Submitted to: Plant and Animal Genome Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 1/10/2004
Publication Date: 1/10/2004
Citation: HEATON, M.P., LEYMASTER, K.A., FREKING, B.A., LAEGREID, W.W. ACCURATE DETERMINATION OF PRNP HAPLOTYPES IN U.S. SHEEP. PLANT AND ANIMAL GENOME CONFERENCE PROCEEDINGS. 2004. ABSTRACT NO. P312.
Technical Abstract: Scrapie is a fatal, transmissible disease affecting the central nervous system of sheep. Scrapie eradication is a national priority of the U.S. sheep industry. Variation in the prion gene (PRNP) sequence has been correlated with differences in scrapie susceptibility. A PRNP haplotype allele encoding alanine, arginine, and arginine (ARR) at positions 136, 154, and 171, respectively, is correlated with increased resistance; whereas a haplotype encoding valine, arginine, and glutamine (VRQ) at those positions is correlated with increased susceptibility. Haplotype alleles encoding four other known forms of the protein (ARQ, AHQ, ARH, ARK) have intermediate or unknown correlations with scrapie susceptibility. Although accurate determination of PRNP haplotypes is important, it is not trivial. Five single nucleotide polymorphisms (SNPs) determine which amino acids are encoded at positions 136, 154, and 171. Moreover, a 400-bp region encompassing these codons contains 15 additional SNPs that may interfere with genotype assays. Here we describe a polymerase chain reaction assay that consistently amplifies both alleles of the PRNP locus. We also describe a means for accurately determining an animal's PRNP haplotypes by either DNA sequencing or mass spectrometry. Assays were verified in the MARC Sheep Diversity Panel (version 1.1) and used to estimate PRNP haplotype frequencies in two MARC composite flocks fixed for alternative callipyge alleles. In the 421 ewes, frequencies of ARR, ARQ, and VRQ haplotypes were 0.325, 0.601, and 0.074, respectively. Selection to increase the frequency of the favorable haplotype (ARR) is being practiced in each flock.