ATXN3 and Machado-Joseph disease: Spinocerebellar ataxia type 3 (SCA3), also known as Machado-Joseph disease (MJD), is an autosomal dominantly inherited ataxia which is characterized by deficits in gait, movement, and coordination linked to a CAG repeat expansion in the ATXN3 gene and a concordant polyglutamine expansion in the ataxin-3 protein.