HTT and Huntington disease: HTT misfolding and aggregation disrupt many cellular processes, and there is substantial evidence to suggest that mHTT oligomers and/or insoluble fibrils directly cause neurodegeneration in HD (Takahashi et al., 2008; Lajoie and Snapp, 2010; Leitman et al., 2013; Ramdzan et al., 2017).