HTT and Alzheimer disease: In neurodegenerative disorders, such as AD, PD, HD, ALS and prion protein disease, several misfolded proteins are observed, such as neurotoxic oligomers of the amyloid β-peptides (Aβ) and Tau in AD, α-synuclein in PD, a polyglutamine (polyQ) extended huntingtin in HD, superoxide dismutase (SOD1), Tar-DNA binding protein (TDP-43) and fused in sarcoma (FUS) in ALS, and prion protein (PrP) in prion diseases.