On the other hand, mutations in the normal prion protein encoded by the PRioN Protein (PRNP) gene, are linked to genetically inherited prion diseases including Gerstmann-Strausler-Sheinker (GSS) disease, fatal familial insomnia (FFI) and genetically associated CJD [2, 4]. The gene discussed is PRNP; the disease is fatal familial insomnia.