Submitted to: American Society of Animal Science
Publication Type: Proceedings
Publication Acceptance Date: 4/10/2005
Publication Date: 6/22/2005
Citation: Johnson, M.L., Evoniuk, J.M., Stoltenow, C.L., Orourke, K.I., Redmer, D.A. 2005. Development of an assay to determine single nucleotide polymorphisms (snp) in the prion gene for the diagnosis of genetic susceptibility to scrapie in sheep. American Society of Animal Science. 56:151.
Interpretive Summary: Susceptibility to scrapie, a fatal prion disease of sheep, is controlled by a two changes in the DNA sequence in the host gene for the normal prion protein. Sheep with the 171QR or 171RR genotypes are generally protected from disease and sheep with the 136VV or 136AV genotype are highly susceptible to some forms of scrapie. Sheep with the protective genotypes are often selected as breeding stock. The objective of this study was to develop a reliable assay to genotype sheep for scrapie susceptibility. An assay using DNA from blood or muscle was developed and evaluated. Test accuracy was greater than 99%. This test is accurate, relatively easy to perform, and will be a useful tool for research projects investigating the mechanisms of protection from scrapie.
Technical Abstract: Scrapie is a transmissible spongiform encephalopathy of sheep. Although scrapie is transmitted under field conditions, susceptibility is limited to sheep of a few PRNP genotypes. Sheep homozygous for the allele encoding alanine at codon 136 (136A) and glutamine at 171 (171Q) are susceptible the most common US scrapie strain. Sheep heterozygous or homozygous for an alternative allele encoding arginine at 171 (171R) are rarely infected. When exposed to the minor US strain, sheep homozygous or heterozygous for the allele encoding valine at codon 136 (V136) are susceptible; presence of the 171R allele delays onset of clinical signs but does not confer resistance. The objective of this study was to develop a relatively simple, accurate genotyping test to identify susceptible sheep. A real time polymerase chain reaction assay to detect the single nucleotide polymorphisms at codons 136 and 171 was developed. In a pilot sample of 70 samples, the error rate was less than 1%. SNP genotyping was relatively easy to perform, inexpensive, and suitable for large scale testing of flocks. The assay will be useful in research projects investigating the mechanism of scrapie resistance.