Abnormal expansion of a stretch of glutamine residues in the C‐terminus of ATXN3 is causative for spinocerebellar ataxia type 3 (SCA3), also known as Machado–Joseph disease, the most common hereditary type of ataxia (Kawaguchi et al., 1994). The gene discussed is ATXN3; the disease is Spinocerebellar ataxia type 3.