PRNP and prion disease: It has been well-documented that the co-existence of PrPC and PK-resistant PrPSc (rPrPSc) is a prerequisite for the pathogenesis of various prion diseases; however, what type of PrPSc conformers are directly responsible for the PrP deposition in the brain and the neuropathological changes in the prion diseases remains poorly understood [11].