Finally, it is worth noting from the disease model point of view that over-expression of only the first exon of the HTT gene is sufficient to phenocopy most of the HD pathogenesis and toxicity both in cell-based and animal model systems (DiFiglia et al., 1995; Gunawardena et al., 2003; Gauthier et al., 2004; Lee et al., 2004; Menzies et al., 2017; Pandey et al., 2018; Masnata et al., 2019; Tao et al., 2019). The gene discussed is HTT; the disease is Huntington disease.