PRNP and fatal familial insomnia: This same phenomenon was first observed for the prion protein (PrP), which misfolds from the cellular conformation (PrPC) into the pathogenic conformation (PrPSc) in fatal neurodegenerative diseases including Creutzfeldt-Jakob disease (CJD), Gerstmann-Straussler-Scheinker disease, and fatal familial insomnia.