Dentatorubral-pallidoluysian atrophy (DRPLA) is a very rare, dominantly inherited disorder reported in all populations, but most often in the Japanese population. Neuropathology is wide-ranging and includes degeneration of the dentatorubal and pallidoluysian circuits. Most DRPLA patients display progressive cerebellar ataxia, choreoatheosis, epilepsy, and dementia, while juvenile-onset cases include myoclonus and mental retardation. DRPLA is caused by an unstable CAG repeat in the atrophin-1 gene coding region. Normal alleles in the atrophin-1 gene contain 8-25 CAG repeats, while patient expansions range in 49-88 CAGs.