ATXN3 and autosomal dominant cerebellar ataxia: Spinocerebellar ataxia type 3 (SCA3), also named Machado–Joseph disease (MJD), is an autosomal dominant cerebellar ataxia associated with the expansion of the ATXN3 exon 10 CAG repeat to 45 copies or more, resulting in a mutant ataxin-3 protein with an expanded poly-glutamine (polyQ) tract.