Their disease origins, identical to other polyQ diseases [Huntington’s disease (HD), dentatorubral pallidoluysian atrophy (DRPLA), spinal and bulbar muscular atrophy, and X-linked 1 disease (SMAX1/SBMA)], have been traced to the abnormal expansion of CAG repeats in the coding region of disease-associated genes. This evidence concerns the gene AR and Huntington disease.