The association of a codon 136 PrP gene variant with the occurrence of natural scrapie

Incidence of both experimental and natural scrapie in sheep has been associated with polymorphisms of the PrP gene. In case/ control studies the PrP allele which encodes valine at codon 136 (Val₁₃₆) is found in 96-100% of naturally infected scrapie sheep of Shetland, Scottish Halfbred and Bleu du Maine breeds. In contrast, in healthy animals from the same flocks, the most frequent allele encodes Ala₁₃₆ (91-100% of sheep). However Val₁₃₆ does not correlate with incidence of scrapie in two other flocks - Poll Dorsets and Suffolks - and there may therefore be breed differences in PrP genotypes affected by scrapie.