HTT and Alzheimer disease: Although clinically and etiologically very diverse, a common characteristic between many neurodegenerative diseases is their causal association with protein misfolding and the aggregation of the respective proteins, such as α-synuclein in Parkinson’s disease (PD), β-amyloid, and tau in Alzheimer’s disease (AD), and huntingtin in Huntington’s diseases (HD), which leads to an impaired protein homeostasis [28].