Many hypotheses have been proposed (McLaughlin et al., 1996; Zuccato et al., 2003; Cornett et al., 2005; Atwal et al., 2007; Rockabrand et al., 2007; Chow et al., 2012; Nalavade et al., 2013; Yano et al., 2014) (a partial list) that can explain different groupings of the nine experimental observations of HD pathogenesis and Htt behavior we list above. This evidence concerns the gene HTT and Huntington disease.