SCA3, Machado type
Machado-Joseph disease type 3 is a subtype of Machado-Joseph disease (SCA3/MJD, see this term) of milder severity characterized by late onset, slower progression, and peripheral amyotrophy. The prevalence of this form of MJD is not known. It accounts for 30% of all SCA3 cases. The mean age of onset is 46 years and signs include cerebellar ataxia and external progressive ophthalmoplegia along with peripheral amyotrophy, with or without mild pyramidal and extrapyramidal features. The disease is caused by CAG repeat expansion mutations in the ATXN3 gene (14q21). MJD follows an autosomal dominant pattern of inheritance.