Spinocerebellar Ataxia Type 20

Spinocerebellar ataxia type 20 (SCA20) is a very rare subtype of type I autosomal dominant cerebellar ataxia (ADCA type I; see this term). It is characterized by cerebellar dysarthria as the initial typical manifestation.

Epidemiology

Prevalence is unknown. Fewer than 20 cases in a 4-generation Australian family of Anglo-Celtic descent have been reported to date.

Clinical description

Age of symptomatic disease onset ranges from 19 to 64 years (mean age = 46.5 years). Most affected patients also exhibit palatal tremor and spasmodic dysphonia. Head computed tomography (CT) shows dentate calcifications.

Etiology

SCA20 has been linked to chromosome 11q12.2-11q12.3, overlapping with the locus for SCA5 (see this term), though clinical features differ. SCA5 belongs to type III ADCA (see this term) and represents a pure ataxia syndrome with on average earlier age of symptomatic disease onset ranging from 14 to 50 years. Since the causative gene is unknown, SCA20 and SCA5 may be proven genetically to be the same disorder.

Prognosis

Prognosis is relatively good. Most patients can walk with or without gait aids and many patients live to more than 60 years of age.