PRNP and scrapie: Prions formed by mammalian prion protein (PrP) cause Creutzfeldt–Jakob disease (CJD), Gerstmann–Sträussler–Scheinker syndrome, fatal familial insomnia, and kuru in humans, scrapie in sheep, bovine spongiform encephalopathy (BSE) in cattle and chronic wasting disease in cervids (Prusiner, 1998; Shorter and Lindquist, 2005).