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Ovine PrP gene sequences from sheep with complex genotypes - SE0245

Description
The ability to eradicate scrapie from the British sheep population is fundamentally based on the genetics of the PrP gene. PrP genotyping for the main three codons 136, 154 and 171 has become a standard applied to most breeds. The sale and breeding of sheep is depending increasingly on certification of the scrapie risk group, which is based on PrP genotype. Within the National Scrapie Plan, every animal tested is expected to be classified in this risk assessment scheme. There are a small number of animals with atypical (also called complex) genotypes where the risk certification is difficult and further evaluation of these genotypes is required.

Preliminary studies of NSP complex genotypes suggest that they can be divided into two groups: those with a true biological basis and those known as “false” or “technical” complex, which may be the result of artefacts caused by additional mutations in the gene sequence. Presently it is unclear what proportion of complex results are biological and what proportion are “false”. A technical origin has already been established for some atypical results, traced to additional mutations at codons 168 and 170. This has raised the prospect that other complex NSP samples, particularly imbalanced types (i.e. with the allelic composition X/X/Y) might be artefacts. We will analyse samples classified as complex to confirm whether additional novel polymorphisms might account for these results.

New polymorphisms can interfere with genotyping methods and the information from this work will enhance the accuracy of NSP genotyping. The results will be used for improvements of PrP genotyping technologies to benefit the NSP and other sheep genotyping projects. New haplotypes will provide new insights into the variability of the ovinePrP gene, which is expected to lead to better understanding of the association between PrP genetics and scrapie disease. In the short term, if the sequencing of any sample reveals a convincing technical artefact that appears to preclude the delivery of a genotype from an otherwise conventional 136, 154, 171 genotype, the NSP may be able to certify this animal.
Project Documents
• Executive Summary : Ovine PrP gene sequences from sheep with complex genotypes   (31k)
Time-Scale and Cost
From: 2005

To: 2006

Cost: £29,280
Contractor / Funded Organisations
Institute for Animal Health (BBSRC)
Keywords
Animal Health              
Epidemiology              
Plants and Animals              
Sheep              
TSE              
TSEs              
Fields of Study
Animal Health