In HD, the pathological expansion of CAG trinucleotide repeat encoding a polyglutamine (polyQ) tract in the amino-terminal region of the Huntingtin protein results in an abnormal polyglutamine stretch and in accumulation of polyQ-expanded HTT (Mattson et al., 2008; Song et al., 2011; Martin et al., 2015). This evidence concerns the gene HTT and Huntington disease.