In Machado-Joseph disease (MJD), also known as spinocerebellar ataxia type 3 (SCA3), the affected protein ataxin-3 is characterized by a pathological expansion of a C-terminally located polyglutamine (polyQ) stretch, encoded by a CAG repeat in the ATXN3 gene. Here, ATXN3 is linked to Spinocerebellar ataxia type 3.