PRNP and scrapie: We have studied the distribution of scrapie infectivity and Abnormal PrP in 4 ARQ/ARQ sheep naturally affected with scrapie with a neuropathological phenotype indistinguishable from other scrapie cases in sheep of the same genotype from different European countries [13]; these previous studies have reported the tissue distribution of PrPSc by IHC but have limited biochemical and bioassay data [16,14,32].