All forms of prion diseases, including Creutzfeldt–Jakob disease (CJD), fatal familial insomnia, and Gerstmann–Sträussler–Scheinker syndrome, are associated with the conformational conversion of the cellular prion protein (PrP), a cell surface glycoprotein mainly expressed in the central nervous system, into a misfolded isoform (PrPSc) that accumulates in the brain of affected individuals.19 Here, PRNP is linked to fatal familial insomnia.