To date, nine polyQ diseases have been described: Huntington’s disease (HD), X-linked spinobulbar muscular atrophy (Kennedy disease), spinocerebellar ataxia (SCA) 1, SCA2, SCA3 (also known as Machado–Joseph disease), SCA6, SCA7, SCA17, and dentatorubral pallidoluysian atrophy [276]. Here, CACNA1A is linked to Huntington disease.