The pathological hallmark of each ND contains an abnormal aggregation of different proteins: amyloid-β (Aβ) and tau in AD, α-synuclein in PD, huntingtin in HD, and several proteins including Tar DNA-binding protein of 43 kDa (TDP-43) and mutant superoxide dismutase 1 (SOD1) in ALS [8]. Here, HTT is linked to Alzheimer disease.