PRNP and fatal familial insomnia: About 15% of human TSEs are linked to various mutations in the PRNP gene encoding PrPC [9], leading to Creutzfieldt–Jacob disease, (CJD), Gerstmann–Straussler–Scheinker disease (GSS) or fatal familial insomnia (FFI), whereas the majority are sporadic (sporadic CJD and sporadic FFI) and a few are transmitted either iatrogenically (iCJD) or through the consumption of infected tissue (kuru, new variant CJD (nvCJD)) [10].