The CAG repeat number of these genes in the normal population is less than a certain threshold (14–44 repeats), whereas the CAG repeat number in SCA3 patients is a complete mutation (52–86 repeats).[1–4] SCA3 is characterized by cerebellar ataxia, which is the main symptom that progressively worsens. This evidence concerns the gene ATXN3 and cerebellar ataxia.