Prion protein (PrP) gene polymorphisms associated with natural scrapie cases and their flock-mates in Ireland

The PrP genotypes associated with natural scrapie in Ireland were determined and a comparison was made between genotypes found in scrapie-infected sheep and those found in healthy animals from scrapie-infected flocks. Seven PrP genotypes were identified in scrapie-infected animals: VV 136 RR 154 QQ 171, VA 136 RR 154 QQ 171, VA 136 RR 154 QR 171, VA 136 RR 154 QH 171, AA 136 RR 154 QQ 171, AA 136 RR 154 QH 171 and AA 136RR 154HH 171. Of 11 scrapie-infected flocks, 15 genotypes were identified in the healthy flock-mates. The genotypes identified in scrapie-affected animals were also all identified in healthy flock-mates. In 9 of the 11 flocks studied, the genotype frequencies among scrapie-infected animals were significantly different from those among healthy flock-mates. The results show that there is a significant risk of developing the clinical signs of scrapie associated with particular PrP genotypes in the Irish sheep population. The association between the V 136R 154Q 171 allele and scrapie was evident, as was the association between A 136R 154R 171 and resistance to developing the clinical signs of scrapie. The presence of the A 136H 154Q 171 allele in the flocks examined resulted in a decreased risk of developing scrapie compared to the presence of the A 136R 154Q 171.