HTT and Huntington disease: Huntington’s disease (HD) is an autosomal dominant and fatal neurological disorder caused by the loss of GABAergic inhibitory spiny projection neurons in the striatum due to the abnormal triplet expansion of a CAG repeat in exon-1 of the gene responsible for HD that results in elongated polyglutamine stretches in the protein product known as mutant huntingtin (Htt) [88,89,90,91].