PRNP and fatal familial insomnia: In humans, prion diseases can be sporadic, acquired or genetic, linked to mutations in the gene encoding prion protein, PRNP. In the globular domain over 20 different mutations in PRNP have been associated with familial forms of prion disease, familial Creutzfeldt-Jakob disease (fCJD), Gerstmann-Sträussler-Scheinker syndrome (GSS), and fatal familial insomnia (FFI) [2].