CACNA1A and Huntington disease: A distinct group within inherited neurodegenerative diseases comprise the so-called polyglutamine (polyQ) disorders, which include the following nine conditions: spinobulbar muscular atrophy (SBMA), dentatorubral-pallidoluysian atrophy (DRPLA), Huntington's disease (HD), and six spinocerebellar ataxias (SCA1, SCA2, SCA3, SCA6, SCA7, and SCA17).