Prion protein gene polymorphisms in sheep with natural scrapie and healthy controls in Norway

Two-hundred and forty healthy sheep and 32 cases of natural scrapie in Norway were analysed for disease-linked polymorphisms in the prion protein (PrP) gene. Scrapie was strongly associated with the presence of a valine polymorphism at codon 136 (V136), as 68.8% of the cases were homozygous (VV136) and 15.6% were valine/alanine heterozygous (VA136). All cases were homozygous arginine/arginine at codon 154 (RR154), except two which were homozygous histidine/histidine (HH154). All cases except two were homozygous glutamine/glutamine at codon 171 (QQ171), the two exceptions being heterozygous glutamine/arginine (QR171). More than 80% of all scrapie cases in Norway 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 V136 allele at a higher frequency than do other breeds of Norwegian sheep. Polymorphisms at codons 138 and 151 are also described.