HTT and Huntington disease: Proteolysis of mHtt results in the formation of different mHtt protein fragments of which the N-terminal exon1 fragment containing the polyQ expansion was found to be the most pathogenic and is also observed in fibrillar aggregates in brains of HD patients (DiFiglia et al., 1997; Schilling et al., 2007; Landles et al., 2010) and overexpression of mutant Htt exon1 results in HD-like symptoms in mice (Mangiarini et al., 1996).