HTT and Alzheimer disease: This process appears to be a common feature of most neurodegenerative diseases where specific cellular proteins—huntingtin protein in Huntington’s disease, α-synuclein in Parkinson’s disease, and β-amyloid (Aβ) and hyperphosphorylated tau in Alzheimer’s disease (AD)—misfold, nucleate, and spread in an infectious manner that is described as “prion-like” (2, 4, 5).