PRNP and fatal familial insomnia: Human prion diseases include (I) iatrogenic forms, e.g., Kuru, iatrogenic Creutzfeldt–Jakob disease (iCJD) and variant CJD; (II) sporadic forms, e.g., sporadic CJD and fatal insomnia (sFI); and (III) familial forms carrying point or insertional mutations in the PRNP gene encoding PrPC, such as genetic CJD, fatal familial insomnia (FFI) and Gerstmann–Straussler–Scheinker (GSS) syndrome [2,3].