Prion diseases, such as Creutzfeldt-Jakob disease (CJD) in humans, bovine spongiform encephalopathy (BSE), and chronic wasting disease (CWD) in cervids, are invariably fatal neurodegenerative disorders caused by the accumulation of misprocessed prion protein (PrPSc) in the brain. The gene discussed is PRNP; the disease is prion disease.