Polymorphisms of the prion protein gene Arabi sheep breed in Iran

Ovine scrapie is a neurodegenerative disease caused by polymorphisms of the prion protein gene (Prnp); especially the amino acid residue alterations at codons 136, 154, and 174, in sheep have been found to be associated with susceptibility to scrapie disease. We studied Prnp polymorphisms in local sheep of Khuzestan, Iran. In this study, a total of 250 healthy and randomly chosen sheep were investigated. Information from the breeder was considered in order to avoid family connections. The genetic DNA of blood samples was extracted, amplified and sequenced. At codon 136, are two different amino acid residues A and V with frequencies of 98.8 and 1.2%, respectively. In our study, the amino acid residue at 154 in all the prion protein (PrPs) was A. At codon 171, are three different amino acid residues Q, R and H with frequencies of 68.4, 21.8 and 9.8%, respectively. The frequency of the amino acid residues ARQ/ARQ at codons 136, 154, and 171, respectively, which is associated with medium-high susceptibility to scrapie, was 43.2%. The frequencies of genotypes ARQ/ARR, ARQ/ARH, ARQ/VRQ, ARR/ARH and ARH/ARH were 38, 10, 1.2, 5.2 and 2.4, respectively. The scrapie-resistant genotype ARR/ARR was not found. Also, the highly susceptible genotype VRQ/VRQ at these codons were not detected in the tested sheep. In addition, five polymorphism were identified (G127V, N146S, Y172D, S173N, and V179E) at different codons of PrP gene.