PRNP and human prion disease: Prions, the infectious agents associated with transmissible spongiform encephalopathies such as scrapie in sheep, chronic wasting disease (CWD) in deer and elk, bovine spongiform encephalopathy (BSE), and Creutzfeldt-Jakob disease (CJD) in humans, are primarily comprised of PrPSc, a protease-resistant misfolded isoform of the cellular prion protein PrPC[1].