MedGen

Typical Friedreich ataxia (FRDA) is characterized by progressive ataxia with onset from early childhood to early adulthood with mean age at onset from 10 to 15 years (range: age two years to the eighth decade). Ataxia, manifesting initially as poor balance when walking, is typically followed by upper-limb ataxia, dysarthria, dysphagia, peripheral motor and sensory neuropathy, spasticity, autonomic disturbance, and often abnormal eye movements and optic atrophy. Hypertrophic cardiomyopathy is present in about two thirds of individuals; occasionally it is diagnosed prior to the onset of ataxia. Diabetes mellitus and impaired glucose tolerance can also occur. Among individuals with FRDA, about 75% have "typical Friedreich ataxia" and about 25% of individuals with biallelic FXN full-penetrance GAA repeat expansions have "atypical Friedreich ataxia" that includes late-onset FRDA (LOFA) (i.e., onset after age 25 years), very late-onset FRDA (VLOFA) (i.e., onset after age 40 years), and FRDA with retained reflexes (FARR). [from GeneReviews]

GJB1 disorders are typically characterized by peripheral motor and sensory neuropathy with or without fixed CNS abnormalities and/or acute, self-limited episodes of transient neurologic dysfunction (especially weakness and dysarthria). Peripheral neuropathy typically manifests in affected males between ages five and 25 years. Although both men and women are affected, manifestations tend to be less severe in women, some of whom may remain asymptomatic. Less commonly, initial manifestations in some affected individuals are stroke-like episodes (acute fulminant episodes of reversible CNS dysfunction). [from GeneReviews]

Spinocerebellar ataxia type 6 (SCA6) is characterized by adult-onset, slowly progressive cerebellar ataxia, dysarthria, and nystagmus. The age of onset ranges from 19 to 73 years; mean age of onset is between 43 and 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. [from GeneReviews]

VPS13A disease, caused by VPS13A loss-of-function pathogenic variants, is characterized by a spectrum of movement disorders (chorea, dystonia, tics, sometimes parkinsonism); predominant orofacial choreic and dystonic movements and tics (with involuntary tongue protrusion on attempted swallowing, habitual tongue and lip biting resulting in self-mutilation, involuntary vocalizations); dysarthria and dysphagia; psychiatric, cognitive, and behavioral changes ("frontal lobe type"); seizures; and progressive neuromuscular involvement. Huntingtonism (triad of progressive movement disorder and cognitive and behavioral alterations) is a typical presentation. Phenotypic variability is considerable even within the same family, including for monozygotic twins. Mean age of onset is about 30 years. VPS13A disease runs a chronic progressive course and may lead to major disability within a few years. Some affected individuals are bedridden or wheelchair dependent by the third decade. Age at death ranges from 28 to 61 years; several instances of sudden unexplained death or death during epileptic seizures have been reported. [from GeneReviews]

Single large-scale mitochondrial DNA deletion syndromes (SLSMDSs) comprise overlapping clinical phenotypes including Kearns-Sayre syndrome (KSS), KSS spectrum, Pearson syndrome (PS), chronic progressive external ophthalmoplegia (CPEO), and CPEO-plus. KSS is a progressive multisystem disorder with onset before age 20 years characterized by pigmentary retinopathy, CPEO, and cardiac conduction abnormality. Additional features can include cerebellar ataxia, tremor, intellectual disability or cognitive decline, dementia, sensorineural hearing loss, oropharyngeal and esophageal dysfunction, exercise intolerance, muscle weakness, and endocrinopathies. Brain imaging typically shows bilateral lesions in the globus pallidus and white matter. KSS spectrum includes individuals with KSS in addition to individuals with ptosis and/or ophthalmoparesis and at least one of the following: retinopathy, ataxia, cardiac conduction defects, hearing loss, growth deficiency, cognitive impairment, tremor, or cardiomyopathy. Compared to CPEO-plus, individuals with KSS spectrum have more severe muscle involvement (e.g., weakness, atrophy) and overall have a worse prognosis. PS is characterized by pancytopenia (typically transfusion-dependent sideroblastic anemia with variable cell line involvement), exocrine pancreatic dysfunction, poor weight gain, and lactic acidosis. PS manifestations also include renal tubular acidosis, short stature, and elevated liver enzymes. PS may be fatal in infancy due to neutropenia-related infection or refractory metabolic acidosis. CPEO is characterized by ptosis, ophthalmoplegia, oropharyngeal weakness, variable proximal limb weakness, and/or exercise intolerance. CPEO-plus includes CPEO with additional multisystemic involvement including neuropathy, diabetes mellitus, migraines, hypothyroidism, neuropsychiatric manifestations, and optic neuropathy. Rarely, an SLSMDS can manifest as Leigh syndrome, which is characterized as developmental delays, neurodevelopmental regression, lactic acidosis, and bilateral symmetric basal ganglia, brain stem, and/or midbrain lesions on MRI. [from GeneReviews]

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 in affected males. Affected individuals often show gynecomastia, testicular atrophy, and reduced fertility as a result of mild androgen insensitivity. [from GeneReviews]

The autosomal dominant TRPV4 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 each group is considerable. Affected individuals typically have either neuromuscular or skeletal manifestations alone, and in only rare instances an overlap syndrome has been reported. The three autosomal dominant neuromuscular disorders (mildest to most severe) are: Charcot-Marie-Tooth disease type 2C. Scapuloperoneal spinal muscular atrophy. Congenital distal spinal muscular atrophy. The autosomal dominant neuromuscular disorders are characterized by a congenital-onset, static, or later-onset progressive peripheral neuropathy with variable combinations of laryngeal dysfunction (i.e., vocal fold paresis), respiratory dysfunction, and joint contractures. The six autosomal dominant skeletal dysplasias (mildest to most severe) are: Familial digital arthropathy-brachydactyly. Autosomal dominant brachyolmia. Spondylometaphyseal dysplasia, Kozlowski type. Spondyloepiphyseal dysplasia, Maroteaux type. Parastremmatic dysplasia. Metatropic dysplasia. The skeletal dysplasia is characterized by brachydactyly (in all 6); the five that are more severe have short stature that varies from mild to severe with progressive spinal deformity and involvement of the long bones and pelvis. In the mildest of the autosomal dominant TRPV4 disorders life span is normal; in the most severe it is shortened. Bilateral progressive sensorineural hearing loss (SNHL) can occur with both autosomal dominant neuromuscular disorders and skeletal dysplasias. [from GeneReviews]

GNPTAB-related disorders comprise the phenotypes mucolipidosis II (ML II) and mucolipidosis IIIa/ß (ML IIIa/ß), and phenotypes intermediate between ML II and ML IIIa/ß. ML II is evident at birth and slowly progressive; death most often occurs in early childhood. Orthopedic abnormalities present at birth may include thoracic deformity, kyphosis, clubfeet, deformed long bones, and/or dislocation of the hip(s). Growth 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. All children 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. ML IIIa/ß becomes evident at about age three years with slow growth rate and short stature; joint stiffness and pain initially in the shoulders, hips, and fingers; gradual mild coarsening of facial features; and normal to mildly impaired cognitive development. Pain from osteoporosis becomes more severe during adolescence. Cardiorespiratory complications (restrictive lung disease, thickening and insufficiency of the mitral and aortic valves, left and/or right ventricular hypertrophy) are common causes of death, typically in early to middle adulthood. Phenotypes intermediate between ML II and ML IIIa/ß are characterized by physical growth in infancy that resembles that of ML II and neuromotor and speech development that resemble that of ML IIIa/ß. [from GeneReviews]

COMP-related pseudoachondroplasia (COMP-PSACH) 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 COMP-PSACH eventually require hip replacement surgery. [from GeneReviews]

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 with characteristic brain MRI features that include thinning of the corpus callosum. Onset occurs mainly during infancy or adolescence (range: age 1-31 years) and in rare cases as late as age 60 years. Most affected individuals become wheelchair bound one or two decades after disease onset. [from GeneReviews]

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 by 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. [from GeneReviews]

A severe form of axonal Charcot-Marie-Tooth disease, a peripheral sensorimotor neuropathy, with onset in the 2nd or 3rd decade, characterised by ulcerations and infections of feet. Symmetric and distal weakness develops mostly in the legs together with a severe symmetric distal sensory loss, tendon reflexes are only reduced at ankles and foot deformities, including pes cavus or planus and hammer toes, appear in childhood. [from SNOMEDCT_US]

X-linked recessive Charcot-Marie-Tooth disease-4 with or without cerebellar ataxia (CMTX4) is a mitochondrial disorder manifest as progressive neurologic dysfunction with highly variable features. The age at onset ranges from infancy to young adulthood, and patients can present with different features, including hearing loss, delayed motor development, or difficulty walking due to peripheral neuropathy and/or cerebellar ataxia. Most patients develop all features, including a progressive sensorimotor axonal neuropathy and deafness due to auditory neuropathy. Additional more variable features can include cognitive impairment, cerebellar atrophy on brain imaging, cerebellar signs, such as dysarthria, abnormal extraocular movements, tremor, and dysmetria, as well as spasticity. There is significant intrafamilial variability: the variable features are consistent with mitochondrial dysfunction. Prolonged treatment with riboflavin may result in some mild improvement in the ataxia (summary by Rinaldi et al., 2012, Heimer et al., 2018, Bogdanova-Mihaylova et al., 2019). [from OMIM]

SCA8 is a slowly progressive ataxia with onset typically in the third to fifth decade but with a range from before age one year to after age 60 years. Common initial manifestations are scanning dysarthria with a characteristic drawn-out slowness of speech and gait instability. Over the disease course other findings can include eye movement abnormalities (nystagmus, abnormal pursuit and abnormal saccades, and, rarely, ophthalmoplegia); upper motor neuron involvement; extrapyramidal signs; brain stem signs (dysphagia and poor cough reflex); sensory neuropathy; and cognitive impairment (e.g., executive dysfunction, psychomotor slowing and other features of cerebellar cognitive-affective disorder in some). Life span is typically not shortened. [from GeneReviews]

Mitochondrial DNA-associated Leigh syndrome spectrum (mtDNA-LSS) is part of a continuum of progressive neurodegenerative disorders caused by abnormalities of mitochondrial energy generation, which includes the overlapping phenotypes mtDNA-associated Leigh syndrome and mtDNA-associated Leigh-like syndrome. Mitochondrial DNA-LSS is characterized by onset of manifestations typically between ages three and 12 months, often following an intercurrent illness (usually viral) or metabolic challenge (vaccinations, surgery, prolonged fasting). Decompensation (often with elevated lactate levels in blood and/or cerebrospinal fluid) is typically associated with developmental delay and/or regression. Neurologic features include hypotonia, spasticity, seizures, movement disorders, cerebellar ataxia, and peripheral neuropathy. Brain stem dysfunction may manifest with respiratory symptoms, swallowing difficulties, ophthalmoparesis, and abnormalities in thermoregulation. Extraneurologic manifestations may include poor weight gain, cardiomyopathy, and conduction defects. Up to 50% of individuals die by age three years, most often from respiratory or cardiac failure. [from GeneReviews]

DNMT1-related disorder is a degenerative disorder of the central and peripheral nervous systems comprising a phenotypic spectrum that includes hereditary sensory and autonomic neuropathy type 1E (HSAN1E) and autosomal dominant cerebellar ataxia, deafness, and narcolepsy (ADCA-DN). DNMT1 disorder is often characterized by moderate-to-severe sensorineural hearing loss beginning in the teens or early 20s, sensory impairment, sudomotor dysfunction (loss of sweating), and dementia usually beginning in the mid-40s. In some affected individuals, narcolepsy/cataplexy syndrome and ataxia are predominant findings. [from GeneReviews]

Spinocerebellar ataxia with axonal neuropathy type 1 (SCAN1) is characterized by late-childhood-onset slowly progressive cerebellar ataxia and distal sensorimotor axonal neuropathy. Gaze nystagmus and dysarthria usually develop after the onset of ataxic gait. As the disease advances, pain and touch sensation in the hands and feet become impaired; vibration sense is lost in hands and lower thighs. Individuals with advanced disease develop a steppage gait and pes cavus and eventually become wheelchair dependent. Cognitive dysfunction – present in some – manifests as mild intellectual disability and poor executive function. To date only seven affected individuals have been described from three apparently unrelated consanguineous families (one from Saudi Arabia and two from Oman); therefore, it is likely that the full phenotypic spectrum of this disorder is not yet known. [from GeneReviews]

ADCADN is an autosomal dominant neurologic disorder characterized by adult onset of progressive cerebellar ataxia, narcolepsy/cataplexy, sensorineural deafness, and dementia. More variable features include optic atrophy, sensory neuropathy, psychosis, and depression (summary by Winkelmann et al., 2012). [from OMIM]

Spinocerebellar ataxia type 4 (SCA4) is a progressive neurologic disease characterized by cerebellar involvement (gait ataxia, balance disturbances, eye movement abnormalities), brain stem involvement (dysarthria, dysphagia), sensory neuropathy, motor neuron involvement (muscle wasting and spasticity), autonomic dysfunction (especially orthostatic hypotension), and cognition and/or behavior manifestations. Age of onset ranges from 12 to 65 years. In the approximately 10% of individuals whose onset is before age 25 years disease manifestations are more severe and often different from those with later-onset disease. As the disease progresses, particularly in those with early-onset disease, eye movement abnormalities, dysarthria, dysphagia, sensory neuropathy, upper and lower motor neuron involvement, and orthostatic hypotension can further aggravate balance and gait problems. Most individuals eventually require a walker or wheelchair. Reduced life expectancy in individuals with earlier-onset severe SCA4 is associated with weight loss, infections, and cardiac arrhythmia. Life expectancy is normal or near normal in individuals with later-onset SCA4. [from GeneReviews]

In patients with SSMED, short stature and microcephaly are apparent at birth, and there is progressive postnatal growth failure. Endocrine dysfunction, including hypergonadotropic hypogonadism, multinodular goiter, and diabetes mellitus, is present in affected adults. Progressive ataxia has been reported in some patients, with onset ranging from the second to fifth decade of life. In addition, a few patients have developed tumors, suggesting that there may be a predisposition to tumorigenesis. In contrast to syndromes involving defects in other components of the nonhomologous end-joining (NHEJ) complex (see, e.g., 606593), no clinically overt immunodeficiency has been observed in SSMED, although laboratory analysis has revealed lymphopenia or borderline leukopenia in some patients (Murray et al., 2015; Bee et al., 2015; de Bruin et al., 2015; Guo et al., 2015). [from OMIM]