Prion diseases, such as bovine spongiform encephalopathy (BSE) in cattle, scrapie in sheep, and Creutzfeldt-Jakob disease (CJD) in humans, are fatal, transmissible, neurodegenerative disorders associated with the aggregation of an infectivity-associated isoform (PrPSc) of the cellular prion protein (PrP) (1). The gene discussed is PRNP; the disease is prion disease.