HTT and Alzheimer disease: For example, Alzheimer’s disease (AD) is defined by the accumulation of extracellular amyloid-β (Aβ) peptides and hyperphosphorylated tau protein that form neurofibrillary tangles (NFTs) inside neurons [1,2], Parkinson’s disease (PD) is characterized by the presence of α-synuclein fibrils that form Lewy bodies [3], and Huntington’s disease (as well as eight additional polyglutamine disorders) is associated with aggregation of the Huntingtin protein due to expansion of a polyglutamine tract within its N-terminal region [4].