Spinocerebellar ataxia type 12 (SCA12) is a very rare subtype of type I autosomal dominant cerebellar ataxia (ADCA type I; see this term). It is characterized by the presence of action tremor associated with relatively mild cerebellar ataxia. Associated pyramidal and extrapyramidal signs and dementia have been reported.
Prevalence is unknown. Approximately 40 families have been reported.
The age of symptomatic onset ranges from 8 to 55 years with most patients presenting in the 4th decade.
Like SCA8 the pathogenesis of SCA12 seems to be related to a toxic effect at the RNA level as it is caused by a CAG expansion at the 5' end of the PPP2R2B gene on chromosome 5q31-5q32.
Prognosis is essentially good. In many cases progression of the illness is slow and in general life expectancy is not affected.