With an estimated prevalence of 1–15 cases per 100,000 inhabitants [1], Huntington’s disease (HD) (OMIM #143100) is a monogenic neurodegenerative disorder that similarly affects both sexes and is caused by an abnormal expansion of CAG repeats in the first exon of the Huntingtin (HTT) gene. The gene discussed is HTT; the disease is juvenile Huntington disease.