PRNP and scrapie: This hypothesis is extrapolated from studies in scrapie-affected PRNP heterozygous sheep demonstrating that although expression of the host cellular form of the prion protein (PrPC) is equal for each PRNP allele, conversion of PrPC to the disease-associated form (PrPSc) is more efficient for the PrPC moiety that confers a greater susceptibility to disease20,21.