Thomas type SCA3
Machado-Joseph disease type 2 is a subtype of Machado-Joseph disease (SCA3/MJD, see this term) with intermediate severity characterized by an intermediate age of onset, cerebellar ataxia and external progressive ophthalmoplegia, with variable pyramidal and extrapyramidal signs. The prevalence of this form of MJD is not known. It is the most frequent form of SCA3 and accounts for 57% of all SCA3 cases. Patients develop the disease in middle adulthood (mean age 40 years). If present, extrapyramidal and peripheral manifestations are mild. Some patients progress within 5 to 10 years to type 1 MJD (see this term) if significant extrapyramidal signs develop, or type 3 MJD (see this term) if significant peripheral signs appear. The disease is caused by CAG repeat expansion mutations in the ATXN3 gene (14q21). MJD follows an autosomal dominant pattern of inheritance.