HTT and juvenile Huntington disease: Huntington’s disease (HD), an autosomal dominant monogenic neurodegenerative disease, was first described in 1872 by George Huntington, who reported an inherited choreiform disorder [1] resulting from the expansion of cytosine, adenine, and guanine (CAG) tract in the IT15 gene (Huntingtin gene, HTT), located in the region 4p16.3.