PRNP and human prion disease: Transmissible spongiform encephalopathies (TSE) such as scrapie in sheep and goats, bovine spongiform encephalopathy (BSE) in cattle and Creutzfeldt-Jakob disease (CJD) in humans, are associated with the accumulation of an abnormal, host-encoded, prion protein (PrP) in infected tissues [1].