In view of the central role of the host-encoded proteins such as PrP in TSEs, amyloid precursor protein (APP) in AD and microtubule associated protein (tau) in AD, PD and tauopathies, these neurodegenerative diseases are grouped together as protein misfolding diseases [20,21,29,170,171,172,173,174,175,176,177,178]. This evidence concerns the gene PRNP and Alzheimer disease.