A survey of scrapie PrP genotype results and their relationship with coat colour and hornedness in selected UK rare breed sheep

Abstract

Scrapie is a transmissible spongiform encephalopathy (TSE) and belongs to a category of incurable diseases that include BSE in cattle. An association exists between the Prion-Protein (PrP) genotype of an animal and the risk of developing disease after exposure (Tongue et al., 2004). This PrP genetic information is the basis of the National Scrapie Plan (NSP) which aims, through genotyping, to eradicate those individuals which have the susceptible alleles. Studies into scrapie risk (Jeffrey et al., 2002) have highlighted several alleles which confer scrapie susceptibility. The NSP have used these alleles to categorise individuals according to risk with group one being most scrapie resistant to group five being least resistant. VRQ alleles are synonymous with infection however the ARQ affords susceptibility but not the disease itself. Genotype may however not be the sole indicator of scrapie risk. There is an inference of a relationship between phenotypic characteristics (hornedness, coat colour) and scrapie risk. These alternative indicators of scrapie risk may affect the final choice of susceptible individuals. Scrapie risk studies carried out on the Shetland Isles (Jeffrey et al., 2002) investigated the alleles concerned with scrapie infection. Results confirmed that VRQ alleles are synonymous with scrapie infection however the ARQ alleles, even though they afford susceptibility, do not necessarily confer disease, the animal still has to be exposed to the scrapie agent. Using survey-type questionnaires, the study investigated any potential relationship between the PrP gene, coat colour and hornedness.