HTT and Huntington disease: On the other hand, Huntington's disease (HD) is an autosomal–dominant inherited neurological disorder caused by an unstable trinucleotide CAG repeat expansion at the N-terminus of the IT-15 gene, encoding the ~350 kDa huntingtin protein (Htt) (Jimenez-Sanchez et al., 2017; Tabrizi et al., 2020).