Autosomal recessive spinocerebellar ataxia is a neurologic disorder characterized by onset of progressive gait difficulties, eye movement abnormalities, and dysarthria in the first or second decade of life (summary by Dy et al., 2015).

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.

Spinocerebellar ataxia-21 (SCA21) is an autosomal dominant neurologic disorder characterized by onset in the first decades of life of slowly progressive cerebellar ataxia, which is associated with cognitive impairment in most patients (summary by Delplanque et al., 2014). For a general discussion of autosomal dominant spinocerebellar ataxia, see SCA1 (164400).

VPS13D movement disorder is a hyperkinetic movement disorder (dystonia, chorea, and/or ataxia) of variable age of onset that can be associated with developmental delay. Onset ranges from birth to adulthood. Individuals can present in childhood with motor delays and gait instability. Cognitive impairment ranging from mild intellectual disability to developmental delay has been reported, and several individuals have normal cognitive function. Individuals have also presented as young adults with gait difficulties caused by spastic ataxia or ataxia. In addition to gait ataxia, affected individuals had limb ataxia, dysarthria, and eye movement abnormalities (macro-saccadic oscillations, nystagmus, and saccadic pursuit). Additional features reported in some individuals include peripheral neuropathy and/or seizures. The disorder progresses to spastic ataxia or generalized dystonia, which can lead to loss of independent ambulation.

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 vestibuloocular 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.

A rare disease with characteristics of slowly progressive and relatively pure ataxia described in 6 patients from one Australian family to date. The disease presents with oculomotor dysfunction, moderate dysarthria, and ataxia that progresses slowly and eventually leads to mobility impairment. Some patients have also reported mild hyperreflexia in the lower limbs. Rare manifestations include gaze-evoked nystagmus and dystonia. The causal gene has not yet been identified but it has been linked to chromosome 4q34.3-q35.1.

Autosomal recessive spinocerebellar ataxia-10 is an autosomal recessive neurodegenerative disorder with onset in the teenage or young adult years of gait and limb ataxia, dysarthria, and nystagmus associated with marked cerebellar atrophy on brain imaging (summary by Vermeer et al., 2010). Some patients have low levels of coenzyme Q10 (CoQ10) in muscle and may show some clinical improvement with CoQ10 treatment (Balreira et al., 2014).

Autosomal recessive spinocerebellar ataxia-27 (SCAR27) is an adult-onset neurologic disorder characterized by gait difficulties and other cerebellar signs, such as eye movement abnormalities, dysarthria, and difficulty writing. The disorder is progressive, and some patients may lose independent ambulation. Additional features include spasticity of the lower limbs and cognitive impairment. Brain imaging shows cerebellar atrophy (summary by Eidhof et al., 2018).

Myoclonic dystonia-34 (DYT34) is an autosomal dominant neurologic disorder characterized by childhood-onset dystonia primarily involving the hands and neck, with a fast tremor with superimposed myoclonus (Balint et al., 2020).

Autosomal recessive spinocerebellar ataxia-32 (SCAR32) is a neurologic disorder characterized by the onset of gait ataxia in the second or third decades of life. The disorder is slowly progressive. Other classic features include upper limb ataxia, oculomotor signs, dysphagia, and dysarthria. Some patients may have hyper- or hypokinetic movement abnormalities. Brain imaging shows cerebellar atrophy (Rebelo et al., 2021).