PRNP and fatal familial insomnia: All subtypes of prion disease, including Creutzfeldt-Jakob disease (CJD), fatal familial insomnia (FFI), Kuru, and Gerstmann-Sträussler-Scheinker (GSS) disease in humans as well as scrapie, chronic wasting disease, and bovine spongiform encephalopathy (or mad cow disease) in animals, are caused by PrP (1).