Prion protein (PRNP) gene polymorphisms analysis and susceptibility to scrapie of native sheep breeds from North-Eastern Italy

Prion protein (PRNP) gene polymorphisms are responsible for susceptibility to Scrapie, a transmissible spongiform encephalopathy affecting sheep and goats. As a result, different genotypes were defined based on the combination of polymorphic codons and their classification into risk groups of susceptibility (R1-R5) was proposed to plan the use of animals for reproductive purposes. Breeding programmes aimed at increasing the frequency of the ARR resistant allele in sheep population and to progressively eradicate PRNP susceptible alleles. In this study the relative frequency of PRNP haplotypes and genotypes were investigated in twelve local sheep breeds, some of them endangered, from three different Italian geographical areas: Alpagota, Brogna, Foza and Lamon from Veneto region, Carsolina and Plezzana from Friuli Venezia Giulia region, and Tiroler Steinschaf, Juraschaf, Tiroler Bergschaf, Schnalser Bergschaf, Schwarz-braunes Bergschaf and Villnoesser Brillenschaf from the Autonomous Province of Bolzano. All six known PRNP gene alleles were observed in the total sheep population analyzed and most of the animals carried genotypes with moderate to very high susceptibility to classical Scrapie. The predominant allele in all breeds was ARQ, with frequencies over 60% in some breeds (Foza, 63%, Alpagota, 63.9%, Tiroler Steinschaf, 68.4%). The ARR and VRQ alleles showed variable frequencies depending on the sheep breed with mean values of 27% and 6% respectively. The worst situation was observed in the Lamon breed with about 37.5% of the analysed animals carrying the VRQ risk allele, followed by Villnoesser Brillenschaf and Schnalser Bergschaf breeds with approximately 18% and 14.2% of the animals assigned to the high risk classes respectively. The different frequencies of the susceptible VRQ allele may depend both on the geographical isolation and the reproductive practices of the breeders. In addition, the presence of the ARK allele was demonstrated in eight breeds analysed, with a particularly significant frequency in the Foza and Tiroler Bergschaf breeds (6.8% and 5.7% respectively) compared to what is reported in literature. This study highlights the importance of PRNP gene genotyping of different sheep breeds in order to evaluate, guide and improve the organization of possible selection strategies that could lead to an improvement in resistance to Scrapie while preserving the genetic and cultural heritage of these autochthonous sheep populations.