Analysis of polymorphic PRNP microsatellite and ORF sites in German sheep breeds.

Polymorphic microsatellite and open-reading frame (ORF) sites in the prion protein coding gene (PRNP) were analysed in eight sheep breeds. The three microsatellite sites S11, S15 and S24 were genotyped by fragment length analysis, and the ORF codons 136, 154 and 171 were analysed after direct sequencing. Unexpected polymerase chain reaction (PCR) products of microsatellite sites and ORF haplotypes with more than one heterozygous site were submitted to cloning and then sequenced. The microsatellite sites were polymorphic in all breeds with two to five alleles per site. On average of breeds and sites, the microsatellites had higher degrees of polymorphism than the ORF sites. The ARR/ARR ORF genotype occurred always together with the microsatellite genotypes S11 152/152, S15 179/179 and S24 144/144. As ORF and microsatellite alleles of the PRNP were observed in typical combinations, the microsatellite genotypes were significantly associated with scrapie incidences or risk classes based on the ORF genotypes. The microsatellite sites were highly polymorphic and therefore are advantageous markers for evaluation of scrapie disposition and fine mapping of effects on scrapie pathogenesis within the gene.