PRNP and prion disease: Prion diseases are infectious brain proteinopathies caused by a pathogenic form of prion protein (PrPSc) converted from an endogenous form of prion protein (PrPC) and are classified into several types in a wide range of mammalian hosts: Creutzfeldt–Jakob disease (CJD), fatal familial insomnia (FFI) and Gerstmann-Sträussler-Scheinker syndrome (GSS) in humans; scrapie in sheep and goats; bovine spongiform encephalopathy (BSE) in cattle; and chronic wasting disease (CWD) in the Cervidae family (1–7).