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 upgaze 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 after 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.

Retinopathy-sensory neuropathy syndrome (RETSNS) is an autosomal recessive disorder characterized by progressive visual impairment due to retinopathy (usually retinitis pigmentosa) and progressive sensory neuropathy resulting in distal sensory loss of various modalities (vibration, proprioception, pain). Affected individuals have noncerebellar gait ataxia, presumably due to degeneration of dorsal root ganglia in the posterior column of the spinal cord. The phenotypic manifestations and severity of the disorder are highly variable, and the age at onset can range from infancy to young adulthood. Individuals can present with either visual problems or sensory impairment with gait ataxia, but most patients eventually develop both. More severely affected individuals have congenital insensitivity to pain presenting in infancy, resulting in chronic ulceration and osteomyelitis. Autonomic abnormalities may also be apparent, consistent with hereditary sensory and autonomic neuropathy (HSAN; see, e.g., 162400). Developmental delay or impaired intellectual development is sometimes observed (Higgins et al., 1997; Grudzinska Pechhacker et al., 2020; Calame et al., 2025).

Untreated ataxia with vitamin E deficiency (AVED) generally manifests between ages five and 15 years. The first manifestations include progressive ataxia, clumsiness of the hands, loss of proprioception, and areflexia. Other features often observed are dysdiadochokinesia, dysarthria, positive Romberg sign, head titubation, decreased visual acuity, and positive Babinski sign. Although age of onset and disease course are more uniform within a given family, disease manifestations and their severity can vary even among sibs. When lifelong high-dose vitamin E supplementation is initiated in presymptomatic individuals, manifestations of AVED do not develop.

Ataxia with oculomotor apraxia type 2 (AOA2) is characterized by onset of ataxia between age three and 30 years after initial normal development, axonal sensorimotor neuropathy, oculomotor apraxia, cerebellar atrophy, and elevated serum concentration of alpha-fetoprotein (AFP).

Autosomal recessive familial visceral neuropathy-1 (VSCN1) is characterized by a broad spectrum of developmental anomalies associating neural crest and extraneural crest features, including intestinal dysmotility due to aganglionosis (Hirschsprung disease), hypoganglionosis, and/or chronic intestinal pseudoobstruction. Some patients develop progressive peripheral neuropathy, and arthrogryposis has been observed. Hypoplasia or aplasia of the olfactory bulb and of the external auditory canals, as well as microtia or anotia, have been reported. Patients also exhibit facial dysmorphisms, including microretrognathia in most; other variable features include structural cardiac anomalies and arthrogryposis with multiple pterygia (Le et al., 2021). Genetic Heterogeneity of Familial Visceral Neuropathy Autosomal recessive familial visceral neuropathy-2 (VSCN2; 619465) is caused by mutation in the ERBB2 gene (164870) on chromosome 17q12. Also see VSCN3 (609629) for an autosomal dominant form of the disorder.

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.

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).

Spastic paraplegia-79B (SPG79B) is an autosomal recessive progressive neurologic disorder characterized by onset of spastic paraplegia and optic atrophy in the first decade of life. Additional features are variable, but may include peripheral neuropathy, cerebellar ataxia, and cognitive impairment (summary by Rydning et al., 2017). For a discussion of genetic heterogeneity of autosomal recessive spastic paraplegia, see SPG5A (270800).

Spinocerebellar ataxia-35 (SCA35) is an autosomal dominant adult-onset neurologic disorder characterized by difficulty walking due to cerebellar ataxia. The age at onset ranges from teenage years to late adulthood, and the disorder is slowly progressive. Additional features may include hand tremor, dysarthria, hyperreflexia, and saccadic eye movements (summary by Guo et al., 2014). For a general discussion of autosomal dominant spinocerebellar ataxia, see SCA1 (164400).

Hereditary sensory and autonomic neuropathy type VIII (HSAN8) is an autosomal recessive neurologic disorder characterized by congenital insensitivity to pain resulting in ulceration to the fingers, tongue, lips, and other distal appendages. Affected individuals may also have decreased sweating and tear production (summary by Chen et al., 2015). For a discussion of genetic heterogeneity of hereditary sensory and autonomic neuropathy, see HSAN1A (162400).

Mitochondrial axonal Charcot-Marie-Tooth disease (CMTMA) is inherited only through the maternal line. The disorder is characterized by onset of distal muscle weakness and atrophy mainly affecting the lower limbs and resulting in difficulty walking in the second decade of life, although both earlier and later onset can occur. Upper limb involvement often develops with time, and affected individuals have weakness and atrophy of the intrinsic hand muscles. Other features may include distal sensory impairment, foot deformities, scoliosis, hypo- or hyperreflexia, spastic paraparesis, and neurogenic bladder. Electrophysiologic studies are compatible with an axonal sensorimotor peripheral neuropathy, and muscle and nerve biopsy show evidence of mitochondrial dysfunction with decreased activities of respiratory complexes, mtDNA deletions, and mitochondrial hyperplasia (summary by Fay et al., 2020).

Autosomal recessive spastic paraplegia-85 (SPG85) is a neurologic disorder characterized by the onset of motor symptoms in the first few years of life. Affected individuals have spasticity and hyperreflexia of the lower limbs resulting in gait abnormalities. Older patients may have upper limb involvement and demonstrate axonal polyneuropathy. Additional features include optic atrophy, dysarthria, dysphagia, ataxia, and urinary incontinence. Brain imaging may show cerebellar atrophy (summary by Wagner et al., 2019). For a discussion of genetic heterogeneity of autosomal recessive spastic paraplegia, see SPG5A (270800).