HTT and juvenile Huntington disease: Mutant huntingtin (mHtt) undergoes cleavage to release an N-terminal fragment containing the polyglutamine region (Becher et al, 1998; Thomas et al, 1998; Landles et al, 2010), and this fragment forms inclusions in individuals affected by Huntington’s disease (Scherzinger et al, 1997; Huang et al, 1998; McGowan et al, 2000).