Genetic variability in the prion protein gene in five indigenous Turkish sheep breeds

Abstract

Ovine susceptibility to scrapie is largely controlled by polymorphisms in the PRNP gene. Beginning in 2003, breeding programmes based on the known association between this gene and the susceptibility/resistance status of this disease have been implemented in many European countries. This is not the case in Turkey, where the PRNP gene was not genotyped in native sheep breeds until recently. We sequenced the complete open reading frame of the PRNP gene in 100 sheep belonging to five native Turkish sheep breeds (Akkaraman=21; Morkaraman=20; Tuj=17; Hemsin=23; Karayaka=19). Based on the variability found at codons 136, 154 and 171 (also referred to as standard codons), we determined six alleles VRQ, TRQ, ARR, ARH, ARK and ARQ. The archetype, ARQ, was the most frequent variant in each of the five breeds (across-breed frequency=0.710), while the second most frequent was the resistance-associated ARR allele (0.140). The susceptible VRQ allele exhibited the lowest frequency (0.015). The AHQ allele was not found in any of the analysed breeds. Beyond variability in the standard codons, we found ten additional amino acid variants (M112T, G127S, G127V, M137T, L141F, H143R, N146S, Y172D, Q189L and V213E), one of which, V213E, has not been previously described to our knowledge. Overall, this report may serve as a complement of previous studies on the genetic background of native Turkish sheep regarding the resistance/susceptibility status to classical and atypical scrapie.