HTT and Alzheimer disease: Importantly, each neurodegenerative disease has typical aggregating proteins, such as amyloid β (Aβ) in AD, tau in AD and FTD, α-synuclein in PD, TAR DNA-binding protein 43 (TDP-43) in ALS and FTD, and mutant huntingtin in HD (Winklhofer et al., 2008).