Polymorphism at codons 136, 141 and 154 in the ovine prion protein gene in the state of Xinjiang

Abstract

Scrapie is a fatal and infectious neurodegenerating disease. The polymorphism in the prion protein (PRNP) gene is linked to the development of clinical signs of scrapie. The most important polymorphism appears to be at codons at 136(V/A), 154(H/R), and 171(H/Q/R). In this study, we investigated the polymorphisms at these codons in 746 individuals among ten sheep breeds (i.e., ALeTai, BaShiBai, BaYinBuLuKe, Celehei, DuoLang, He Tian, Chinese Merino, German Merino, Texel, and Suffolk sheep) in Xinjiang in order to evaluate the relative susceptibility of sheep to scrapie. A total of 8 alleles (i.e., ARQ, ARR, ARH, ARK, VRQ, AHR, AHQ and AHH) were observed. The alleles ARQ and ARR were found in all of the breeds with the highest frequency for allele ARQ. Allele ARH was found in eight breeds except for Suffolk and German Merino, while the ARK was only identified in ALeTai, BaShiBai, BaYinBuLuKe, and DuoLang native sheeps. The alleles VRQ, AHR, AHQ and AHH were detected exclusively in Chinese Merino with extremely low frequencies. Moreover, the genotypes contained by the eight alleles were also determined subsequently. A total of thirteen genotypes, such as ARQ/ARQ, ARQ/ARK, ARR/ARR, ARH/ARH, ARQ/ARR, ARH/ARQ, ARH/ARR, ARK/ARK, ARH/ARK, ARQ/VRQ, ARQ/AHQ, ARQ/AHR and ARH/AHH were detected. The genotype ARQ/ARQ with moderate susceptibility was found with the highest frequency among the ten breeds, whereas the genotype ARR/ARR with highest resistance to scrapie was merely identified in BaYinBuLuKe, Celehei, Chinese Merino, Texel and German Merino sheep, which had very low frequencies. In addition, the genotype VRQ/ARQ with high susceptibility was first variant reported in Chinese Merino sheep. Our data, therefore, indicate that the general genetic resistance of dominating sheep breeds in Xinjiang to scrapie was considerably low.