Nine different neurodegenerative disorders are known to be caused by expansions of polyglutamine-encoding CAG trinucleotide (CAGpolyQ) repeats in the following genes: the HD gene in Huntington disease [1], ATN1 in dentatorubral pallidoluysian atrophy or Haw River syndrome [2,3], AR in spinal and bulbar muscular atrophy [4], CACNA1A in spinocerebellar ataxia SCA6 [5], TBP in SCA17 [6] and ATXN1, 2, 3, and 7 in SCA1 [7], SCA2 [8-10], SCA3 (Machado-Joseph disease) [11], and SCA7 [12]. The gene discussed is ATN1; the disease is Huntington disease.