Spinocerebellar Ataxia Type 6

Clinical characteristics: 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.

Diagnosis/testing: The diagnosis of SCA6 rests on the use of molecular genetic testing to detect an abnormal CAG trinucleotide repeat expansion in CACNA1A. Affected individuals have 20 to 33 CAG repeats.

Management: Treatment of manifestations: Acetazolamide may eliminate episodes of ataxia; canes, walking sticks, and walkers to prevent falling; home modifications for safety and convenience; weighted eating utensils and dressing hooks; physical therapy and exercises enhancing balance and core strength; vitamin supplements particularly if caloric intake is reduced; feeding recommendations as per feeding therapist / occupational therapist; weight control, as obesity exacerbates ambulation and mobility problems; vestibular symptoms may be managed with medications including diphenhydramine, baclofen, and gabapentin. 4-aminopyridine may be helpful with vestibular symptoms and to suppress nystagmus; refractive or surgical management per ophthalmologist for diplopia; speech therapy and communication devices for dysarthria; clonazepam for REM sleep disorders; continuous positive airway pressure for sleep apnea.

Surveillance: Annual or semiannual evaluation by a neurologist; driving ability should be assessed by professionals periodically. Annual consultations with a physiatrist and physical and/or occupational therapist; review need for walking aid(s) and home adaptations. Nutrition evaluation, video esophagram, and feeding assessments as needed. Ophthalmology and/or optometry evaluation as needed for prisms or surgery.

Agents/circumstances to avoid: Sedative hypnotics (ethanol or certain medications) that increase incoordination.

Genetic counseling: SCA6 is inherited in an autosomal dominant manner. Offspring of an affected individual have a 50% chance of inheriting an abnormal CAG trinucleotide repeat expansion in CACNA1A. Once a CACNA1A CAG repeat expansion has been identified in an affected family member, prenatal testing and preimplantation genetic testing for SCA6 are possible.