Association between natural scrapie and PrP genotype in a flock of Suffolk sheep in Scotland

Abstract

The incidence of natural scrapie in sheep is associated with polymorphisms of the PrP gene, particularly those at codons 136, 154 and 171. In many breeds, the PrP allele encoding valine at codon 136 confers an extremely high risk of scrapie, but in Suffolk sheep this allele is vanishingly rare. In this study of a single closed flock of Suffolk sheep in Scotland, scrapie occurred primarily in animals which were homozygous for glutamine at codon 171, a genotype which was significantly less frequent in healthy flockmates. However, the apparent linkage between glutamine at codon 171 and scrapie was not completely recessive because two of 64 scrapie cases were heterozygous glutamine/arginine. These results suggest that breeding for increased resistance to scrapie in Suffolks by the selection of animals according to their PrP genotype is a feasible option.

Evidence for protein X binding to a discontinuous epitope on the cellular prion protein during scrapie prion propagation

“…In sheep, the substitution of a basic residue at position 171 probably prevents scrapie through a dominant-negative mechanism similar to that postulated for a basic residue at 219 protecting humans from CJD. With few exceptions, only sheep that are Q͞Q at 171 develop scrapie; sheep that are Q͞R or R͞R are resistant (31)(32)(33)(34)(35)(36)(37)(38)(39). These findings suggest that R171 creates a PrP C molecule in sheep that acts as a dominant negative in preventing PrP Sc formation (Fig.…”

The evidence of associations between prion protein genotype and production, reproduction, and health traits in sheep

“…Further concerns that PrP genotype could be associated with muscularity were raised following the observation that a line of sheep that was selected for increased lean tissue growth rate had a much higher rate of scrapie than an unselected control line [45]. The selection line had a higher frequency of QQ171 animals than the control line.…”

“…It therefore was possible that this reflected a genetic association between scrapie susceptibility and lean tissue growth rate. However, as the study was not designed to test this hypothesis it was suggested [45] that the association might simply have been a consequence of founder effects on gene frequency at the PrP locus. The evidence from studies that involved evaluation of conformation and related measures such as muscle and fat depth are summarised in Table III, while carcass composition data are summarised in Table IV.…”

Application of Temperature-Gradient Gel Electrophoresis for Detection of Prion Protein Gene Polymorphisms in Polish Świniarka Sheep

“…9 The results of this study indicate that the dominant alleles in Świniarka sheep are ARR and ARQ. These PrP alleles are also frequently present in Romanov sheep, 4 Suffolk sheep 8,11 and Valachian sheep. 14 The ARR allele is associated with high resistance to scrapie, so high frequency of this allele in some breeds of sheep can be exploited to increase the genetic resistance to scrapie of sheep flocks through introduction of selective breeding programs.…”

“…Analysis of sheep belonging to the Świniarka breed also revealed the presence of the VRQ allele, which is associated with high susceptibility to scrapie. This allele is very rare or absent in some sheep breeds, like Berichone du Cher, 5 Masses, 10 and Suffolk, 8,11 but highly frequent in Icelandic sheep (about 80%) and in Norwegian Rygja sheep (48%). 2 There is no data on PrP genotypes of Świniarka sheep in currently available literature, probably because this breed of sheep can be found only in the southern and southeastern part of Europe.…”