PRNP and prion disease: The molecular pathogenesis of PrP prion diseases is based on the conversion of the hosts’ normal monomeric prion protein (PrPC) into a refolded, aggregated, and infectious state (generically called PrPSc) in which, for the prion structures that have been solved to date, PrP molecules become stacked via parallel in-register intermolecular β-sheets (PIRIBS) into amyloid fibrils [11–13].