ATXN7 and Huntington disease: At least ten neurodegenerative disorders are caused by poly-Q expansions, including Huntington's disease (HD), dentatorubral and pallidoluysian atrophy (DRPLA), spinal and bulbar muscular atrophy (SBMA), and the poly-Q spinocerebellar ataxias [2] (SCA1, SCA2, SCA3, SCA6, SCA7, SCA8, and SCA17) [3-5].