Prion diseases, or transmissible spongiform encephalopathies (TSEs), are a class of untreatable fatal neurodegenerative disorders caused by the accumulation and aggregation in the central nervous system of misfolded conformers (scrapie prion protein: PrPSc) of the host-encoded membrane-anchored prion protein (cellular prion protein: PrPC). The gene discussed is PRNP; the disease is prion disease.