SCA3, caused by an expanded CAG repeat in the ATXN3 gene (Kawaguchi et al., 1994), is one of the most common dominantly inherited ataxias worldwide (Gaspar et al., 2001; Schols et al., 2004) and is characterized by cerebellar degeneration and progressive ataxia. The gene discussed is ATXN3; the disease is Ataxia.