PRNP and fatal familial insomnia: Accumulation of prion protein (PrP) amyloids in the brain causes fatal degenerative disorders such as Gerstmann–Straussler–Scheinker disease (GSS), prion protein cerebral amyloid angiopathy (PrP-CAA), scrapie of sheep and goat, spongiform encephalopathy of cattle, kuru, Creutzfeldt–Jakob disease (CJD), and fatal familial insomnia (FFI).