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.

Disease with characteristics of early-onset tremor, dyskinesia and slowly progressive cerebellar ataxia. Fewer than 30 cases have been reported to date. This disease is caused by a mutation in the fibroblast growth factor 14 FGF14 gene (13q34). Prognosis is relatively good. Life-threatening status epilepticus and intractable seizure or severe dysphagia is rare.

Autosomal dominant sensory ataxia-1 (SNAX1) is a peripheral neuropathy resulting from the degeneration of dorsal root ganglia that affects both central and peripheral neurites of sensory neurons. Affected individuals show adult onset of slowly progressive clumsiness, gait ataxia, walking difficulties, and distal sensory loss which may be associated with abnormal sensory nerve conduction values. Some patients have vestibular ocular dysfunction. Muscle weakness and atrophy are not observed, and brain imaging is normal (summary by Cortese et al., 2020).