PRNP and prion disease: Prion diseases or transmissible spongiform encephalopathies, including Creutzfeldt Jakob Disease (CJD), are fatal neurodegenerative disorders characterized by extracellular accumulation of the scrapie form of the prion protein (PrPSc), a pathological isoform of the normal cellular prion protein (PrP) resulting in rapidly progressing neuronal loss.