HTT and Huntington disease: Huntington’s disease (HD) is a neurodegenerative disorder with an autosomal dominant trait and is caused by unusual expansion of CAG DNA triplet repeats in exon 1 of the IT15 gene, which is translated to an expanded polyglutamine (polyQ) repeat in huntingtin (HTT), a 350-kDa protein whose function remains to be fully investigated (MacDonald et al., 1993; Saudou and Humbert, 2016).