Misfolding of the cellular prion protein, PrPC,into the amyloidogenic isoform, PrPSc, which forms infectiousprotein aggregates, the so-called prions, is a key pathogenic event in prion diseases.No pathogens other than prions have been identified to induce misfolding ofPrPC into PrPSc and propagateinfectious prions in infected cells. This evidence concerns the gene PRNP and prion disease.