PRNP and prion disease: Conformational conversion of the cellular isoform of prion protein, designated PrPC, into its abnormally folded, amyloidogenic isoform PrPSc, is a key pathogenic event in prion diseases, or transmissible spongiform encephalopathies, a group of fatal neurodegenerative disorders including Creutzfeldt-Jakob disease (CJD) in humans and scrapie and bovine spongiform encephalopathy (BSE) in animals [1–3].