HTT and Alzheimer disease: According to the affected protein pathology Alzheimer’s disease (AD) is associated with accumulation of amyloid-β and hyperphosphorylated tau, the Parkinson’s disease (PD) is associated with α-synuclein aggregates in Lewy bodies, the amyotrophic lateral sclerosis (ALS) is associated with TDP-43 or SOD1 protein dysfunction and Huntington’s disease (HD) is associated with mutant huntingtin protein due to CAG triplet repeat expansion [4].