Due to selective neuronal vulnerability, pathological CAG expansion on the HTT gene (hereafter also referred to as HD mutation) results in extensive loss of striatal medium spiny neurons and cortical neurons, a disease hallmark evident in postmortem HD patient brains (Aylward et al., 2011; Halliday et al., 1998; Ross and Tabrizi, 2011). This evidence concerns the gene HTT and Huntington disease.