Huntington’s disease (HD) is an autosomal-dominant hereditary neurodegenerative disorder caused by a pathogenic expansion of the CAG trinucleotide repeats in exon 1 of the huntingtin (HTT) gene (A novel gene containing a trinucleotide repeat that is expanded and unstable on Huntington’s disease chromosomes. The gene discussed is HTT; the disease is juvenile Huntington disease.