HTT and Huntington disease: Genetic studies show that knockout of Htt induces certain HD phenotypes and overexpression of wild-type Htt rescues these phenotypes (Cattaneo et al., 2005; Gauthier et al., 2004), implying that dominant negative effects of mHtt on the wild type protein might contribute to the disease state (Ho et al., 2001; Nasir et al., 1995; Zeitlin et al., 1995).