Given the likely key pathogenic role of a partially protease-resistant misfolded form of PrPC (PrPSc), and the critical requirement for PrPC, in transmissible spongiform encephalopathies [8,97], the relationship and commonalities between prion-mediated neurodegenerative diseases and AD have become a major focus of research [98-104]. This evidence concerns the gene PRNP and neurodegenerative disease.