; nearly all affected individuals are diagnosed by age 12 years. The risk for malignant degeneration to osteochondrosarcoma increases with age, although the lifetime risk of malignant degeneration is low (~1%). [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1235]
Maple syrup urine disease (MSUD) is classified as classic or intermediate. Twelve hours after birth, untreated neonates with classic MSUD have a maple syrup odor in cerumen; by 12-24 hours, elevated plasma concentrations of branched-chain amino acids (BCAAs) (leucine, isoleucine, and valine) and allo-isoleucine, as well as a generalized disturbance of plasma amino acid concentration ratios; by age two to three days, ketonuria, irritability, and poor feeding; by age four to five days, deepening encephalopathy manifesting as lethargy, intermittent apnea, opisthotonus, and stereotyped movements such as "fencing" and "bicycling." By age seven to ten days, coma and central respiratory failure may supervene. Individuals with intermediate MSUD have partial BCKAD enzyme deficiency that only manifests intermittently or responds to dietary thiamine therapy; these individuals can experience severe metabolic intoxication and encephalopathy during sufficient catabolic stress. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1319]
Fryns syndrome is characterized by diaphragmatic defects (diaphragmatic hernia, eventration, hypoplasia or agenesis); characteristic facial appearance (coarse facies, ocular hypertelorism, broad and flat nasal bridge, thick nasal tip, long philtrum, low-set and poorly formed ears, tented upper lip, macrostomia, micrognathia); distal digital hypoplasia (nails, terminal phalanges); pulmonary hypoplasia; and associated anomalies (polyhydramnios, cloudy corneas and/or microphthalmia, orofacial clefting, renal dysplasia/renal cortical cysts, and/or malformations involving the brain, cardiovascular system, gastrointestinal system, genitalia). Survival beyond the neonatal period has been rare. Data on postnatal growth and psychomotor development are limited; however, severe developmental delay and intellectual disability are common. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1459]
Most characteristically, Aicardi-Goutières syndrome (AGS) manifests as an early-onset encephalopathy that usually, but not always, results in severe intellectual and physical handicap. A subgroup of infants with AGS present at birth with abnormal neurologic findings, hepatosplenomegaly, elevated liver enzymes, and thrombocytopenia, a picture highly suggestive of congenital infection. Otherwise, most affected infants present at variable times after the first few weeks of life, frequently after a period of apparently normal development. Typically, they demonstrate the subacute onset of a severe encephalopathy characterized by extreme irritability, intermittent sterile pyrexias, loss of skills, and slowing of head growth. Over time, as many as 40% develop chilblain skin lesions on the fingers, toes, and ears. It is becoming apparent that atypical, sometimes milder, cases of AGS exist, and thus the true extent of the phenotype associated with mutation of the AGS-related genes is not yet known. For example, mutation of ADAR has recently been associated with a clinical presentation of acute bilateral striatal necrosis. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1475]
Hypochondroplasia is a skeletal dysplasia characterized by short stature; stocky build; disproportionately short arms and legs; broad, short hands and feet; mild joint laxity; and macrocephaly. Radiologic features include shortening of long bones with mild metaphyseal flare; narrowing of the inferior lumbar interpedicular distances; short, broad femoral neck; and squared, shortened ilia. The skeletal features are very similar to those seen in achondroplasia but tend to be milder. Medical complications common to achondroplasia (e.g., spinal stenosis, tibial bowing, obstructive apnea) occur less frequently in hypochondroplasia but intellectual disability and epilepsy may be more prevalent. Children usually present as toddlers or school-age children with decreased growth velocity leading to short stature and limb disproportion. Other features also become more prominent over time. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1477]
Focal dermal hypoplasia is a multisystem disorder characterized primarily by involvement of the skin, skeletal system, eyes, and face. Skin manifestations present at birth include atrophic and hypoplastic areas of skin; cutis aplasia; fat nodules in the dermis manifesting as soft, yellow-pink cutaneous nodules; and pigmentary changes. Verrucoid papillomas of the skin and mucous membranes may appear later. The nails can be ridged, dysplastic, or hypoplastic; hair can be sparse or absent. Limb malformations include oligo/syndactyly and split hand/foot. Developmental abnormalities of the eye can include anophthalmia/microphthalmia, iris and chorioretinal coloboma, and lacrimal duct abnormalities. Craniofacial findings can include facial asymmetry, notched alae nasi, cleft lip and palate, and pointed chin. Occasional findings include dental anomalies, abdominal wall defects, diaphragmatic hernia, and renal anomalies. Psychomotor development is usually normal; some individuals have cognitive impairment. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1543]
Neurofibromatosis 2 (NF2) is characterized by bilateral vestibular schwannomas with associated symptoms of tinnitus, hearing loss, and balance dysfunction. The average age of onset is 18 to 24 years. Almost all affected individuals develop bilateral vestibular schwannomas by age 30 years. Affected individuals may also develop schwannomas of other cranial and peripheral nerves, meningiomas, ependymomas, and, very rarely, astrocytomas. Posterior subcapsular lens opacities that rarely progress to a visually significant cataract are the most common ocular findings and may be the first sign of NF2. Mononeuropathy that occurs in childhood is an increasingly recognized finding; it frequently presents as a persistent facial palsy, a squint (third nerve palsy), or hand/foot drop. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1201]
GJB1 Disorders: Charcot Marie Tooth Neuropathy (CMT1X) and Central Nervous System Phenotypes
Charcot-Marie-Tooth neuropathy X type 1 (CMTX1) is characterized by a moderate to severe motor and sensory neuropathy in affected males and usually mild to no symptoms in carrier females. Sensorineural deafness and central nervous system symptoms also occur in some families. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1374]
Achromatopsia is characterized by reduced visual acuity, pendular nystagmus, increased sensitivity to light (photophobia), a small central scotoma, eccentric fixation, and reduced or complete loss of color discrimination. All individuals with achromatopsia (achromats) have impaired color discrimination along all three axes of color vision corresponding to the three cone classes: the protan or long-wavelength-sensitive cone axis (red), the deutan or middle-wavelength-sensitive cone axis (green), and the tritan or short-wavelength-sensitive cone axis (blue). Most individuals have complete achromatopsia, with total lack of function of all three types of cones. Rarely, individuals have incomplete achromatopsia, in which one or more cone types may be partially functioning. The symptoms are similar to those of individuals with complete achromatopsia, but generally less severe. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1418]
SCN9A-related inherited erythromelalgia (SCN9A-related IEM) is characterized by recurrent attacks of bilateral and symmetric intense pain, redness, warmth, and swelling involving the feet and, less frequently, the hands. SCN9A-related IEM is not associated with an organic disease. Manifestations may vary within a family. Onset is usually in childhood or adolescence but has been recognized in infants and adults. At onset, episodes are triggered by warmth; other precipitating factors include: exercise, tight shoes, wearing socks, alcohol, spicy foods, and other vasodilating agents. In advanced disease, symptoms may occur many times a day or become constant. Some individuals have allodynia (pain evoked by a normally innocuous stimulus) and hyperalgesia (increased sensitivity to a painful stimulus). Episodes may be disabling, interfere with sleep, and severely limit normal activities such as walking, participation in sports, wearing socks and shoes, and attending school or going to work. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1163]
Usher syndrome type II is characterized by congenital (i.e., prelingual) bilateral sensorineural hearing loss that is mild to moderate in the low frequencies and severe to profound in the higher frequencies, intact vestibular responses, and retinitis pigmentosa (RP). RP is progressive, bilateral, symmetric retinal degeneration that begins with night blindness and constricted visual fields (tunnel vision) and eventually includes decreased central visual acuity; the rate and degree of vision loss vary within and among families. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1341]
Facioscapulohumeral muscular dystrophy (FSHD) typically presents before age 20 years with weakness of the facial muscles and the stabilizers of the scapula or the dorsiflexors of the foot. Severity is highly variable. Weakness is slowly progressive and approximately 20% of affected individuals eventually require a wheelchair. Life expectancy is not shortened. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1443]
Glycogen storage disease type I (GSDI) is characterized by accumulation of glycogen and fat in the liver and kidneys, resulting in hepatomegaly and renomegaly. The two subtypes (GSDIa and GSDIb) are clinically indistinguishable. Although some untreated neonates present with severe hypoglycemia, more commonly, untreated infants present at age three to four months with hepatomegaly, lactic acidosis, hyperuricemia, hyperlipidemia, hypertriglyceridemia and/or hypoglycemic seizures. Affected children typically have doll-like faces with fat cheeks, relatively thin extremities, short stature, and protuberant abdomen. Xanthoma and diarrhea may be present. Impaired platelet function can lead to a bleeding tendency with frequent epistaxis. Untreated GSDIb is associated with impaired neutrophil and monocyte function as well as chronic neutropenia after the first few years of life, all of which result in recurrent bacterial infections and oral and intestinal mucosal ulcers. Long-term complications of untreated GSDI include growth retardation resulting in short stature, osteoporosis, delayed puberty, gout, renal disease, pulmonary hypertension, hepatic adenomas with potential for malignant transformation, polycystic ovaries, pancreatitis, and changes in brain function. Normal growth and puberty may be expected in treated children. Many affected individuals live into adulthood. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1312]
Pyridoxine-dependent epilepsy is characterized by intractable seizures that are not controlled with antiepileptic drugs but that respond both clinically and electrographically to large daily supplements of pyridoxine (vitamin B6). Multiple types of clinical seizures have been reported in individuals with pyridoxine-dependent epilepsy. Dramatic presentations consisting of prolonged seizures and recurrent episodes of status epilepticus are typical; recurrent self-limited events including partial seizures, generalized seizures, atonic seizures, myoclonic events, and infantile spasms also occur. Affected individuals may have electrographic seizures without clinical correlates. Infants with the classic neonatal presentation begin to experience seizures soon after birth. Atypical features include: late-onset seizures (age ≤3 years); seizures that initially respond to antiepileptic drugs and then become intractable; seizures during early life that do not respond to pyridoxine but that are then controlled with pyridoxine several months later; and prolonged seizure-free intervals (≤5 1/2 months) that occur after pyridoxine discontinuation. Intellectual disability is common. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1486]
Alagille syndrome (ALGS) is a complex multisystem disorder involving primarily the liver, heart, eyes, face, and skeleton. The clinical features are highly variable, even within families. The major clinical manifestations of ALGS are cholestasis, characterized by bile duct paucity on liver biopsy; congenital cardiac defects, primarily involving the pulmonary arteries; posterior embryotoxon in the eye; typical facial features; and butterfly vertebrae. Renal and central nervous abnormalities also occur. Mortality is approximately 10%, with vascular accidents, cardiac disease, and liver disease accounting for most of the deaths. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1273]
COL1A1/2-related osteogenesis imperfecta (OI) is characterized by fractures with minimal or absent trauma, variable dentinogenesis imperfecta (DI), and, in adult years, hearing loss. The clinical features of COL1A1/2-related OI represent a continuum ranging from perinatal lethality to individuals with severe skeletal deformities, mobility impairments, and very short stature to nearly asymptomatic individuals with a mild predisposition to fractures, normal dentition, normal stature, and normal life span. Fractures can occur in any bone, but are most common in the extremities. DI is characterized by grey or brown teeth that may appear translucent and wear down and break easily. COL1A1/2-related OI has been classified into four types (I, II, III, and IV) based on clinical presentation and radiographic findings. This classification system can be helpful in providing information about prognosis and management for a given individual. The four OI types are now referred to as follows:OI type I: classic non-deforming OI with blue sclerae OI type II: perinatally lethal OI OI type III: progressively deforming OI OI type IV: common variable OI with normal sclerae [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1295]
Congenital Central Hypoventilation Syndrome
Congenital central hypoventilation syndrome (CCHS) is a rare disorder of respiratory and autonomic regulation. It is typically characterized by a classic presentation in newborns and, rarely, a milder later-onset (LO-CCHS) presentation in toddlers, children, and adults.Apparent hypoventilation with monotonous respiratory rates and shallow breathing either during sleep only or while awake as well as asleep; Autonomic nervous system dysregulation (ANSD); and In some individuals, altered development of neural crest-derived structures (i.e., Hirschsprung disease) and/or tumors of neural crest origin (neuroblastoma, ganglioneuroma, and ganglioneuroblastoma). [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1427]
Tyrosine hydroxylase (TH) deficiency is associated with a broad phenotypic spectrum. Based on severity of symptoms/signs as well as responsiveness to levodopa therapy, clinical phenotypes caused by TH pathogenic variants are divided into (1) TH-deficient dopa-responsive dystonia (DRD: the mild form of TH deficiency [DYT5b]), (2) TH-deficient infantile parkinsonism with motor delay (the severe form), and (3) TH-deficient progressive infantile encephalopathy (the very severe form).In individuals with TH-deficient DRD, onset is between age 12 months and six years; initial symptoms are typically lower-limb dystonia and/or difficulty in walking. Diurnal fluctuation of symptoms (worsening of the symptoms toward the evening and their alleviation in the morning after sleep) may be present. In most individuals with TH-deficient infantile parkinsonism with motor delay, onset is between age three and 12 months. In contrast to TH-deficient DRD, motor milestones are overtly delayed in this severe form. Affected infants demonstrate truncal hypotonia and parkinsonian symptoms and signs (hypokinesia, rigidity of extremities, and/or tremor). In individuals with TH-deficient progressive infantile encephalopathy, onset is before age three to six months. Fetal distress is reported in most. Affected individuals have marked delay in motor development, truncal hypotonia, severe hypokinesia, limb hypertonia (rigidity and/or spasticity), hyperreflexia, oculogyric crises, ptosis, mental retardation, and paroxysmal periods of lethargy (with increased sweating and drooling) alternating with irritability. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1437]
The spectrum of ATP1A3-related neurologic disorders includes rapid-onset dystonia-parkinsonism (RDP), alternating hemiplegia of childhood (AHC), and cerebellar ataxia, areflexia, pes cavus, optic atrophy, and sensorineural hearing loss (CAPOS) syndrome. While early reports emphasized the distinctness of RDP and AHC, it is increasingly evident that these conditions represent a spectrum related to mutation of ATP1A3. Because only ten individuals from three families and one individual with a de novo mutation have been described with CAPOS syndrome to date, its phenotype is less defined; however, some features overlap with RDP and AHC as well.RDP is characterized by abrupt onset of dystonia with parkinsonism (primarily bradykinesia and postural instability); a clear rostrocaudal (face>arm>leg) topological gradient of involvement; bulbar involvement; and absence of response to an adequate trial of L-dopa therapy. Often fever, physiologic stress, or alcoholic binges trigger the onset of symptoms. After their initial appearance, symptoms often stabilize with little improvement; occasionally second episodes occur with abrupt worsening of symptoms. Anxiety, depression, and seizures have been reported. Age of onset is four to 55 years. AHC is a complex neurodevelopmental syndrome most frequently manifesting in infancy or early childhood with paroxysmal episodic neurologic dysfunction including alternating hemiparesis or dystonia, quadriparesis, seizure-like episodes, and oculomotor abnormalities. Episodes can last for minutes, hours, days, or even weeks. Remission of symptoms occurs with sleep and immediately after awakening. Over time, persistent neurologic deficits develop in the majority of those affected, including oculomotor apraxia, ataxia, choreoathetosis, dystonia, parkinsonism, and cognitive and behavioral dysfunction; more than 50% develop epilepsy in addition to their episodic movement disorder phenotype. CAPOS syndrome (a mnemonic for cerebellar ataxia, areflexia, optic atrophy, and sensorineural hearing loss) is characterized by episodes of ataxic encephalopathy and/or weakness after a febrile illness. Onset is between ages six months and five years. Some acute symptoms resolve; disease progression and severity vary. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1115]
Autosomal dominant multiple epiphyseal dysplasia (MED) presents in early childhood, usually with pain in the hips and/or knees after exercise. Affected children complain of fatigue with long-distance walking. Waddling gait may be present. Adult height is either in the lower range of normal or mildly shortened. The limbs are relatively short in comparison to the trunk. Pain and joint deformity progress, resulting in early-onset osteoarthritis, particularly of the large weight-bearing joints. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1123]
Russell-Silver syndrome (RSS) is characterized by intrauterine growth retardation accompanied by postnatal growth deficiency. The birth weight of affected infants is typically two or more SD below the mean, and postnatal growth two or more SD below the mean for length or height. Affected individuals typically have proportionately short stature, normal head circumference, fifth-finger clinodactyly, typical facial features with triangular facies characterized by broad forehead and narrow chin, and limb-length asymmetry that may result from hemihypotrophy with diminished growth of the affected side. Growth velocity is normal in children with RSS. The average adult height of males is 151.2 cm and that of females is 139.9 cm. Evidence exists that children with RSS are at significant risk for developmental delay (both motor and cognitive) and learning disabilities. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1324]
Glycogen storage disease type II (GSD II), or Pompe disease, is classified by age of onset, organ involvement, severity, and rate of progression. Classic infantile-onset Pompe disease may be apparent in utero but more often presents in the first two months of life with hypotonia, generalized muscle weakness, cardiomegaly and hypertrophic cardiomyopathy, feeding difficulties, failure to thrive, respiratory distress, and hearing loss. Without treatment by enzyme replacement therapy (ERT), classic infantile-onset Pompe disease commonly results in death in the first year of life from progressive left ventricular outflow obstruction. The non-classic variant of infantile-onset Pompe disease usually presents within the first year of life with motor delays and/or slowly progressive muscle weakness, typically resulting in death from ventilatory failure in early childhood. Cardiomegaly can be seen, but heart disease is not a major source of morbidity. Late-onset (i.e., childhood, juvenile, and adult-onset) Pompe disease is characterized by proximal muscle weakness and respiratory insufficiency; clinically significant cardiac involvement is uncommon in the late-onset form. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1261]
Parkin Type of Early-Onset Parkinson Disease
Parkin type of early-onset Parkinson disease is characterized by rigidity, bradykinesia, and resting tremor. Lower-limb dystonia may be a presenting sign. Onset usually occurs between ages 20 and 40 years with an average age of onset in the early to mid-thirties. The disease is slowly progressive and disease duration of more than 50 years has been reported. Clinical signs vary; hyperreflexia is common. Dyskinesia as a result of treatment with levodopa frequently occurs. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1478]
Nephropathic cystinosis in untreated children is characterized by renal tubular Fanconi syndrome, poor growth, hypophosphatemic rickets, impaired glomerular function resulting in complete glomerular failure, and accumulation of cystine crystals in almost all cells, leading to cellular destruction and tissue dysfunction. The typical untreated child has short stature, light complexion, rickets, and photophobia. Failure to thrive is generally noticed after approximately age six months; signs of renal tubular Fanconi syndrome (polyuria, polydipsia, dehydration, and acidosis) appear as early as age six months; corneal crystals can be present before age one year and are always present after age 16 months. Prior to the use of renal transplantation and cystine-depleting therapy, the life span in nephropathic cystinosis was no longer than ten years. With these therapies, affected individuals can survive at least into the mid-forties or fifties with satisfactory quality of life. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1400]
Myotonic dystrophy type 2 (DM2) is characterized by myotonia (90% of affected individuals) and muscle dysfunction (weakness, pain, and stiffness) (82%), and less commonly by cardiac conduction defects, iridescent posterior subcapsular cataracts, insulin-insensitive type 2 diabetes mellitus, and testicular failure. Although myotonia (involuntary muscle contraction with delayed relaxation) has been reported during the first decade, onset is typically in the third decade, most commonly with fluctuating or episodic muscle pain that can be debilitating and weakness of the neck flexors and finger flexors. Subsequently, weakness occurs in the elbow extensors and the hip flexors and extensors. Facial weakness and weakness of the ankle dorsiflexors are less common. Myotonia rarely causes severe symptoms. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1466]
Prolidase deficiency is characterized by skin lesions (typically severe, chronic, recalcitrant, and painful skin ulcers of the lower extremities and telangiectasias of the face and hands), recurrent infections (particularly of the skin and respiratory tract), dysmorphic facial features, variable intellectual disability, and hepatomegaly with elevated liver enzymes and splenomegaly. Anemia, thrombocytopenia, hypergammaglobulinemia, and hypocomplementemia are common. An association between systemic lupus erythematosus (SLE) and prolidase deficiency has been described. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK299584]
Aniridia is characterized by complete or partial iris hypoplasia usually (but not always) with associated foveal hypoplasia resulting in reduced visual acuity and nystagmus presenting in early infancy. Frequently associated ocular abnormalities (often of later onset) include cataract, glaucoma, and corneal opacification and vascularization. Aniridia may occur either as an isolated ocular abnormality without systemic involvement, caused by mutation of PAX6 or deletion of a regulatory region controlling its expression, or as part of the Wilms tumor-aniridia-genital anomalies-retardation (WAGR) syndrome, with a deletion of 11p13 involving the PAX6 (aniridia) locus and the adjacent WT1 (Wilms tumor) locus. Individuals with deletion of PAX6 and WT1 are at up to a 50% risk of developing Wilms tumor. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1360]
Nonsyndromic Retinitis Pigmentosa Overview
Retinitis pigmentosa (RP) is a group of inherited disorders in which abnormalities of the photoreceptors (rods and cones) or the retinal pigment epithelium (RPE) of the retina lead to progressive visual loss. Affected individuals first experience defective dark adaptation or "night blindness," followed by constriction of peripheral visual fields and, eventually, loss of central vision late in the course of the disease. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1417]
Wilson disease is a disorder of copper metabolism that can present with hepatic, neurologic, or psychiatric disturbances, or a combination of these, in individuals ranging from age three years to over 50 years; symptoms vary among and within families. Liver disease includes recurrent jaundice, simple acute self-limited hepatitis-like illness, autoimmune-type hepatitis, fulminant hepatic failure, or chronic liver disease. Neurologic presentations include movement disorders (tremors, poor coordination, loss of fine-motor control, chorea, choreoathetosis) or rigid dystonia (mask-like facies, rigidity, gait disturbance, pseudobulbar involvement). Psychiatric disturbance includes depression, neurotic behaviors, disorganization of personality, and, occasionally, intellectual deterioration. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1512]
Shwachman-Diamond syndrome (SDS) is characterized by exocrine pancreatic dysfunction with malabsorption, malnutrition, and growth failure; hematologic abnormalities with single- or multi-lineage cytopenias and susceptibility to myelodysplasia syndrome (MDS) and acute myelogeneous leukemia (AML); and bone abnormalities. In almost all affected children, persistent or intermittent neutropenia is a common presenting finding, often before the diagnosis of SDS is made. Short stature and recurrent infections are common. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1756]
TFR2-related hereditary hemochromatosis (TFR2-HHC) is characterized by increased intestinal iron absorption resulting in iron accumulation in the liver, heart, pancreas, and endocrine organs. Age of onset is earlier than in HFE-associated HHC. Some individuals present in the second decade and others present as adults with fatigue and arthralgia and/or organ involvement including liver cirrhosis, diabetes mellitus, and arthropathy. In other individuals, TFR2-HHC may not be progressive even if untreated. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1349]
The spectrum of frontotemporal dementia associated with GRN (also known as PGRN) mutation (FTD-GRN or FTD-PGRN) includes the behavioral variant (FTD-bv), primary progressive aphasia (PPA; further sub-categorized as progressive non-fluent aphasia [PNFA] and semantic dementia [SD]), and movement disorders with extrapyramidal features such as parkinsonism and corticobasal syndrome. A broad range of clinical features both within and across families is observed. The age of onset ranges from 35 to 87 years. Behavioral disturbances are the most common early feature, followed by progressive aphasia. Impairment in executive function manifests as loss of judgment and insight. In early stages, PPA often manifests as deficits in naming, word finding, or word comprehension. In late stages, affected individuals often become mute and lose their ability to communicate. Early findings of parkinsonism include rigidity, bradykinesia or akinesia (slowing or absence of movements), limb dystonia, apraxia (loss of ability to carry out learned purposeful movements), and disequilibrium. Late motor findings may include myoclonus, dysarthria, and dysphagia. Most affected individuals eventually lose the ability to walk. Disease duration is three to 12 years. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1371]
Xeroderma pigmentosum (XP) is characterized by:Sun sensitivity (severe sunburn with blistering, persistent erythema on minimal sun exposure in ~60% of affected individuals, and marked freckle-like pigmentation of the face before age 2 years in most affected individuals); Ocular involvement (photophobia, keratitis, atrophy of the skin of the lids); Greatly increased risk of cutaneous neoplasms (basal cell carcinoma, squamous cell carcinoma, melanoma). [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1397]
PIK3CA-associated segmental overgrowth includes disorders of brain (e.g., MCAP [megalencephaly-capillary malformation] syndrome, hemimegalencephaly); and segmental body overgrowth (e.g., CLOVES [congenital lipomatous asymmetric overgrowth of the trunk, lymphatic, capillary, venous, and combined-type vascular malformations, epidermal nevi, skeletal and spinal anomalies] syndrome, fibroadipose hyperplasia [FH]). Heterozygous (usually somatic mosaic) mutations of PIK3CA are causative. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK153722]
Pancreatitis is inflammation of the pancreas that progresses from acute (sudden onset; duration <6 months) to recurrent acute (>1 episode of acute pancreatitis) to chronic (duration >6 months). The range of symptoms and disease course vary from person to person. Familial pancreatitis, defined as pancreatitis from any cause that occurs in a family with an incidence that is greater than would be expected by chance alone, can be non-genetic or genetic, the latter including autosomal dominant hereditary pancreatitis and pancreatitis syndromes characterized by pancreatitis or pancreatic insufficiency. The majority of familial pancreatitis appears to have a complex, multigenic, or gene-environmental etiology with a variable number of germline pathogenic variants in genes that affect trypsin regulation, including CASR, CTRC, and CLDN2. Hereditary pancreatitis (HP) is defined as either two or more individuals with pancreatitis in two or more generations of a family (i.e., an autosomal dominant pattern of inheritance) or pancreatitis associated with a germline PRSS1 disease-causing gain-of-function variant. The phenotype of hereditary pancreatitis is increased susceptibility to acute pancreatitis, with complications such as chronic inflammation, fibrosis, and chronic pain in some affected individuals. Heterozygous pathogenic variants in PRSS1 are found in 60%-100% of families with hereditary pancreatitis, and most large families with pancreatitis spanning multiple generations; biallelic pathogenic variants in SPINK1 or biallelic pathogenic variants in CFTR result in autosomal recessive pancreatitis. Syndromes in which pancreatitis is a finding include: Pearson marrow pancreas syndrome, CEL maturity-onset diabetes of the young (CEL-MODY), and Johanson-Blizzard syndrome. Shwachman-Diamond syndrome, an autosomal recessive disorder, includes pancreatic exocrine insufficiency as well as other features. Idiopathic sporadic pancreatitis is a single occurrence of pancreatitis in a family for which no etiology is identified. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK190101]
Dyskeratosis congenita (DC), a telomere biology disorder, is characterized by a classic triad of dysplastic nails, lacy reticular pigmentation of the upper chest and/or neck, and oral leukoplakia. However, the classic triad may not be present in all individuals. People with DC are at increased risk for progressive bone marrow failure (BMF), myelodysplastic syndrome (MDS) or acute myelogenous leukemia (AML), solid tumors (usually squamous cell carcinoma of the head/neck or anogenital cancer), and pulmonary fibrosis. Other findings can include: abnormal pigmentation changes not restricted to the upper chest and neck, eye abnormalities (epiphora, blepharitis, sparse eyelashes, ectropion, entropion, trichiasis), and dental abnormalities (caries, periodontal disease, taurodauntism). Although most persons with DC have normal psychomotor development and normal neurologic function, significant developmental delay is present in the two variants in which additional findings include cerebellar hypoplasia (Hoyeraal Hreidarsson syndrome) and bilateral exudative retinopathy and intracranial calcifications (Revesz syndrome). Onset and progression of manifestations of DC vary: at the mild end of the spectrum are those who have only minimal physical findings with normal bone marrow function, and at the severe end are those who have the diagnostic triad and early-onset BMF. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK22301]
The phenotypic spectrum of SHOX deficiency disorders, caused by haploinsufficiency of the short stature homeobox-containing gene (SHOX), ranges from Leri-Weill dyschondrosteosis (LWD) at the severe end of the spectrum to nonspecific short stature at the mild end of the spectrum. In adults with SHOX deficiency, the proportion of LWD versus short stature without features of LWD is not well defined. In LWD the classic clinical triad is short stature, mesomelia, and Madelung deformity. Mesomelia, in which the middle portion of a limb is shorted in relation to the proximal portion, can be evident first in school-aged children and increases with age in frequency and severity. Madelung deformity (abnormal alignment of the radius, ulna, and carpal bones at the wrist) typically develops in mid-to-late childhood and is more common and severe in females. The phenotype of short stature caused by SHOX deficiency (in the absence of mesomelia and Madelung deformity) is highly variable, even within the same family. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1215]
Usher syndrome type I is characterized by congenital, bilateral, profound sensorineural hearing loss, vestibular areflexia, and adolescent-onset retinitis pigmentosa. Unless fitted with a cochlear implant, individuals do not typically develop speech. Retinitis pigmentosa (RP), a progressive, bilateral, symmetric degeneration of rod and cone functions of the retina, develops in adolescence, resulting in progressively constricted visual fields and impaired visual acuity. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1265]
Androgen insensitivity syndrome (AIS) is typically characterized by evidence of feminization (i.e., undermasculinization) of the external genitalia at birth, abnormal secondary sexual development in puberty, and infertility in individuals with a 46,XY karyotype. AIS represents a spectrum of defects in androgen action and can be subdivided into three broad phenotypes: Complete androgen insensitivity syndrome (CAIS), with typical female external genitalia Partial androgen insensitivity syndrome (PAIS) with predominantly female, predominantly male, or ambiguous external genitalia Mild androgen insensitivity syndrome (MAIS) with typical male external genitalia [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1429]
PMM2-CDG (CDG-Ia) (previously known as congenital disorder of glycosylation type 1a), the most common of a group of disorders of abnormal glycosylation of N-linked oligosaccharides, is divided into three types: infantile multisystem, late-infantile and childhood ataxia-intellectual disability, and adult stable disability. The three types notwithstanding, clinical presentation and course are highly variable, ranging from infants who die in the first year of life to mildly involved adults. Clinical presentations tend to be similar in siblings.In the infantile multisystem type, infants show axial hypotonia, hyporeflexia, esotropia, and developmental delay. Feeding problems, vomiting, failure to thrive, and impaired growth are frequently seen. Subcutaneous fat may be excessive over the buttocks and suprapubic region. Two distinct clinical presentations are observed: (1) a non-fatal neurologic form with strabismus, psychomotor retardation, and cerebellar hypoplasia in infancy followed by neuropathy and retinitis pigmentosa in the first or second decade and (2) a neurologic-multivisceral form with approximately 20% mortality in the first year of life. The late-infantile and childhood ataxia-intellectual disability type, with onset between age three and ten years, is characterized by hypotonia, ataxia, severely delayed language and motor development, inability to walk, and IQ of 40 to 70; other findings include seizures, stroke-like episodes or transient unilateral loss of function, retinitis pigmentosa, joint contractures, and skeletal deformities. In the adult stable disability type, intellectual ability is stable; peripheral neuropathy is variable, thoracic and spinal deformities progress, and premature aging is observed; females lack secondary sexual development and males may exhibit decreased testicular volume. Hyperglycemia-induced growth hormone release, hyperprolactinemia, insulin resistance, and coagulopathy may occur. An increased risk for deep venous thrombosis is present. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1110]
Citrin deficiency can manifest in newborns as neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD), in older children as failure to thrive and dyslipidemia caused by citrin deficiency (FTTDCD), and in adults as recurrent hyperammonemia with neuropsychiatric symptoms in citrullinemia type II (CTLN2). Often citrin deficiency is characterized by fondness for protein-rich and/or lipid-rich foods and aversion to carbohydrate-rich foods. tabaNICCD. Children younger than age one year have growth retardation with transient intrahepatic cholestasis, hepatomegaly, diffuse fatty liver, and parenchymal cellular infiltration associated with hepatic fibrosis, variable liver dysfunction, hypoproteinemia, decreased coagulation factors, hemolytic anemia, and/or hypoglycemia. Although NICCD is generally not severe and symptoms often resolve by age one year with appropriate treatment, some infants succumb to infection and liver cirrhosis and others require liver transplantation. FTTDCD. Around age one to two years, many children with citrin deficiency develop the food preferences mentioned. Some have growth retardation, hypoglycemia, and fatigue as well as hyperlipidemia, pancreatitis, fatty liver, and hepatoma. One or more decades later, some individuals with NICCD or FTTDCD develop CTLN2. CTLN2. Onset is sudden and usually between ages 11 and 79 years. Manifestations are recurrent hyperammonemia with neuropsychiatric symptoms including nocturnal delirium, aggression, irritability, hyperactivity, delusions, disorientation, restlessness, drowsiness, loss of memory, flapping tremor, convulsive seizures, and coma; death can result from brain edema. Symptoms are often provoked by alcohol and sugar intake, medication, and/or surgery. Affected individuals may or may not have a prior history of NICCD or FTTDCD. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1181]
Cerebrotendinous xanthomatosis (CTX) is a lipid storage disease characterized by infantile-onset diarrhea, childhood-onset cataract, adolescent- to young adult-onset tendon xanthomas, and adult-onset progressive neurologic dysfunction (dementia, psychiatric disturbances, pyramidal and/or cerebellar signs, dystonia, atypical parkinsonism, peripheral neuropathy, and seizures). Chronic diarrhea from infancy may be the earliest clinical manifestation. In approximately 75% of affected individuals, cataracts are the first finding, often appearing in the first decade of life. Xanthomas appear in the second or third decade; they occur on the Achilles tendon, the extensor tendons of the elbow and hand, the patellar tendon, and the neck tendons. Xanthomas have been reported in the lung, bones, and central nervous system. Some individuals show mental impairment from early infancy, whereas the majority have normal or only slightly subnormal intellectual function until puberty; dementia with slow deterioration in intellectual abilities occurs in the 20s in more than 50% of individuals. Neuropsychiatric symptoms such as behavioral changes, hallucinations, agitation, aggression, depression, and suicide attempts may be prominent. Pyramidal signs (i.e., spasticity) and/or cerebellar signs almost invariably become evident between ages 20 and 30 years. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1409]
Generalized Arterial Calcification of Infancy
Generalized arterial calcification of infancy (GACI) is characterized by infantile onset of widespread arterial calcification and/or narrowing of large- and medium-sized vessels resulting in cardiovascular findings (which can include heart failure, respiratory distress, edema, cyanosis, hypertension, and/or cardiomegaly). Additional findings can include extravascular calcifications (particularly periarticular), typical skin and retinal manifestations of pseudoxanthoma elasticum (PXE), hearing loss, and development of rickets after infancy. While mortality in infancy is high, survival into the second and third decade has been reported. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK253403]
von Willebrand disease (VWD), a congenital bleeding disorder caused by deficient or defective plasma von Willebrand factor (VWF), may only become apparent on hemostatic challenge, and bleeding history may become more apparent with increasing age. Type 2A, which usually manifests as mild to moderate mucocutaneous bleeding; Type 2B, which typically manifests as mild to moderate mucocutaneous bleeding that can include thrombocytopenia that worsens in certain circumstances; Type 2M, which typically manifests as mild-moderate mucocutaneous bleeding; Type 2N, which can manifest as excessive bleeding with surgery and mimics mild hemophilia A. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK7014]
Spastic paraplegia 4 (SPG4; also known as SPAST-associated HSP) is characterized by insidiously progressive bilateral lower-limb gait spasticity. More than 50% of affected individuals have some weakness in the legs and impaired vibration sense at the ankles. About one third have sphincter disturbances. Onset is insidious, mostly in young adulthood, although symptoms may start as early as age one year and as late as age 76 years. Intrafamilial variation is considerable. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1160]
NDP-related retinopathies are characterized by a spectrum of fibrous and vascular changes of the retina at birth that progress through childhood or adolescence to cause varying degrees of visual impairment. The most severe phenotype is described as Norrie disease (ND), characterized by greyish yellow fibrovascular masses (pseudogliomas) secondary to retinal vascular dysgenesis and detachment. Congenital blindness is almost always present. Approximately 30%-50% of males with ND have developmental delay/intellectual disability, behavioral abnormalities, or psychotic-like features. The majority of males with ND develop sensorineural hearing loss. Less severe phenotypes include: persistent hyperplastic primary vitreous (PHPV), characterized by a fibrotic white stalk from the optic disk to the lens; X-linked familial exudative vitreoretinopathy (XL-FEVR), characterized by peripheral retinal vascular anomalies with or without fibrotic changes and retinal detachment; retinopathy of prematurity (ROP); and Coats disease, an exudative proliferative vasculopathy. Phenotypes can vary within families. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1331]
Dense deposit disease (DDD)/membranoproliferative glomerulonephritis type II (MPGNII) is characterized by onset of hematuria and/or proteinuria, acute nephritic syndrome, or nephrotic syndrome. It most frequently affects children between ages five and 15 years. Spontaneous remissions are uncommon and about 50% of affected individuals develop end-stage renal disease (ESRD) within ten years of diagnosis. DDD/MPGNII can be associated with acquired partial lipodystrophy (APL). Drusen, whitish-yellow deposits within Bruch's membrane of the retina often develop in the second decade of life; they initially have little impact on vision, but cause vision problems from subretinal neovascular membranes, macular detachment, and central serous retinopathy in about 10% of affected individuals. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1425]
Chronic granulomatous disease (CGD) is a primary immunodeficiency disorder of phagocytes (neutrophils, monocytes, macrophages, and eosinophils) resulting from impaired killing of bacteria and fungi. CGD is characterized by severe recurrent bacterial and fungal infections and dysregulated inflammatory response resulting in granuloma formation and other inflammatory disorders such as colitis. Infections typically involve the lung (pneumonia), lymph nodes (lymphadenitis), liver (abscess), bone (osteomyelitis), and skin (abscesses or cellulitis); granulomas typically involve the genitourinary system (bladder) and gastrointestinal track (often the pylorus initially, and later the esophagus, jejunum, ileum, cecum, rectum, and perirectal area). Some males with X-linked CGD have McLeod neuroacanthocytosis syndrome as the result of a contiguous gene deletion. CGD may present any time from infancy to late adulthood; however, the vast majority of affected individuals are diagnosed before age five years. Use of antimicrobial prophylaxis and therapy has greatly improved overall survival. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK99496]
Primary ciliary dyskinesia (PCD) is associated with situs abnormalities, abnormal sperm motility, and abnormal ciliary structure and function that result in retention of mucus and bacteria in the respiratory tract leading to chronic otosinopulmonary disease. More than 75% of full-term neonates with PCD have ‘neonatal respiratory distress’ requiring supplemental oxygen for days to weeks. Chronic airway infection, apparent in early childhood, results in bronchiectasis that is almost uniformly present in adulthood. Nasal congestion and sinus infections, apparent in early childhood, persist through adulthood. Chronic/recurrent ear infection, apparent in most young children, can be associated with transient or later irreversible hearing loss. Situs inversus totalis (mirror-image reversal of all visceral organs with no apparent physiologic consequences) is present in 40%-50% of individuals with PCD; heterotaxy (discordance of right and left patterns of ordinarily asymmetric structures that can be associated with significant malformations) is present in approximately 12%. Virtually all males with PCD are infertile as a result of abnormal sperm motility. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1122]
Alzheimer disease (AD) is characterized by dementia that typically begins with subtle and poorly recognized failure of memory and slowly becomes more severe and, eventually, incapacitating. Other common findings include confusion, poor judgment, language disturbance, agitation, withdrawal, and hallucinations. Occasionally, seizures, Parkinsonian features, increased muscle tone, myoclonus, incontinence, and mutism occur. Death usually results from general inanition, malnutrition, and pneumonia. The typical clinical duration of the disease is eight to ten years, with a range from one to 25 years. Approximately 25% of all AD is familial (i.e., ≥2 persons in a family have AD) of which approximately 95% is late onset (age >60-65 years) and 5% is early onset (age <65 years). [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1161]
Niemann-Pick disease type C (NPC) is a lipid storage disease that can present in infants, children, or adults. Neonates can present with ascites and severe liver disease from infiltration of the liver and/or respiratory failure from infiltration of the lungs. Other infants, without liver or pulmonary disease, have hypotonia and developmental delay. The classic presentation occurs in mid-to-late childhood with the insidious onset of ataxia, vertical supranuclear gaze palsy (VSGP), and dementia. Dystonia and seizures are common. Dysarthria and dysphagia eventually become disabling, making oral feeding impossible; death usually occurs in the late second or third decade from aspiration pneumonia. Adults are more likely to present with dementia or psychiatric symptoms. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1296]
Beta-thalassemia (β-thalassemia) is characterized by reduced synthesis of the hemoglobin subunit beta (hemoglobin beta chain) that results in microcytic hypochromic anemia, an abnormal peripheral blood smear with nucleated red blood cells, and reduced amounts of hemoglobin A (HbA) on hemoglobin analysis. Individuals with thalassemia major have severe anemia and hepatosplenomegaly; they usually come to medical attention within the first two years of life. Without treatment, affected children have severe failure to thrive and shortened life expectancy. Treatment with a regular transfusion program and chelation therapy, aimed at reducing transfusion iron overload, allows for normal growth and development and may improve the overall prognosis. Individuals with thalassemia intermedia present later and have milder anemia that only rarely requires transfusion. These individuals are at risk for iron overload secondary to increased intestinal absorption of iron as a result of ineffective erythropoiesis. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1426]
Hemophagocytic Lymphohistiocytosis, Familial
Familial hemophagocytic lymphohistiocytosis (FHL) is characterized by proliferation and infiltration of hyperactivated macrophages and T-lymphocytes manifesting as acute illness with prolonged fever, cytopenias, and hepatosplenomegaly. Onset is typically within the first months or years of life and, on occasion, in utero, although later childhood or adult onset is more common than previously suspected. Neurologic abnormalities may be present initially or may develop later; they may include increased intracranial pressure, irritability, neck stiffness, hypotonia, hypertonia, convulsions, cranial nerve palsies, ataxia, hemiplegia, quadriplegia, blindness, and coma. Rash and lymphadenopathy are less common. Other findings include liver dysfunction and bone marrow hemophagocytosis. The median survival of children with typical FHL, without treatment, is less than two months; progression of hemophagocytic lymphohistiocytosis and infection account for the majority of deaths in untreated individuals. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1444]
Congenital myasthenic syndromes (designated as CMS throughout this entry) are characterized by fatigable weakness of skeletal muscle (e.g., ocular, bulbar, limb muscles) with onset at or shortly after birth or in early childhood; rarely, symptoms may not manifest until later in childhood. Cardiac and smooth muscle are not involved. Severity and course of disease are highly variable, ranging from minor symptoms to progressive disabling weakness. In some subtypes of CMS, myasthenic symptoms may be mild, but sudden severe exacerbations of weakness or even sudden episodes of respiratory insufficiency may be precipitated by fever, infections, or excitement. Major findings of the neonatal onset subtype include: feeding difficulties; poor suck and cry; choking spells; eyelid ptosis; facial, bulbar, and generalized weakness. In addition arthrogryposis multiplex congenital may be present; respiratory insufficiency with sudden apnea and cyanosis may occur. Later childhood onset subtypes show abnormal muscle fatigability with difficulty in activities such as running or climbing stairs; motor milestones may be delayed; fluctuating eyelid ptosis and fixed or fluctuating extraocular muscle weakness are common presentations. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1168]
Isolated Gonadotropin-Releasing Hormone (GnRH) Deficiency
Isolated gonadotropin-releasing hormone (GnRH) deficiency (IGD) is characterized by inappropriately low serum concentrations of the gonadotropins LH (luteinizing hormone) and FSH (follicle-stimulating hormone) in the setting of hypogonadism. IGD is associated with a normal sense of smell (normosmic IGD) in approximately 40% of affected individuals and an impaired sense of smell (Kallmann syndrome [KS]) in approximately 60%. IGD can first be apparent in infancy, adolescence, or adulthood. Infant boys with congenital (i.e., present at birth) IGD often have micropenis and cryptorchidism. Adolescents and adults with IGD have clinical evidence of hypogonadism and incomplete sexual maturation on physical examination. Adult males with IGD tend to have prepubertal testicular volume (i.e., <4 mL), absence of secondary sexual features (e.g., facial and axillary hair growth, deepening of the voice), decreased muscle mass, diminished libido, erectile dysfunction, and infertility. Adult females have little or no breast development and primary amenorrhea. Although skeletal maturation is delayed, the rate of linear growth is usually normal except for the absence of a distinct pubertal growth spurt. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1334]
Hypokalemic periodic paralysis (HOKPP) is a condition in which affected individuals may experience paralytic episodes with concomitant hypokalemia (<2.5 mmol/L), and occasionally may develop late-onset proximal myopathy. The paralytic attacks are characterized by reversible flaccid paralysis usually leading to paraparesis or tetraparesis but typically sparing the respiratory muscles and heart. Acute paralytic crises usually last at least several hours and sometimes days. Some individuals have only one episode in a lifetime; more commonly, crises occur repeatedly: daily, weekly, monthly, or less often. The major triggering factors are carbohydrate-rich meals and rest after exercise; rarely, cold-induced hypokalemic paralysis has been reported. The interval between crises may vary and may be prolonged by preventive treatment with potassium salts or acetazolamide. The age of onset of the first attack ranges from one to 20 years; the frequency of attacks is highest between ages 15 and 35 and then decreases with age. A variable myopathy develops in at least 25% of affected individuals and may result in a progressive fixed muscle weakness that manifests at variable ages as exercise intolerance predominantly in the lower limbs. It may occur independent of paralytic symptoms and may be the sole manifestation of HOKPP. Individuals with HOKPP are at increased risk for pre- or post-anesthetic weakness and may be at an increased risk for malignant hyperthermia – though not as great a risk as in individuals with true autosomal dominant malignant hyperthermia susceptibility (MHS). [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1338]
X-linked centronuclear myopathy (XLCNM) (also known as myotubular myopathy [MTM]) is characterized by muscle weakness that ranges from severe to mild. Severe (classic) XLCNM presents prenatally with polyhydramnios and decreased fetal movement and in newborns with weakness, hypotonia, and respiratory distress. Affected males have significantly delayed motor milestones and most fail to achieve independent ambulation. Weakness is profound and often involves facial and extraocular muscles. Respiratory failure is nearly uniform, with most affected individuals requiring 24-hour ventilatory assistance. A minority of males with severe XLCNM die in infancy. Males with moderate XLCNM achieve motor milestones more quickly than males with the severe form; about 40% require no ventilator support or intermittent support. Males with mild XLCNM may require ventilatory support only in the newborn period; they have minimally delayed motor milestones, are able to walk, and may lack myopathic facies. The muscle disease of XLCNM is not obviously progressive. Female carriers of XLCNM are generally asymptomatic, although rare manifesting heterozygotes have been described. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1432]
Classic Cornelia de Lange syndrome (CdLS) is characterized by distinctive facial features, growth retardation (prenatal onset; <5th centile throughout life), hirsutism, and upper limb reduction defects that range from subtle phalangeal abnormalities to oligodactyly (missing digits). Craniofacial features include synophrys, arched eyebrows, long eyelashes, small upturned nose, small widely spaced teeth, and microcephaly. IQ ranges from below 30 to 102 (mean: 53). Many individuals demonstrate autistic and self-destructive tendencies. Frequent findings include cardiac septal defects, gastrointestinal dysfunction, hearing loss, myopia, and cryptorchidism or hypoplastic genitalia. Individuals with a milder phenotype have less severe growth, cognitive, and limb involvement, but often have facial features consistent with CdLS. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1104]
Achondroplasia is the most common process resulting in disproportionate small stature. Affected individuals have short arms and legs, a large head, and characteristic facial features with frontal bossing and midface retrusion (formerly known as midface hypoplasia). In infancy, hypotonia is typical, and acquisition of developmental motor milestones is often both aberrant in pattern and delayed. Intelligence and life span are usually near normal, although craniocervical junction compression increases the risk of death in infancy. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1152]
Spinocerebellar ataxia type 1 (SCA1) is characterized by progressive cerebellar ataxia, dysarthria, and eventual deterioration of bulbar functions. Early in the disease, affected individuals may have gait disturbance, slurred speech, difficulty with balance, brisk deep tendon reflexes, hypermetric saccades, nystagmus, and mild dysphagia. Later signs include slowing of saccadic velocity, development of up-gaze palsy, dysmetria, dysdiadochokinesia, and hypotonia. In advanced stages, muscle atrophy, decreased deep tendon reflexes, loss of proprioception, cognitive impairment (e.g., frontal executive dysfunction, impaired verbal memory), chorea, dystonia, and bulbar dysfunction are seen. Onset is typically in the third or fourth decade, although childhood onset and late adult onset have been reported. Those with onset over age 60 years may manifest a pure cerebellar phenotype. Interval from onset to death varies from ten to 30 years; individuals with juvenile onset show more rapid progression and more severe disease. Anticipation is observed. An axonal sensory neuropathy detected by electrophysiologic testing is common; brain imaging typically shows cerebellar and brain stem atrophy. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1184]
Cystic Fibrosis and Congenital Absence of the Vas Deferens
CFTR-related disorders include cystic fibrosis (CF) and congenital absence of the vas deferens (CAVD). Cystic fibrosis affects epithelia of the respiratory tract, exocrine pancreas, intestine, male genital tract, hepatobiliary system, and exocrine sweat glands, resulting in complex multisystem disease. Pulmonary disease is the major cause of morbidity and mortality in CF. Affected individuals have lower airway inflammation and chronic endobronchial infection, progressing to end-stage lung disease characterized by extensive airway damage (bronchiectasis, cysts, and abscesses) and fibrosis of lung parenchyma. Meconium ileus occurs at birth in 15%-20% of newborns with CF. Pancreatic insufficiency with malabsorption occurs in the great majority of individuals with CF. More than 95% of males with CF are infertile as a result of azoospermia caused by absent, atrophic, or fibrotic Wolffian duct structures. CAVD occurs in men without pulmonary or gastrointestinal manifestations of CF. Affected men have azoospermia and are thus infertile. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1250]
Li-Fraumeni syndrome (LFS) is a cancer predisposition syndrome associated with the development of the following classic tumors: soft tissue sarcoma, osteosarcoma, pre-menopausal breast cancer, brain tumors, adrenocortical carcinoma (ACC), and leukemias. In addition, a variety of other neoplasms may occur. LFS-related cancers often occur in childhood or young adulthood and survivors have an increased risk for multiple primary cancers. Age-specific cancer risks have been calculated. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1311]
Beckwith-Wiedemann syndrome (BWS) is a growth disorder characterized by macrosomia, macroglossia, visceromegaly, embryonal tumors (e.g., Wilms tumor, hepatoblastoma, neuroblastoma, and rhabdomyosarcoma), omphalocele, neonatal hypoglycemia, ear creases/pits, adrenocortical cytomegaly, and renal abnormalities (e.g., medullary dysplasia, nephrocalcinosis, medullary sponge kidney, and nephromegaly). Early death may occur from complications of prematurity, hypoglycemia, cardiomyopathy, macroglossia, or tumors. However, the previously reported mortality of 20% is likely an overestimate given better recognition of the disorder along with enhanced treatment options. Macroglossia and macrosomia are generally present at birth but may have postnatal onset. Growth rate slows around age seven to eight years. Hemihyperplasia may affect segmental regions of the body or selected organs and tissues. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1394]
Dystrophic epidermolysis bullosa (DEB) comprises two types based on inheritance pattern:Recessive DEB, including severe generalized (RDEB-sev gen; formerly called Hallopeau-Siemens type [RDEB-HS]) and generalized other (RDEB-O; formerly called non-Hallopeau-Siemens type [RDEB-non-HS]) Dominant DEB (DDEB) [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1304]
Muenke syndrome is defined by the presence of the specific FGFR3 pathogenic variant, c.749C>G, that results in the protein change p.Pro250Arg. Muenke syndrome is characterized by considerable phenotypic variability: features may include coronal synostosis (more often bilateral than unilateral); synostosis of other sutures, all sutures (pan synostosis), or no sutures; or macrocephaly. Bilateral coronal synostosis typically results in brachycephaly (reduced anteroposterior dimenstion of the skull), although turribrachycephaly (a "tower-shaped" skull) or a cloverleaf skull can be observed. Unilateral coronal synostosis results in anterior plagiocephaly (asymmetry of the skull and face). Other craniofacial findings typically include: temporal bossing; widely spaced eyes, ptosis or proptosis (usually mild); midface retrusion; and highly arched palate or cleft lip and palate. Strabismus is common. Other findings can include: hearing loss (in 33%-100% of affected individuals); developmental delay (~33%); epilepsy; intracranial anomalies; intellectual disability; carpal bone and/or tarsal bone fusions; brachydactyly, broad toes, broad thumbs, and/or clinodactyly; and radiographic findings of thimble-like (short and broad) middle phalanges and/or cone-shaped epiphyses. Phenotypic variability is considerable even within the same family. Of note, some individuals who have the p.Pro250Arg pathogenic variant may have no signs of Muenke syndrome on physical or radiographic examination. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1415]
Autosomal Dominant Epilepsy with Auditory Features
Autosomal dominant partial epilepsy with auditory features (ADPEAF) is an idiopathic focal epilepsy syndrome with auditory symptoms and/or receptive aphasia as prominent ictal manifestations. The most common auditory symptoms are simple unformed sounds including humming, buzzing, or ringing; less common forms are distortions (e.g., volume changes) or complex sounds (e.g., specific songs or voices). Ictal receptive aphasia consists of a sudden onset of inability to understand language in the absence of general confusion. Less commonly, other ictal symptoms may occur, including sensory symptoms (visual, olfactory, vertiginous, or cephalic), or motor, psychic, and autonomic symptoms. Most affected individuals have secondarily generalized seizures, usually accompanied by simple partial and complex partial seizures, with auditory symptoms as a major simple partial seizure manifestation. Some persons have seizures precipitated by sounds such as a ringing telephone. Age at onset ranges from four to 50 years but is usually in adolescence or early adulthood. The clinical course of ADPEAF is benign. Seizures are usually well controlled after initiation of medical therapy. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1537]
POLG-related disorders comprise a continuum of overlapping phenotypes that were clinically defined long before their molecular basis was known. These phenotypes exemplify the diversity that can result from mutation of a given gene. Most affected individuals have some, but not all, of the features of a given phenotype; nonetheless, the following nomenclature can assist the clinician in diagnosis and management. Onset of the POLG-related disorders ranges from infancy to late adulthood.Alpers-Huttenlocher syndrome (AHS), one of the most severe phenotypes, is characterized by childhood-onset progressive and ultimately severe encephalopathy with intractable epilepsy and hepatic failure. Childhood myocerebrohepatopathy spectrum (MCHS) presents between the first few months of life up to about age three years with developmental delay or dementia, lactic acidosis, and a myopathy with failure to thrive. Other findings can include liver failure, renal tubular acidosis, pancreatitis, cyclic vomiting, and hearing loss. Myoclonic epilepsy myopathy sensory ataxia (MEMSA) now describes the spectrum of disorders with epilepsy, myopathy, and ataxia without ophthalmoplegia. MEMSA now includes the disorders previously described as spinocerebellar ataxia with epilepsy (SCAE). The ataxia neuropathy spectrum (ANS) includes the phenotypes previously referred to as mitochondrial recessive ataxia syndrome (MIRAS) and sensory ataxia neuropathy dysarthria and ophthalmoplegia (SANDO). About 90% of persons in the ANS have ataxia and neuropathy as core features. Approximately two thirds develop seizures and almost one half develop ophthalmoplegia; clinical myopathy is rare. Autosomal recessive progressive external ophthalmoplegia (arPEO) is characterized by progressive weakness of the extraocular eye muscles resulting in ptosis and ophthalmoparesis (or paresis of the extraocular muscles) without associated systemic involvement; however, caution is advised because many individuals with apparently isolated arPEO at the onset develop other manifestations of POLG-related disorders over years or decades. Of note, in the ANS spectrum the neuropathy commonly precedes the onset of PEO by years to decades. Autosomal dominant progressive external ophthalmoplegia (adPEO) typically includes a generalized myopathy and often variable degrees of sensorineural hearing loss, axonal neuropathy, ataxia, depression, Parkinsonism, hypogonadism, and cataracts (in what has been called “chronic progressive external ophthalmoplegia plus,” or “CPEO+”). [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK26471]
Leber hereditary optic neuropathy (LHON) is characterized by bilateral, painless, subacute visual failure that develops during young adult life. Males are four to five times more likely than females to be affected. Affected individuals are usually entirely asymptomatic until they develop visual blurring affecting the central visual field in one eye; similar symptoms appear in the other eye an average of two to three months later. In about 25% of cases, visual loss is bilateral at onset. Visual acuity is severely reduced to counting fingers or worse in the majority of cases, and visual field testing shows an enlarging dense central or centrocecal scotoma. After the acute phase, the optic discs become atrophic. Significant improvements in visual acuity are rare and most persons qualify for registration as legally blind (visual acuity ≤20/200). Neurologic abnormalities such as postural tremor, peripheral neuropathy, nonspecific myopathy, and movement disorders have been reported to be more common in individuals with LHON than in controls. Some individuals with LHON, usually women, may also develop a multiple sclerosis (MS)-like illness. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1174]
Familial Cerebral Cavernous Malformation
Cerebral cavernous malformations (CCMs) are vascular malformations in the brain and spinal cord comprising closely clustered, enlarged capillary channels (caverns) with a single layer of endothelium without mature vessel wall elements or normal intervening brain parenchyma. The diameter of CCMs ranges from a few millimeters to several centimeters. CCMs increase or decrease in size and increase in number over time. Hundreds of lesions may be identified, depending on the person’s age and the quality and type of brain imaging used. Although CCMs have been reported in infants and children, the majority become evident between the second and fifth decades with findings such as seizures, focal neurologic deficits, nonspecific headaches, and cerebral hemorrhage. Up to 50% of individuals with CCM remain symptom free throughout their lives. Familial cerebral cavernous malformation (FCCM) is defined as the occurrence of CCMs in at least two family members and/or the presence of multiple CCMs and/or the presence of a disease-causing mutation in one of the three genes in which mutations are known to cause familial CCM. Cutaneous vascular lesions are found in 9% of those with FCCM and retinal vascular lesions in almost 5%. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1293]
Alpha-1 antitrypsin deficiency (AATD) is characterized by an increased risk for: chronic obstructive pulmonary disease (i.e., emphysema, persistent airflow obstruction, and/or chronic bronchitis) in adults; liver disease in children and adults; panniculitis ; and c-ANCA positive vasculitis. Emphysema, sometimes with associated bronchiectasis, is the most common manifestation of AATD. Smoking is the major factor influencing the course of chronic obstructive pulmonary disease (COPD). The onset of respiratory disease in smokers with AATD is characteristically between ages 40 and 50 years; in non-smokers, the onset can be delayed to the sixth decade, and some non-smokers never develop COPD. Non-smokers may have a normal life span. Although reported, emphysema in children with AATD is extremely rare. AATD-associated liver disease, which is present in only a small portion of affected children, manifests as obstructive jaundice and increased serum aminotransferase levels in the early days and months of life. The incidence of liver disease increases with age. Liver disease in adults (manifesting as cirrhosis and fibrosis) may occur in the absence of a history of neonatal or childhood liver disease. The risk for hepatocellular carcinoma (HCC) is increased in individuals with AATD. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1519]
PLP1-related disorders of central nervous system myelin formation include a range of phenotypes from Pelizaeus-Merzbacher disease (PMD) to spastic paraplegia 2 (SPG2). PMD typically manifests in infancy or early childhood with nystagmus, hypotonia, and cognitive impairment; the findings progress to severe spasticity and ataxia. Life span is shortened. SPG2 manifests as spastic paraparesis with or without CNS involvement and usually normal life span. Intrafamilial variation of phenotypes can be observed, but the signs are usually fairly consistent within families. Female carriers may manifest mild to moderate signs of the disease. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1182]
Progressive Myoclonus Epilepsy, Lafora Type
Lafora disease (LD) is characterized by fragmentary, symmetric, or generalized myoclonus and/or generalized tonic-clonic seizures, visual hallucinations (occipital seizures), and progressive neurologic degeneration including cognitive and/or behavioral deterioration, dysarthria, and ataxia beginning in previously healthy adolescents between ages 12 and 17 years. The frequency and intractability of seizures increase over time. Status epilepticus is common. Emotional disturbance and confusion are common at or soon after onset of seizures and are followed by dementia. Dysarthria and ataxia appear early, spasticity late. Most affected individuals die within ten years of onset, usually from status epilepticus or from complications related to nervous system degeneration. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1389]
Disorders of Intracellular Cobalamin Metabolism
The clinical manifestations of disorders of intracellular cobalamin metabolism can be highly variable even within a single complementation group. The prototype and best understood is cblC; it is also the most common of these disorders. The age of initial presentation of cblC spans a wide range, including:Newborns, who can have intrauterine growth retardation (IUGR) and microcephaly; Infants, who can have poor feeding, failure to thrive, pallor, and neurologic signs, and occasionally hemolytic uremic syndrome (HUS) and/or seizures including infantile spasms; Toddlers, who can have failure to thrive, poor head growth, cytopenias (including megaloblastic anemia), global developmental delay, encephalopathy, and neurologic signs such as hypotonia and seizures; and Adolescents and adults, who can have neuropsychiatric symptoms, progressive cognitive decline, and/or subacute combined degeneration of the spinal cord. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1328]
Nonsyndromic permanent neonatal diabetes mellitus (PNDM) is characterized by the onset of hyperglycemia within the first six months of life (mean age: 7 weeks; range: birth to 26 weeks) that does not resolve over time. Clinical manifestations at the time of diagnosis include intrauterine growth retardation (IUGR), hyperglycemia, glycosuria, osmotic polyuria, severe dehydration, and failure to thrive. Therapy with insulin corrects the hyperglycemia and allows for catch-up growth. The course of PNDM varies by genotype. Pancreatic agenesis/hypoplasia caused by homozygous pathogenic variants in PDX1 results in severe insulin deficiency and exocrine pancreatic insufficiency. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1447]
Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease involving both upper motor neurons (UMN) and lower motor neurons (LMN). UMN signs include hyperreflexia, extensor plantar response, increased muscle tone, and weakness in a topographic representation. LMN signs include weakness, muscle wasting, hyporeflexia, muscle cramps, and fasciculations. Initial presentation varies. Affected individuals typically present with either asymmetric focal weakness of the extremities (stumbling or poor handgrip) or bulbar findings (dysarthria, dysphagia). Other findings may include muscle fasciculations, muscle cramps, and labile affect, but not necessarily mood. Regardless of initial symptoms, atrophy and weakness eventually affect other muscles. The mean age of onset is 56 years in individuals with no known family history and 46 years in individuals with more than one affected family member (familial ALS or FALS). Average disease duration is about three years, but it can vary significantly. Death usually results from compromise of the respiratory muscles. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1450]
Smith-Lemli-Opitz syndrome (SLOS) is a congenital multiple anomaly syndrome caused by an abnormality in cholesterol metabolism resulting from deficiency of the enzyme 7-dehydrocholesterol (7-DHC) reductase. It is characterized by prenatal and postnatal growth retardation, microcephaly, moderate to severe intellectual disability, and multiple major and minor malformations. The malformations include distinctive facial features, cleft palate, cardiac defects, underdeveloped external genitalia in males, postaxial polydactyly, and 2-3 syndactyly of the toes. The clinical spectrum is wide and individuals have been described with normal development and only minor malformations. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1143]
Peutz-Jeghers syndrome (PJS) is an autosomal-dominant condition characterized by the association of gastrointestinal polyposis, mucocutaneous pigmentation, and cancer predisposition. Peutz-Jeghers-type hamartomatous polyps are most common in the small intestine (in order of prevalence: in the jejunum, ileum, and duodenum) but can also occur in the stomach, large bowel, and extraintestinal sites including the renal pelvis, bronchus, gall bladder, nasal passages, urinary bladder, and ureters. Gastrointestinal polyps can result in chronic bleeding and anemia and also cause recurrent obstruction and intussusception requiring repeated laparotomy and bowel resection. Mucocutaneous hyperpigmentation presents in childhood as dark blue to dark brown macules around the mouth, eyes, and nostrils, in the perianal area, and on the buccal mucosa. Hyperpigmented macules on the fingers are common. The macules may fade in puberty and adulthood. Individuals with Peutz-Jeghers syndrome are at increased risk for a wide variety of epithelial malignancies (colorectal, gastric, pancreatic, breast, and ovarian cancers). Females are at risk for sex cord tumors with annular tubules (SCTAT), a benign neoplasm of the ovaries, and adenoma malignum of the cervix, a rare aggressive cancer. Males occasionally develop large calcifying Sertoli cell tumors (LCST) of the testes, which secrete estrogen and can lead to gynecomastia, advanced skeletal age, and ultimately short stature, if untreated. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1266]
Nuclear Gene-Encoded Leigh Syndrome Overview
Leigh syndrome (or subacute necrotizing encephalomyelopathy) is characterized by decompensation (often with elevated lactate levels in blood and/or CSF) during an intercurrent illness. It is typically associated with psychomotor retardation or regression, often followed by transient or prolonged stabilization or even improvement, but inevitably resulting in eventual progressive neurologic decline, typically occurring in stepwise decrements. Neurologic manifestations include hypotonia, spasticity, movement disorders (including chorea), cerebellar ataxia, and peripheral neuropathy. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK320989]
Oculopharyngeal muscular dystrophy (OPMD) is characterized by ptosis and swallowing difficulties due to selective involvement of the muscles of the eyelid and pharynx, respectively. The mean age of onset of ptosis is usually 48 years and onset of dysphagia is 50 years. Early symptoms of dysphagia are increased time needed to consume a meal and an acquired avoidance of dry foods. Swallowing difficulties determine prognosis, and increase the risk for potentially life-threatening aspiration pneumonia and poor nutrition. Other signs observed as the disease progresses are tongue weakness (82%), proximal lower-extremity weakness (71%), wet voice due to pooling of saliva (67%), limitation of upward gaze (61%), facial muscle weakness (43%), and proximal upper extremity weakness (38%). Involvement of the nervous system occurs on occasion. Severe OPMD, representing 5% to 10% of all OPMD, is characterized by onset of ptosis and dysphagia before age 45 years and incapacitating proximal leg weakness that starts before age 60 years. Some individuals with severe involvement eventually need a wheelchair. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1126]
Myoclonus-dystonia (M-D) is a movement disorder characterized by a combination of rapid, brief muscle contractions (myoclonus) and/or sustained twisting and repetitive movements that result in abnormal postures (dystonia). The myoclonic jerks typical of M-D most often affect the neck, trunk, and upper limbs with less common involvement of the legs. Approximately 50% of affected individuals have additional focal or segmental dystonia, presenting as cervical dystonia and/or writer's cramp. Non-motor features may include obsessive-compulsive disorder (OCD), depression, anxiety, personality disorders, alcohol abuse, and panic attacks. Symptom onset is usually in childhood or early adolescence but ranges from age six months to 80 years. Most affected adults report a dramatic reduction in myoclonus in response to alcohol ingestion. M-D is compatible with an active life of normal span. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1414]
Noonan syndrome (NS) is characterized by short stature, congenital heart defect, and developmental delay of variable degree. Other findings can include broad or webbed neck, unusual chest shape with superior pectus carinatum and inferior pectus excavatum, cryptorchidism, characteristic facies, varied coagulation defects, lymphatic dysplasias, and ocular abnormalities. Although birth length is usually normal, final adult height approaches the lower limit of normal. Congenital heart disease occurs in 50%-80% of individuals. Pulmonary valve stenosis, often with dysplasia, is the most common heart defect and is found in 20%-50% of individuals. Hypertrophic cardiomyopathy, found in 20%-30% of individuals, may be present at birth or develop in infancy or childhood. Other structural defects include atrial and ventricular septal defects, branch pulmonary artery stenosis, and tetralogy of Fallot. Up to one third of affected individuals have mild intellectual disability. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1124]
MELAS (mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes) is a multisystem disorder with onset typically in childhood. Early psychomotor development is usually normal, but short stature is common. Onset of symptoms is frequently between the ages of two and ten years. The most common initial symptoms are generalized tonic-clonic seizures, recurrent headaches, anorexia, and recurrent vomiting. Exercise intolerance or proximal limb weakness can be the initial manifestation. Seizures are often associated with stroke-like episodes of transient hemiparesis or cortical blindness. These stroke-like episodes may be associated with altered consciousness and may be recurrent. The cumulative residual effects of the stroke-like episodes gradually impair motor abilities, vision, and mentation, often by adolescence or young adulthood. Sensorineural hearing loss is common. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1233]
Familial hyperinsulinism (referred to as FHI in this GeneReview) is characterized by hypoglycemia that ranges from severe neonatal-onset, difficult-to-manage disease to childhood-onset disease with mild symptoms and difficult-to-diagnose hypoglycemia. Neonatal-onset disease manifests within hours to two days after birth. Childhood-onset disease manifests during the first months or years of life. In the newborn period, presenting symptoms may be nonspecific, including seizures, hypotonia, poor feeding, and apnea. In severe cases, serum glucose concentrations are typically extremely low and thus easily recognized, whereas in milder cases, variable and mild hypoglycemia may make the diagnosis more difficult. Even within the same family, disease manifestations can range from mild to severe. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1375]
IRF6-related disorders span a spectrum from isolated cleft lip and palate and Van der Woude syndrome (VWS) at the mild end to popliteal pterygium syndrome (PPS) at the more severe end. Congenital, usually bilateral, paramedian lower-lip fistulae (pits) or sometimes small mounds with a sinus tract leading from a mucous gland of the lip Cleft lip (CL) Cleft palate (CP)Note: Cleft lip with or without cleft palate (CL±P) is observed about twice as often as CP only. Submucous cleft palate (SMCP) [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1407]
GTP Cyclohydrolase 1-Deficient Dopa-Responsive Dystonia
GTP cyclohydrolase 1-deficient dopa-responsive dystonia (GTPCH1-deficient DRD) is characterized by childhood-onset dystonia and a dramatic and sustained response to low doses of oral administration of levodopa. The average age of onset is approximately six years. This disorder typically presents with gait disturbance caused by foot dystonia, later development of parkinsonism, and diurnal fluctuation of symptoms (aggravation of symptoms toward the evening and alleviation of symptoms in the morning after sleep). Initial symptoms are often gait difficulties attributable to flexion-inversion (equinovarus posture) of the foot. Occasionally, initial symptoms are arm dystonia, postural tremor of the hand, or slowness of movements. Brisk deep-tendon reflexes in the legs, ankle clonus, and/or the striatal toe (dystonic extension of the big toe) are present in many affected individuals. In general, gradual progression to generalized dystonia is observed. Intellectual, cerebellar, sensory, and autonomic disturbances generally do not occur. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1508]
Individuals with 22q11.2 deletion syndrome (22q11.2DS) have a range of findings including the following:Congenital heart disease (74% of individuals), particularly conotruncal malformations (tetralogy of Fallot, interrupted aortic arch, ventricular septal defect, and truncus arteriosus) Palatal abnormalities (69%), particularly velopharyngeal incompetence, submucosal cleft palate, bifid uvula, and cleft palate Characteristic facial features (present in the majority of individuals of northern European heritage) Learning difficulties (70%-90%) An immune deficiency (regardless of the clinical presentation) (77%) [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1523]
Hereditary Paraganglioma-Pheochromocytoma Syndromes
Hereditary paraganglioma-pheochromocytoma (PGL/PCC) syndromes are characterized by paragangliomas (tumors that arise from neuroendocrine tissues symmetrically distributed along the paravertebral axis from the base of the skull to the pelvis) and by pheochromocytomas (paragangliomas that are confined to the adrenal medulla). Sympathetic paragangliomas hypersecrete catecholamines; parasympathetic paragangliomas are most often nonsecretory. Extra-adrenal parasympathetic paragangliomas are located predominantly in the skull base, neck, and upper medistinum; approximately 95% of such tumors are nonsecretory. In contrast, sympathetic extra-adrenal paragangliomas are generally confined to the lower mediastinum, abdomen, and pelvis, and are typically secretory. Pheochromocytomas, which arise from the adrenal medulla, typically hypersecrete catecholamines. Symptoms of PGL/PCC result either from mass effects or catecholamine hypersecretion (e.g., sustained or paroxysmal elevations in blood pressure, headache, episodic profuse sweating, forceful palpitations, pallor, and apprehension or anxiety). The risk for malignant transformation is greater for extra-adrenal sympathetic paragangliomas than for pheochromocytomas or skull base and neck paragangliomas. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1548]
Autoimmune lymphoproliferative syndrome (ALPS), caused by defective lymphocyte homeostasis, is characterized by: Non-malignant lymphoproliferation (lymphadenopathy, hepatosplenomegaly with or without hypersplenism) that often improves with age; Autoimmune disease, mostly directed toward blood cells; and Lifelong increased risk for both Hodgkin and non-Hodgkin lymphoma. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1108]
Wilms tumor (nephroblastoma), an embryonal malignancy of the kidney, is the most common renal tumor of childhood. Wilms tumor usually presents as an abdominal mass in an otherwise apparently healthy child. Wilms tumor has the potential for both local and distant spread. Approximately 5%-10% of children with Wilms tumor have bilateral or multicentric tumors. The average age at presentation is 42-47 months for children with unilateral Wilms tumor and 30-33 months for those with bilateral Wilms tumor. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1294]
Phenylalanine hydroxylase (PAH) deficiency results in intolerance to the dietary intake of the essential amino acid phenylalanine and produces a spectrum of disorders including phenylketonuria (PKU), non-PKU hyperphenylalaninemia (non-PKU HPA), and variant PKU. Classic PKU is caused by a complete or near-complete deficiency of phenylalanine hydroxylase activity; without dietary restriction of phenylalanine, most children with PKU develop profound and irreversible intellectual disability. Non-PKU HPA is associated with a much lower risk of impaired cognitive development in the absence of treatment. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1504]
Familial transthyretin (TTR) amyloidosis is characterized by a slowly progressive peripheral sensorimotor neuropathy and autonomic neuropathy as well as non-neuropathic changes of cardiomyopathy, nephropathy, vitreous opacities, and CNS amyloidosis. The disease usually begins in the third to fifth decade in persons from endemic foci in Portugal and Japan; onset is later in persons from other areas. Typically, sensory neuropathy starts in the lower extremities with paresthesias and hypesthesias of the feet, followed within a few years by motor neuropathy. In some persons, particularly those with early onset disease, autonomic neuropathy is the first manifestation of the condition; findings can include: orthostatic hypotension, constipation alternating with diarrhea, attacks of nausea and vomiting, delayed gastric emptying, sexual impotence, anhidrosis, and urinary retention or incontinence. Cardiac amyloidosis is mainly characterized by progressive cardiomyopathy. Individuals with leptomeningeal amyloidosis may have the following CNS findings: dementia, psychosis, visual impairment, headache, seizures, motor paresis, ataxia, myelopathy, hydrocephalus, or intracranial hemorrhage. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1194]
FMR1-related disorders include fragile X syndrome, fragile X-associated tremor/ataxia syndrome (FXTAS), and FMR1-related primary ovarian insufficiency (POI). [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1384]
Genetic Atypical Hemolytic-Uremic Syndrome
Hemolytic-uremic syndrome (HUS) is characterized by hemolytic anemia, thrombocytopenia, and renal failure caused by platelet thrombi in the microcirculation of the kidney and other organs. Typical (acquired) HUS is triggered by infectious agents such as strains of E. coli (Stx-E. coli) that produce powerful Shiga-like exotoxins, whereas atypical HUS (aHUS) can be genetic, acquired, or idiopathic (of unknown cause). Onset of atypical HUS ranges from prenatal to adulthood. Individuals with genetic atypical HUS frequently experience relapse even after complete recovery following the presenting episode. Sixty percent of genetic aHUS progresses to end-stage renal disease (ESRD). [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1367]
ATP8B1 deficiency encompasses a phenotypic spectrum ranging from severe to intermediate to mild, based on an individual’s clinical findings and laboratory test results, including liver biopsy. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1297]
SCN1A-related seizure disorders encompass a spectrum that ranges from simple febrile seizures (FS) and generalized epilepsy with febrile seizures plus (GEFS+) at the mild end to Dravet syndrome and intractable childhood epilepsy with generalized tonic-clonic seizures (ICE-GTC) at the severe end. Phenotypes with intractable seizures including Dravet syndrome (also known as severe myoclonic epilepsy in infancy [SMEI] or polymorphic myoclonic epilepsy in infancy [PMEI]) are usually associated with progressive dementia. Less commonly observed phenotypes include myoclonic-astatic epilepsy (MAE or Doose syndrome), Lennox-Gastaut syndrome (LGS), infantile spasms, and vaccine-related encephalopathy and seizures. The phenotype of SCN1A-related seizure disorders can vary even within the same family. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1318]
Congenital Diaphragmatic Hernia Overview
Congenital diaphragmatic hernia (CDH) is characterized by: (1) incomplete formation/muscularization of the diaphragm resulting in absence or deficiency of the diaphragm, or (2) eventration resulting in elevation of a portion of the diaphragm that is thinned as a result of incomplete muscularization. Diaphragmatic hernias include posterolateral (Bochdalek) hernias, Morgagni and other anterior hernias, and (rarely) central hernias. About 50%-60% of affected individuals have isolated CDH; the remainder have complex CDH – that is, CDH occurring with additional malformations or as part of a single gene disorder or chromosome abnormality. Infants with CDH often present in the neonatal period with severe respiratory distress; pulmonary hypoplasia is common. Presenting symptoms after infancy can be acute onset of respiratory or gastrointestinal distress or abdominal pain from chronic intestinal obstruction or pleural effusion from entrapment of the bowel in the chest. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1359]
Junctional epidermolysis bullosa (JEB) is characterized by fragility of the skin and mucous membranes, manifest by blistering with little or no trauma. Blistering may be severe and granulation tissue can form on the skin around the oral and nasal cavities, fingers and toes, and internally around the upper airway. Blisters generally heal with no significant scarring. Broad classification of JEB includes Herlitz JEB (aka lethal) and non-Herlitz JEB (aka non-lethal). In Herlitz JEB, the classic severe form of JEB, blisters are present at birth or become apparent in the neonatal period. Congenital malformations of the urinary tract and bladder may also occur. In non-Herlitz JEB, the phenotype may be mild with blistering localized to hands, feet, knees, and elbows with or without renal or ureteral involvement. Some individuals never blister after the newborn period. Additional features shared by JEB and the other major forms of epidermolysis bullosa (EB) include congenital localized absence of skin (aplasia cutis congenita), milia, nail dystrophy, scarring alopecia, hypotrichosis, pseudosyndactyly, and other contractures. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1125]
Charcot-Marie-Tooth Hereditary Neuropathy Overview
Charcot-Marie-Tooth (CMT) hereditary neuropathy refers to a group of disorders characterized by a chronic motor and sensory polyneuropathy. The affected individual typically has distal muscle weakness and atrophy often associated with mild to moderate sensory loss, depressed tendon reflexes, and high-arched feet. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1358]
CADASIL (cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy) is characterized by mid-adult onset of recurrent ischemic stroke, cognitive decline progressing to dementia, a history of migraine with aura, mood disturbance, apathy, and diffuse white matter lesions and subcortical infarcts on neuroimaging. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1500]
Hermansky-Pudlak syndrome (HPS) is a multisystem disorder characterized by: tyrosinase-positive oculocutaneous albinism; a bleeding diathesis resulting from a platelet storage pool deficiency; and, in some cases, pulmonary fibrosis, granulomatous colitis, or immunodeficiency. The albinism is characterized by: hypopigmentation of the skin and hair; and ocular findings of reduced iris pigment with iris transillumination, reduced retinal pigment, foveal hypoplasia with significant reduction in visual acuity (usually in the range of 20/50 to 20/400), nystagmus, and increased crossing of the optic nerve fibers. Hair color ranges from white to brown; skin color ranges from white to olive and is usually a shade lighter than that of other family members. The bleeding diathesis can result in easy bruising, frequent epistaxis, gingival bleeding, postpartum hemorrhage, colonic bleeding, and prolonged bleeding with menses or after tooth extraction, circumcision, and other surgeries. Pulmonary fibrosis, a restrictive lung disease, typically causes symptoms in the early thirties and can progress to death within a decade. Granulomatous colitis is severe in about 15% of affected individuals. Neutropenia and/or immune defects are associated primarily with HPS-2. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1287]
Fabry disease results from deficient activity of the enzyme α-galactosidase (α-Gal A) and progressive lysosomal deposition of globotriaosylceramide (GL-3) in cells throughout the body. The classic form, occurring in males with less than 1% α-Gal A enzyme activity, usually has its onset in childhood or adolescence with periodic crises of severe pain in the extremities (acroparesthesias), the appearance of vascular cutaneous lesions (angiokeratomas), sweating abnormalities (anhydrosis, hypohydosis, and rarely hyperhidrosis), characteristic corneal and lenticular opacities, and proteinuria. Gradual deterioration of renal function to end-stage renal disease (ESRD) usually occurs in men in the third to fifth decade. In middle age, most males successfully treated for ESRD develop cardiac and/or cerebrovascular disease, a major cause of morbidity and mortality. Heterozygous females typically have milder symptoms at a later age of onset than males. Rarely, they may be relatively asymptomatic throughout a normal life span or may have symptoms as severe as those observed in males with the classic phenotype. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1292]
DYT1 early-onset primary dystonia typically presents in childhood or adolescence and only on occasion in adulthood. Dystonic muscle contractions causing posturing of a foot, leg, or arm are the most common presenting findings. Dystonia is usually first apparent with specific actions such as writing or walking. Over time, the contractions frequently (but not invariably) become evident with less specific actions and spread to other body regions. No other neurologic abnormalities are present, except for postural arm tremor. Disease severity varies considerably even within the same family. Isolated writer's cramp may be the only sign. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1492]
Brugada syndrome is characterized by cardiac conduction abnormalities (ST-segment abnormalities in leads V1-V3 on ECG and a high risk for ventricular arrhythmias) that can result in sudden death. Brugada syndrome presents primarily during adulthood; although age at diagnosis ranges from two days to 85 years. The mean age of sudden death is approximately 40 years. Clinical presentations may also include sudden infant death syndrome (SIDS; death of a child during the first year of life without an identifiable cause) and the sudden unexpected nocturnal death syndrome (SUNDS), a typical presentation in individuals from Southeast Asia. Other conduction defects can include first-degree AV block, intraventricular conduction delay, right bundle branch block, and sick sinus syndrome. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1517]
Craniofacial microsomia (CFM) includes a spectrum of malformations primarily involving structures derived from the first and second branchial arches. Characteristic findings include facial asymmetry resulting from maxillary and/or mandibular hypoplasia; preauricular or facial tags; ear malformations that can include microtia (hypoplasia of the external ear), anotia (absence of the external ear), or aural atresia (absence of the external ear canal); and hearing loss. Severity can range from subtle facial asymmetry with a small skin tag in front of an otherwise normal-appearing ear to bilateral involvement (typically asymmetric), microtia/anotia with atresia of the ear canals, microphthalmia, and respiratory compromise from severe mandibular hypoplasia. Other craniofacial malformations including cleft lip and/or palate can be seen. Non-craniofacial malformations, especially vertebral, renal, cardiac, and limb, can be seen. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK5199]
Arrhythmogenic Right Ventricular Cardiomyopathy
Arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C) is characterized by progressive fibrofatty replacement of the myocardium that predisposes to ventricular tachycardia and sudden death in young individuals and athletes. It primarily affects the right ventricle; with time, it may also involve the left ventricle. The presentation of disease is highly variable even within families, and some affected individuals may not meet established clinical criteria. The mean age at diagnosis is 31 years (±13; range: 4-64 years). [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1131]
Chorea-acanthocytosis (ChAc) is characterized by a progressive movement disorder, cognitive and behavior changes, a myopathy that can be subclinical, and chronic hyperCKemia in serum. Although the disorder is named for acanthocytosis of the red blood cells, this feature is variable. The movement disorder is mostly limb chorea, but some individuals present with parkinsonism. Dystonia is common and affects the oral region and especially the tongue, causing dysarthria and serious dysphagia with resultant weight loss. Habitual tongue and lip biting are characteristic, as well as tongue protrusion dystonia. Progressive cognitive and behavioral changes resemble those in a frontal lobe syndrome. Seizures are observed in almost half of affected individuals and can be the initial manifestation. Myopathy results in progressive distal muscle wasting and weakness. Mean age of onset in ChAc is about 30 years, although ChAc can develop as early as the first decade or as late as the seventh decade. It runs a chronic progressive course and may lead to major disability within a few years. Life expectancy is reduced, with age of death ranging from 28 to 61 years. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1387]
Medium-Chain Acyl-Coenzyme A Dehydrogenase Deficiency
Medium-chain acyl-coenzyme A dehydrogenase (MCAD) is one of the enzymes involved in mitochondrial fatty acid β-oxidation, which fuels hepatic ketogenesis, a major source of energy once hepatic glycogen stores become depleted during prolonged fasting and periods of higher energy demands. In a typical clinical scenario, a previously healthy child with MCAD deficiency presents with hypoketotic hypoglycemia, vomiting, and lethargy triggered by a common illness. Seizures may occur. Hepatomegaly and liver disease are often present during an acute episode, which can quickly progress to coma and death. Children are normal at birth and – if not identified through newborn screening – typically present between ages three and 24 months; later presentation, even into adulthood, is possible. The prognosis is excellent once the diagnosis is established and frequent feedings are instituted to avoid any prolonged period of fasting. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1424]
Isolated methylmalonic acidemia/aciduria is caused by complete or partial deficiency of the enzyme methylmalonyl-CoA mutase (mut0 enzymatic subtype or mut– enzymatic subtype, respectively), a defect in the transport or synthesis of its cofactor, adenosyl-cobalamin (cblA, cblB, or cblD variant 2 type), or deficiency of the enzyme methylmalonyl-CoA epimerase. Onset of the manifestations of isolated methylmalonic acidemia/aciduria ranges from the neonatal period to adulthood. All phenotypes demonstrate periods of relative health and intermittent metabolic decompensation, usually associated with intercurrent infections and stress. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1231]
Malignant hyperthermia susceptibility (MHS) is a pharmacogenetic disorder of skeletal muscle calcium regulation associated with uncontrolled skeletal muscle hypermetabolism. Manifestations of malignant hyperthermia (MH) are precipitated by certain volatile anesthetics (i.e., halothane, isoflurane, sevoflurane, desflurane, enflurane), either alone or in conjunction with a depolarizing muscle relaxant (specifically, succinylcholine). The triggering substances release calcium stores from the sarcoplasmic reticulum and may promote entry of calcium from the myoplasm, causing contracture of skeletal muscles, glycogenolysis, and increased cellular metabolism, resulting in production of heat and excess lactate. Affected individuals experience: acidosis, hypercapnia, tachycardia, hyperthermia, muscle rigidity, compartment syndrome, rhabdomyolysis with subsequent increase in serum creatine kinase (CK) concentration, hyperkalemia with a risk for cardiac arrhythmia or even arrest, and myoglobinuria with a risk for renal failure. In nearly all cases, the first manifestations of MH (tachycardia and tachypnea) occur in the operating room; however, MH may also occur in the early postoperative period. There is mounting evidence that some affected individuals will also develop MH with exercise and/or on exposure to hot environments. Without proper and prompt treatment with dantrolene sodium, mortality is extremely high. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1146]
Von Hippel-Lindau (VHL) syndrome is characterized by hemangioblastomas of the brain, spinal cord, and retina; renal cysts and clear cell renal cell carcinoma; pheochromocytoma, pancreatic cysts, and neuroendocrine tumors; endolymphatic sac tumors; and epididymal and broad ligament cysts. Cerebellar hemangioblastomas may be associated with headache, vomiting, gait disturbances, or ataxia. Spinal hemangioblastomas and related syrinx usually present with pain. Sensory and motor loss may develop with cord compression. Retinal hemangioblastomas may be the initial manifestation of VHL syndrome and can cause vision loss. Renal cell carcinoma occurs in about 70% of individuals with VHL and is the leading cause of mortality. Pheochromocytomas can be asymptomatic but may cause sustained or episodic hypertension. Pancreatic lesions often remain asymptomatic and rarely cause endocrine or exocrine insufficiency. Endolymphatic sac tumors can cause hearing loss of varying severity, which can be a presenting symptom. Cystadenomas of the epididymis are relatively common. They rarely cause problems, unless bilateral, in which case they may result in infertility. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1463]
Arylsulfatase A deficiency (also known as metachromatic leukodystrophy or MLD) is characterized by three clinical subtypes: late-infantile MLD (50%-60% of cases); juvenile MLD (20%-30% of cases); and adult MLD (15%-20% of cases). Age of onset within a family is usually similar. The disease course may be from three to ten or more years in the late-infantile form and up to 20 years or more in the juvenile and adult forms. Late-infantile MLD. Onset is between ages one and two years. Typical presenting findings include weakness, hypotonia, clumsiness, frequent falls, toe walking, and slurred speech. Later signs include inability to stand, difficulty with speech, deterioration of mental function, increased muscle tone, pain in the arms and legs, generalized or partial seizures, compromised vision and hearing, and peripheral neuropathy. In the final stages children have tonic spasms, decerebrate posturing, and general unawareness of their surroundings. Juvenile MLD. Onset is between age four years and sexual maturity (age 12-14 years). Initial manifestations include decline in school performance and emergence of behavioral problems, followed by clumsiness, gait problems, slurred speech, incontinence, and bizarre behaviors. Seizures may occur. Progression is similar to but slower than the late-infantile form. Adult MLD. Onset occurs after sexual maturity, sometimes not until the fourth or fifth decade. Initial signs can include problems in school or job performance, personality changes, alcohol or drug abuse, poor money management, and emotional lability; in others, neurologic symptoms (weakness and loss of coordination progressing to spasticity and incontinence) or seizures predominate initially. Peripheral neuropathy is common. Disease course is variable, with periods of stability interspersed with periods of decline, and may extend over two to three decades. The final stage is similar to that for the earlier-onset forms. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1130]
Ornithine transcarbamylase (OTC) deficiency can occur as a severe neonatal-onset disease in males (but rarely in females) and as a late-onset (partial) disease in males and females. Males with severe neonatal-onset OTC deficiency are typically normal at birth but become symptomatic from hyperammonemia on day two to three of life and are usually catastrophically ill by the time they come to medical attention. After successful treatment of neonatal hyperammonemic coma these infants can easily become hyperammonemic again despite appropriate treatment; they typically require liver transplant by age six months to improve quality of life. Males and heterozygous females with late-onset (partial) OTC deficiency can present from infancy to later childhood, adolescence, or adulthood. No matter how mild the disease, a hyperammonemic crisis can be precipitated by stressors and become a life-threatening event at any age and in any situation in life. For all individuals with OTC deficiency, typical neuropsychological complications include developmental delay, learning disabilities, intellectual disability, attention deficit hyperactivity disorder (ADHD), and executive function deficits. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK154378]
Holoprosencephaly (HPE) is a structural anomaly of the brain in which there is failed or incomplete separation of the forebrain early in gestation. Classic HPE encompasses a continuum of brain malformations including (in order of decreasing severity): alobar, semilobar, lobar, and middle interhemispheric variant (MIHV) type HPE; a septopreoptic type has also been described. Other CNS abnormalities not specific to HPE may also occur. HPE is accompanied by a spectrum of characteristic craniofacial anomalies in approximately 80% of individuals with HPE. Developmental delay is present in virtually all individuals with the HPE spectrum of CNS anomalies. Seizures and pituitary dysfunction are common. Most affected fetuses do not survive; severely affected children typically do not survive beyond early infancy, while a significant proportion of more mildly affected children survive past 12 months. Mildly manifesting individuals without appreciable brain anomalies on conventional neuroimaging may be described as having “microform” HPE. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1530]
Congenital Disorders of N-Linked Glycosylation and Multiple Pathway Overview
Congenital disorders of N-linked glycosylation (abbreviated here as CDG-N-linked), are a group of disorders of N-linked oligosaccharides caused by deficiency in 42 different enzymes in the N-linked synthetic pathway. Most commonly, the disorders begin in infancy; manifestations range from severe developmental delay and hypotonia with multiple organ system involvement to hypoglycemia and protein-losing enteropathy with normal development. However, most types have been described in only a few individuals, and thus understanding of the phenotypes is limited. In PMM2-CDG (CDG-Ia), the most common type reported, the clinical presentation and course are highly variable, ranging from death in infancy to mild involvement in adults. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1332]
Hereditary hemorrhagic telangiectasia (HHT) is characterized by the presence of multiple arteriovenous malformations (AVMs) that lack intervening capillaries and result in direct connections between arteries and veins. Although HHT is a developmental disorder and infants are occasionally severely affected, in most people the features are age-dependent and the diagnosis not suspected until adolescence or later. Small AVMs (or telangiectases) close to the surface of the skin and mucous membranes often rupture and bleed after slight trauma. The most common clinical manifestation is spontaneous and recurrent nosebleeds (epistaxis) beginning on average at age 12 years. Approximately 25% of individuals with HHT have GI bleeding, which most commonly begins after age 50 years. Large AVMs often cause symptoms when they occur in the brain, liver, or lungs; complications from bleeding or shunting may be sudden and catastrophic. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1351]
Classic ataxia-telangiectasia (A-T) is characterized by progressive cerebellar ataxia beginning between ages one and four years, oculomotor apraxia, choreoathetosis, telangiectasias of the conjunctivae, immunodeficiency, frequent infections, and an increased risk for malignancy, particularly leukemia and lymphoma. Individuals with A-T are unusually sensitive to ionizing radiation. Non-classic forms of A-T have included adult-onset A-T and A-T with early-onset dystonia. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK26468]
Spinocerebellar ataxia type 3 (SCA3), also known as Machado-Joseph disease (MJD), is characterized by progressive cerebellar ataxia and variable findings including a dystonic-rigid syndrome, a parkinsonian syndrome, or a combined syndrome of dystonia and peripheral neuropathy. Neurologic findings tend to evolve as the disease progresses. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1196]
Bardet-Biedl syndrome (BBS) is characterized by rod-cone dystrophy, truncal obesity, postaxial polydactyly, cognitive impairment, male hypogonadotrophic hypogonadism, complex female genitourinary malformations, and renal abnormalities. The visual prognosis for children with BBS is poor. Night blindness is usually evident by age seven to eight years; the mean age of legal blindness is 15.5 years. Birth weight is usually normal, but significant weight gain begins within the first year and becomes a lifelong issue for most individuals. A majority of individuals have significant learning difficulties; a minority have severe impairment on IQ testing. Renal disease is a major cause of morbidity and mortality. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1363]
The hereditary spastic paraplegias (HSPs) are clinically and genetically heterogeneous disorders characterized by lower extremity spasticity and weakness (occurring in variable proportion). When symptoms begin after childhood, they usually progress slowly and steadily. When symptoms begin in very early childhood, they may be non-progressive and resemble spastic diplegic cerebral palsy. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1509]
The eight disorders comprising the FGFR-related craniosynostosis spectrum are Pfeiffer syndrome, Apert syndrome, Crouzon syndrome, Beare-Stevenson syndrome, FGFR2-related isolated coronal synostosis, Jackson-Weiss syndrome, Crouzon syndrome with acanthosis nigricans (AN), and Muenke syndrome (isolated coronal synostosis caused by the p.Pro250Arg pathogenic variant in FGFR3). Muenke syndrome and FGFR2-related isolated coronal synostosis are characterized only by uni- or bicoronal craniosynostosis; the remainder are characterized by bicoronal craniosynostosis or cloverleaf skull, distinctive facial features, and variable hand and foot findings. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1455]
Calpainopathy is characterized by symmetric and progressive weakness of proximal (limb-girdle) muscles. The age at onset of muscle weakness ranges from two to 40 years. The phenotype shows intra- and interfamilial variability ranging from mild to severe. Three calpainopathy phenotypes have been identified based on the distribution of muscle weakness and age at onset: Pelvifemoral limb-girdle muscular dystrophy (LGMD) (Leyden-Möbius LGMD) phenotype, the most frequently observed calpainopathy phenotype, in which muscle weakness is first evident in the pelvic girdle and later in the shoulder girdle, with onset before age 12 years or after age 30 years Scapulohumeral LGMD (Erb LGMD) phenotype, usually a milder phenotype with infrequent early onset, in which muscle weakness is first evident in the shoulder girdle and later in the pelvic girdle HyperCKemia, usually observed in children or young individuals, in which asymptomatic individuals have only high serum creatine kinase (CK) concentrations [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1313]
Spinal muscular atrophy (SMA) is characterized by progressive muscle weakness resulting from degeneration and loss of the anterior horn cells (i.e., lower motor neurons) in the spinal cord and the brain stem nuclei. Onset ranges from before birth to adolescence or young adulthood. Poor weight gain, sleep difficulties, pneumonia, scoliosis, and joint contractures are common complications. Before the genetic basis of SMA was understood, it was classified into clinical subtypes; however, it is now apparent that the phenotype of SMA associated with disease-causing mutations of SMN1 spans a continuum without clear delineation of subtypes. Nonetheless, classification by age of onset and maximum function achieved is useful for prognosis and management; subtypes include: SMA 0 (proposed), with prenatal onset and severe joint contractures, facial diplegia, and respiratory failure; SMA I, with onset before age six months; SMA II, with onset between age six and 12 months; SMA III, with onset in childhood after age 12 months and ability to walk at least 25 meters achieved; and SMA IV, with adult onset. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1352]
Williams syndrome (WS) is characterized by cardiovascular disease (elastin arteriopathy, peripheral pulmonary stenosis, supravalvar aortic stenosis, hypertension), distinctive facies, connective tissue abnormalities, intellectual disability (usually mild), a specific cognitive profile, unique personality characteristics, growth abnormalities, and endocrine abnormalities (hypercalcemia, hypercalciuria, hypothyroidism, and early puberty). Feeding difficulties often lead to failure to thrive in infancy. Hypotonia and hyperextensible joints can result in delayed attainment of motor milestones. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1249]
Multiple endocrine neoplasia type 2 (MEN 2) is classified into three subtypes: MEN 2A, FMTC (familial medullary thyroid carcinoma), and MEN 2B. All three subtypes involve high risk for development of medullary carcinoma of the thyroid (MTC); MEN 2A and MEN 2B have an increased risk for pheochromocytoma; MEN 2A has an increased risk for parathyroid adenoma or hyperplasia. Additional features in MEN 2B include mucosal neuromas of the lips and tongue, distinctive facies with enlarged lips, ganglioneuromatosis of the gastrointestinal tract, and a ‘marfanoid’ habitus. MTC typically occurs in early childhood in MEN 2B, early adulthood in MEN 2A, and middle age in FMTC. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1257]
Hereditary diffuse gastric cancer (HDGC) is an autosomal dominant susceptibility for diffuse gastric cancer, a poorly differentiated adenocarcinoma that infiltrates into the stomach wall causing thickening of the wall (linitis plastica) without forming a distinct mass. Diffuse gastric cancer is also referred to as signet ring carcinoma or isolated cell-type carcinoma. The average age of onset of HDGC is 38 years, with a range of 14-69 years. The majority of the cancers in individuals with a CDH1 pathogenic variant occur before age 40 years. The estimated cumulative risk of gastric cancer by age 80 years is 80% for both men and women. Women also have a 39%-52% risk for lobular breast cancer. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1139]
Myotonic dystrophy type 1 (DM1) is a multisystem disorder that affects skeletal and smooth muscle as well as the eye, heart, endocrine system, and central nervous system. The clinical findings, which span a continuum from mild to severe, have been categorized into three somewhat overlapping phenotypes: mild, classic, and congenital.Mild DM1 is characterized by cataract and mild myotonia (sustained muscle contraction); life span is normal. Classic DM1 is characterized by muscle weakness and wasting, myotonia, cataract, and often cardiac conduction abnormalities; adults may become physically disabled and may have a shortened life span. Congenital DM1 is characterized by hypotonia and severe generalized weakness at birth, often with respiratory insufficiency and early death; intellectual disability is common. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1165]
LRRK2-related Parkinson disease (PD) is characterized by features consistent with idiopathic PD: initial motor features of slowly progressive asymmetric tremor at rest and/or bradykinesia, cog-wheel muscle rigidity, postural instability, and gait abnormalities that may include festination and freezing. Non-motor symptoms in LRRK2-related PD occur with similar frequency as observed in typical idiopathic PD. Onset is generally after age 50 years. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1208]
Classic Joubert syndrome is characterized by three primary findings: A distinctive cerebellar and brain stem malformation called the molar tooth sign (MTS) Hypotonia Developmental delays [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1325]
Angelman syndrome (AS) is characterized by severe developmental delay or intellectual disability, severe speech impairment, gait ataxia and/or tremulousness of the limbs, and a unique behavior with an inappropriate happy demeanor that includes frequent laughing, smiling, and excitability. Microcephaly and seizures are also common. Developmental delays are first noted at around age six months; however, the unique clinical features of AS do not become manifest until after age one year, and it can take several years before the correct clinical diagnosis is obvious. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1144]
Lynch syndrome, caused by a germline pathogenic variant in a mismatch repair gene and associated with tumors exhibiting microsatellite instability (MSI), is characterized by an increased risk for colon cancer and cancers of the endometrium, ovary, stomach, small intestine, hepatobiliary tract, urinary tract, brain, and skin. In individuals with Lynch syndrome the following life time risks for cancer are seen: 52%-82% for colorectal cancer (mean age at diagnosis 44-61 years); 25%-60% for endometrial cancer in women (mean age at diagnosis 48-62 years); 6% to 13% for gastric cancer (mean age at diagnosis 56 years); and 4%-12% for ovarian cancer (mean age at diagnosis 42.5 years; approximately 30% are diagnosed before age 40 years). The risk for other Lynch syndrome-related cancers is lower, though substantially increased over general population rates. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1211]
Tuberous sclerosis complex (TSC) involves abnormalities of the skin (hypomelanotic macules, facial angiofibromas, shagreen patches, cephalic plaques, ungual fibromas); brain (cortical dysplasias, subependymal nodules and subependymal giant cell astrocytomas [SEGAs], seizures, intellectual disability/developmental delay, psychiatric illness); kidney (angiomyolipomas, cysts, renal cell carcinomas); heart (rhabdomyomas, arrhythmias); and lungs (lymphangioleiomyomatosis [LAM]). CNS tumors are the leading cause of morbidity and mortality; renal disease is the second leading cause of early death. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1220]
Gaucher disease (GD) encompasses a continuum of clinical findings from a perinatal lethal disorder to an asymptomatic type. The identification of three major clinical types (1, 2, and 3) and two other subtypes (perinatal-lethal and cardiovascular) is useful in determining prognosis and management. GD type 1 is characterized by the presence of clinical or radiographic evidence of bone disease (osteopenia, focal lytic or sclerotic lesions, and osteonecrosis), hepatosplenomegaly, anemia and thrombocytopenia, lung disease, and the absence of primary central nervous system disease. GD types 2 and 3 are characterized by the presence of primary neurologic disease; in the past, they were distinguished by age of onset and rate of disease progression, but these distinctions are not absolute. Disease with onset before age two years, limited psychomotor development, and a rapidly progressive course with death by age two to four years is classified as GD type 2. Individuals with GD type 3 may have onset before age two years, but often have a more slowly progressive course, with survival into the third or fourth decade. The perinatal-lethal form is associated with ichthyosiform or collodion skin abnormalities or with nonimmune hydrops fetalis. The cardiovascular form is characterized by calcification of the aortic and mitral valves, mild splenomegaly, corneal opacities, and supranuclear ophthalmoplegia. Cardiopulmonary complications have been described with all the clinical subtypes, although varying in frequency and severity. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1269]
The hereditary ataxias are a group of genetic disorders characterized by slowly progressive incoordination of gait and often associated with poor coordination of hands, speech, and eye movements. Frequently, atrophy of the cerebellum occurs. In this GeneReview the hereditary ataxias are categorized by mode of inheritance and gene (or chromosome locus) in which pathogenic variants occur. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1138]
Mitochondrial DNA-Associated Leigh Syndrome and NARP
Mitochondrial (mt) DNA-associated Leigh syndrome and NARP (neurogenic muscle weakness, ataxia, and retinitis pigmentosa) are part of a continuum of progressive neurodegenerative disorders caused by abnormalities of mitochondrial energy generation.Leigh syndrome (or subacute necrotizing encephalomyelopathy) is characterized by onset of symptoms typically between age three and 12 months, often following a viral infection. Decompensation (often with elevated lactate levels in blood and/or CSF) during an intercurrent illness is typically associated with psychomotor retardation or regression. Neurologic features include hypotonia, spasticity, movement disorders (including chorea), cerebellar ataxia, and peripheral neuropathy. Extraneurologic manifestations may include hypertrophic cardiomyopathy. About 50% of affected individuals die by age three years, most often as a result of respiratory or cardiac failure. NARP is characterized by proximal neurogenic muscle weakness with sensory neuropathy, ataxia, and pigmentary retinopathy. Onset of symptoms, particularly ataxia and learning difficulties, is often in early childhood. Individuals with NARP can be relatively stable for many years, but may suffer episodic deterioration, often in association with viral illnesses. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1173]
Friedreich ataxia (FRDA) is characterized by slowly progressive ataxia with mean onset between age ten and 15 years and usually before age 25 years. FRDA is typically associated with dysarthria, muscle weakness, spasticity in the lower limbs, scoliosis, bladder dysfunction, absent lower limb reflexes, and loss of position and vibration sense. Approximately two thirds of individuals with FRDA have cardiomyopathy; up to 30% have diabetes mellitus; and approximately 25% have an "atypical" presentation with later onset or retained tendon reflexes. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1281]
MECP2-related disorders in females include classic Rett syndrome, variant Rett syndrome, and mild learning disabilities. A pathogenic MECP2 variant in a male is presumed to most often be lethal; phenotypes in rare surviving males are primarily severe neonatal encephalopathy and manic-depressive psychosis, pyramidal signs, Parkinsonian, and macro-orchidism (PPM-X syndrome). [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1497]
Emery-Dreifuss muscular dystrophy (EDMD) is characterized by the clinical triad of joint contractures that begin in early childhood, slowly progressive muscle weakness and wasting initially in a humero-peroneal distribution that later extends to the scapular and pelvic girdle muscles, and cardiac involvement that may manifest as palpitations, presyncope and syncope, poor exercise tolerance, and congestive heart failure. Age of onset, severity, and progression of muscle and cardiac involvement demonstrate both inter- and intrafamilial variability. Clinical variability ranges from early onset with severe presentation in childhood to late onset with slow progression in adulthood. In general, joint contractures appear during the first two decades, followed by muscle weakness and wasting. Cardiac involvement usually occurs after the second decade. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1436]
Prader-Willi (PWS) syndrome is characterized by severe hypotonia and feeding difficulties in early infancy, followed in later infancy or early childhood by excessive eating and gradual development of morbid obesity (unless eating is externally controlled). Motor milestones and language development are delayed. All individuals have some degree of cognitive impairment. A distinctive behavioral phenotype (with temper tantrums, stubbornness, manipulative behavior, and obsessive-compulsive characteristics) is common. Hypogonadism is present in both males and females and manifests as genital hypoplasia, incomplete pubertal development, and, in most, infertility. Short stature is common; characteristic facial features, strabismus, and scoliosis are often present, and non-insulin-dependent diabetes mellitus often occurs in obese individuals. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1330]
The dystrophinopathies include a spectrum of muscle disease caused by pathogenic variants in DMD, which encodes the protein dystrophin. The mild end of the spectrum includes the phenotypes of asymptomatic increase in serum concentration of creatine phosphokinase (CK) and muscle cramps with myoglobinuria. The severe end of the spectrum includes progressive muscle diseases that are classified as Duchenne/Becker muscular dystrophy when skeletal muscle is primarily affected and as DMD-associated dilated cardiomyopathy (DCM) when the heart is primarily affected. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1119]
Fanconi anemia (FA) is characterized by physical abnormalities, bone marrow failure, and increased risk of malignancy. Physical abnormalities, present in 60%-75% of affected individuals, include one or more of the following: short stature; abnormal skin pigmentation; malformations of the thumbs, forearms, skeletal system, eyes, kidneys and urinary tract, ears (and decreased hearing), heart, gastrointestinal system, central nervous system; hypogonadism; and developmental delay. Progressive bone marrow failure with pancytopenia typically presents in the first decade, often initially with thrombocytopenia or leukopenia. By age 40 to 50 years, the estimated cumulative incidence of bone marrow failure is 90%; the incidence of hematologic malignancies (primarily acute myeloid leukemia) 10%-30%; and of nonhematologic malignancies (solid tumors, particularly of the head and neck, skin, GI tract, and genital tract) 25%-30%. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1401]
APC-associated polyposis conditions include: familial adenomatous polyposis (FAP), attenuated FAP, Gardner syndrome, and Turcot syndrome. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1345]
Huntington disease (HD) is a progressive disorder of motor, cognitive, and psychiatric disturbances. The mean age of onset is 35 to 44 years and the median survival time is 15 to 18 years after onset. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1305]
Multiple endocrine neoplasia type 1 (MEN1) syndrome includes varying combinations of more than 20 endocrine and non-endocrine tumors.Parathyroid tumors are the main MEN1-associated endocrinopathy; onset in 90% of individuals is between ages 20 and 25 years with hypercalcemia evident by age 50 years; hypercalcemia causes lethargy, depression, confusion, anorexia, constipation, nausea, vomiting, diuresis, dehydration, hypercalciuria, kidney stones, increased bone resorption/fracture risk, hypertension, and shortened QT interval. Pituitary tumors include prolactinoma (the most common) which manifests as oligomenorrhea/amenorrhea and galactorrhea in females and sexual dysfunction in males. Well-differentiated endocrine tumors of the gastro-entero-pancreatic (GEP) tract can manifest as Zollinger-Ellison syndrome (gastrinoma); hypoglycemia (insulinoma); hyperglycemia, anorexia, glossitis, anemia, diarrhea, venous thrombosis, and skin rash (glucagonoma); and watery diarrhea, hypokalemia, and achlorhydria syndrome (vasoactive intestinal peptide [VIP]-secreting tumor). Carcinoid tumors are non-hormone-secreting and can manifest as a large mass after age 50 years. Adrenocortical tumors can be associated with primary hypercortisolism or hyperaldosteronism. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1538]
Sickle cell disease (SCD) is characterized by intermittent vaso-occlusive events and chronic hemolytic anemia. Vaso-occlusive events result in tissue ischemia leading to acute and chronic pain as well as organ damage that can affect any organ in the body, including the bones, lungs, liver, kidneys, brain, eyes, and joints. Dactylitis (pain and/or swelling of the hands or feet) in infants and young children is often the earliest manifestation of sickle cell disease. In children the spleen can become engorged with blood cells in a “splenic sequestration.” The spleen is particularly subject to infarction and the majority of individuals with SCD are functionally asplenic in early childhood, increasing their risk for certain types of bacterial infections. Chronic hemolysis can result in varying degrees of anemia, jaundice, cholelithiasis, and delayed growth and sexual maturation. Individuals with the highest rates of hemolysis are predisposed to pulmonary artery hypertension, priapism, and leg ulcers but may be relatively protected from vaso-occlusive pain. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1377]
Familial Mediterranean fever (FMF) comprises two phenotypes: type 1 and type 2. FMF type 1 is characterized by recurrent short episodes of inflammation and serositis including fever, peritonitis, synovitis, pleuritis, and, rarely, pericarditis and meningitis. The symptoms and severity vary among affected individuals, sometimes even among members of the same family. Amyloidosis, which can lead to renal failure, is the most severe complication. FMF type 2 is characterized by amyloidosis as the first clinical manifestation of FMF in an otherwise asymptomatic individual. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1227]
Primary hyperoxaluria type 1 (PH1) is caused by a deficiency of the liver peroxisomal enzyme alanine:glyoxylate-aminotransferase (AGT), which catalyzes the conversion of glyoxylate to glycine. When AGT activity is absent, glyoxylate is converted to oxalate, which forms insoluble calcium salts that accumulate in the kidney and other organs. Individuals with PH1 are at risk for recurrent nephrolithiasis (deposition of calcium oxalate in the renal pelvis/urinary tract), nephrocalcinosis (deposition of calcium oxalate in the renal parenchyma), or end-stage renal disease (ESRD) with a history of renal stones or calcinosis. Age at onset of symptoms typically ranges from one to 25 years. Approximately 19% of affected individuals present before age four to six months with severe disease, often associated with failure to thrive, nephrocalcinosis, anemia, and metabolic acidosis. Approximately 54% of affected individuals present in late childhood or early adolescence, usually with symptomatic nephrolithiasis. The remainder of affected individuals present in adulthood with recurrent renal stones. The natural history of untreated PH1 is one of inexorable decline in renal function as a result of progressive nephrolithiasis/nephrocalcinosis, with eventual progression to oxalosis (widespread tissue deposition of calcium oxalate) and death from ESRD. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1283]
Polycystic Kidney Disease, Autosomal Dominant
Autosomal dominant polycystic kidney disease (ADPKD) is generally a late-onset multisystem disorder characterized by: bilateral renal cysts; cysts in other organs including the liver, seminal vesicles, pancreas, and arachnoid membrane; vascular abnormalities including intracranial aneurysms, dilatation of the aortic root, and dissection of the thoracic aorta; mitral valve prolapse; and abdominal wall hernias. Renal manifestations include hypertension, renal pain, and renal insufficiency. Approximately 50% of individuals with ADPKD have end-stage renal disease (ESRD) by age 60 years. The prevalence of liver cysts, the most common extrarenal manifestation of ADPKD, increases with age and may have been underestimated by ultrasound studies. The prevalence of intracranial aneurysms is higher in those with a positive family history of aneurysms or subarachnoid hemorrhage (22%) than in those without such a family history (6%). Mitral valve prolapse, the most common valvular abnormality, occurs in up to 25% of affected individuals. Substantial variability in severity of renal disease and other extrarenal manifestations occurs even within the same family. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1246]
BRCA1- and BRCA2-Associated Hereditary Breast and Ovarian Cancer
Hereditary breast and ovarian cancer syndrome (HBOC), caused by a germline pathogenic variant in BRCA1 or BRCA2, is characterized by an increased risk for breast cancer, ovarian cancer, prostate cancer, and pancreatic cancer. The lifetime risk for these cancers in individuals with a pathogenic variant in BRCA1 or BRCA2:40%-80% for breast cancer 11%-40% for ovarian cancer 1%-10% for male breast cancer Up to 39% for prostate cancer 1%-7% for pancreatic cancer [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1247]
Neurofibromatosis 1 (NF1) is characterized by multiple café-au-lait spots, axillary and inguinal freckling, multiple cutaneous neurofibromas, and iris Lisch nodules. Learning disabilities are present in at least 50% of individuals with NF1. Less common but potentially more serious manifestations include plexiform neurofibromas, optic nerve and other central nervous system gliomas, malignant peripheral nerve sheath tumors, scoliosis, tibial dysplasia, and vasculopathy. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1109]
Prothrombin-related thrombophilia is characterized by venous thromboembolism (VTE) manifest most commonly in adults as deep-vein thrombosis (DVT) in the legs or pulmonary embolism. The clinical expression of prothrombin-related thrombophilia is variable; many individuals heterozygous or homozygous for the 20210G>A (G20210A or c.*97G>A) allele in F2 never develop thrombosis, and while most heterozygotes who develop thrombotic complications remain asymptomatic until adulthood, some have recurrent thromboembolism before age 30 years. The relative risk for DVT in adults heterozygous for the 20210G>A allele is two- to fivefold increased; in children, the relative risk for thrombosis is three- to fourfold increased. 20210G>A heterozygosity has at most a modest effect on recurrence risk after a first episode. Although prothrombin-related thrombophilia may increase the risk for pregnancy loss, its association with preeclampsia and other complications of pregnancy such as intrauterine growth restriction and placental abruption remains controversial. Factors that predispose to thrombosis in prothrombin-related thrombophilia include: the number of 20210G>A alleles; presence of coexisting genetic abnormalities including factor V Leiden; and acquired thrombophilic disorders (e.g., antiphospholipid antibodies). Circumstantial risk factors for thrombosis include pregnancy and oral contraceptive use. Some evidence suggests that the risk for VTE in 20210G>A heterozygotes increases after travel. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1148]
Factor V Leiden thrombophilia is characterized by a poor anticoagulant response to activated protein C (APC) and an increased risk for venous thromboembolism (VTE). Deep venous thrombosis (DVT) is the most common VTE, with the legs being the most common site. Thrombosis in unusual locations is less common. Evidence suggests that a heterozygous factor V Leiden mutation has at most a modest effect on recurrence risk after initial treatment of a first VTE. Heterozygosity for factor V Leiden is associated with a two- to threefold increase in relative risk for pregnancy loss, and possibly other pregnancy complications such as preeclampsia, fetal growth retardation, and placental abruption. The clinical expression of factor V Leiden thrombophilia is influenced by: The number of factor V Leiden alleles (heterozygotes have a slightly increased risk for venous thrombosis; homozygotes have a much greater thrombotic risk); Coexisting genetic thrombophilic disorders, which have a supra-additive effect on overall thrombotic risk; Acquired thrombophilic disorders: antiphospholipid antibodies, hyperhomocysteinemia, high factor VIII levels, malignancy; and Circumstantial risk factors: travel, central venous catheters, pregnancy, oral contraceptive use, hormone replacement therapy (HRT), selective estrogen receptor modulators (SERMs), organ transplantation, advancing age, and surgery. [GeneReviews:NBK1116, GeneReviews:NBK138602, GeneReviews:NBK1368]