HTT and Parkinson disease: For example, in Alzheimer’s disease (AD), amyloid β (Aβ) and Tau protein aggregates are prominent (Baker et al., 1994, Braak and Braak, 1991); in Parkinson’s disease (PD), α-synuclein (α-syn) aggregates are prevalent (Braak et al., 2003, Del Tredici et al., 2002); TAR DNA-binding protein 43, superoxide dismutase 1, and fused in sarcoma aggregates have been implicated in amyotrophic lateral sclerosis (ALS) (Shaw and Eggett, 2000); and in Huntington’s disease (HD), mutant huntingtin has been identified (Graveland et al., 1985).