PRNP and prion disease: Also, addressing (1) the mechanism of the conversion of the hereditary prion disease-associated mutated PrPs into PrPSc, (2) the molecular nature of neurotoxic and infectious PrPSc molecules, and (3) the mechanism of how the N-terminal polybasic region and the central residues 91–106 are involved in the conversion of PrPC into PrPSc is important not only for further understanding of the pathogenic mechanisms of prion diseases, but also for the development of effective treatment and prevention measures for prion diseases.