HTT and Huntington disease: N-terminal fragments of Htt have been found in nuclear inclusion bodies in HD patients (12), and overexpression of exon 1 of Htt (Httex1) with expanded polyQ repeats alone is sufficient to a variable extent recapitulate many characteristics of HD in mice (13), suggesting that N-terminal Htt fragments may play a critical role in the pathogenesis of HD (14, 15).