Prion diseases, or transmissible spongiform encephalopathies, including Creutzfeldt-Jakob disease (CJD), Gerstmann–Sträussler–Scheinker syndrome (GSS), and fatal familial insomnia (FFI) in human, bovine spongiform encephalopathy (BSE) in cattle, scrapie in sheep and goats, are neurodegenerative disorders characterized by the accumulation of misfolded prion protein (PrP), an abnormal isoform of PrP (PrPSc), in the central nervous system [50,51,52,53]. Here, PRNP is linked to fatal familial insomnia.