Prion protein polymorphisms in autochthonous European sheep breeds in respect to scrapie eradication in affected flocks

Resistance or susceptibility of sheep to scrapie is influenced by polymorphisms in the prion protein (PrP) gene (PRNP). Consequently, scrapie eradication in affected sheep flocks within the European Community (EC) aims at quickly removing the highly susceptible haplotype for classical scrapie, V136R154Q171 (VRQ), and increasing the number of sheep with the most resistant genotype for classical scrapie, ARR/ARR. In total, 1672 blood samples of 56 sheep breeds originating from 15 European and Middle Eastern countries were analyzed for nucleotide polymorphisms at codons 136, 154 and 171 of PRNP using improved restriction-fragment-length-polymorphism analyses. The frequency of the genotype ARR/ARR ranged from 0 to 42%. This genotype was absent in the samples from 11 breeds. Genotypes with at least one VRQ haplotype but no ARR haplotype showed frequencies from 0 to 21%. Such genotypes were not found in 34 of the 56 investigated breeds. The observed differences in the frequencies of PrP haplotypes and genotypes would have different consequences regarding culling of sheep in respect to genetically based scrapie eradication in affected flocks of these breeds.Furthermore, the rare ARK haplotype has been described for the first time in the Italian Bergamasca breed.