PRNP and Creutzfeldt Jacob disease: APrP – Prion diseases are caused by misfolding and aggregation of the prion protein (PrP) which manifests as different diseases including Creutzfeldt-Jakob disease (CJD) and hereditary diseases such as fatal familial insomnia (FFI) and Gerstmann – Sträussler – Scheinker syndrome (GSS).