PrP genotypes in scrapie-affected sheep in Greece—The contribution of the AHQ 1 polymorphism

In this study, brain tissues from 337 scrapie-affected sheep (158 confirmed as Chios crossbred scrapie-affected sheep and 179 as unconfirmed scrapie-affected sheep) as well as blood samples obtained from a total of 348 Chios healthy sheep with pedigree from the flock of the National Agricultural Research Foundation—Veterinary Research Institute of Thessaloniki, have been fully genotyped. The aim of this work was to study the contribution of the sheep PrPn polymorphisms and especially those, with histidine in codon 154, so as to correlate AHQ haplotype with scrapie susceptibility in Greek Chios crossbred sheep. To detect polymorphisms in sheep PrPn, a Restriction Fragment Length Polymorphism (RFLP) as well as a micro-array method were used (Homogenous Mass Extend Assay—SEQUENOM, Genaissance). A total of 10 different genotypes were found. Genotype of high risk ARQ/ARQ appeared at high frequency up to 70.39% in unconfirmed scrapie-affected sheep while it was lower, up to 68.35%, in Chios crossbred scrapie-affected sheep. Moreover in the Chios crossbred scrapie-affected sheep, the histidine in codon 154 was appeared at a surprisingly high frequency, up to 13.61%. The same allele in Chios healthy sheep was up to 1.70%. In the Chios crossbred scrapie-affected sheep, genotypes with histidine (H) in codon 154 were found at significant high frequencies: ARQ/AHQ at 24.51%, AHQ/ARH at 1.90% and AHQ/AHQ at 0.63%, a total of 27.04%. In Chios healthy sheep the ARQ/AHQ-genotype was found at 2.30%. This indicates that probably AHQ haplotype favours scrapie infection of AHQ Chios crossbred carriers. Therefore, it remains to be clarified whether the PrP haplotype classification for Greek sheep breeds is the same or differs from the classification of the British National Scrapie Plan.