Prion protein gene polymorphisms in sheep with natural scrapie and healthycontrols in Norway

Two-hundred and forty healthy sheep and 32 cases of natural scrapie in Norw ay were analysed for disease-linked polymorphisms in the prion protein (PrP ) gene. Scrapie was strongly associated with the presence of a valine polym orphism at codon 136 (V-136), as 68.8% of the cases were homozygous (VV136) and 15.6% were valine/alanine heterozygous (VA(136)). All cases were homoz ygous arginine/arginine at codon 154 (RR154), except two which were homozyg ous histidine/histidine (HH154). All cases except two were homozygous gluta mine/glutamine at codon 171 (QQ(171)), the two exceptions being heterozygou s glutamine/arginine (QR(171)). More than 80% of all scrapie cases in Norwa y have occurred in a Cheviot-related crossbred type of sheep called Rygja. This type of sheep, which is largely restricted to the south-western coast, carries the V-136 allele at a higher frequency than do other breeds of Nor wegian sheep. Polymorphisms at codons 138 and 151 are also described.