PRNP and Alzheimer disease: Although, there are no specific toxic proteins that are exclusive of any particular ND, several may be present in different NDs [25,41]; for example, amyloid-beta (Aβ) and hyperphosphorylated-Tau (p-Tau) have been described as accumulating in AD, alpha-synuclein (α-syn) in PD, transactive response DNA binding protein 43 (TDP-43) in FTLD and ALS, huntingtin protein (HTT) in HD, and prion proteins (PrP) in PRD [25,41].