There are certain residues in the sheep prion protein that have been associated with the infectivity of classical scrapie. These are residues 136, 154 and 171, and researches have shown that PRNP genotypes for the corresponding codons have different susceptibilities to classical scrapie. Ranging from the most risk to the least, the genotypes (residues 136, 154 and 171, respectively) are VRQ/VRQ, ARQ/ARQ, AHQ/AHQ and ARR/ARR. In 2003, the European Union introduced a regulation, which declared that the risk allele (VRQ) should be eliminated, while increasing the frequency of the most resistant allele. This regulation was mandatory for the member states from 2005.
Iceland‘s policy towards this regulation, as a non-member state, has been to remove rams from breeding stations, that carry a VRQ allele. Also, although it is not mandatory, farmers can have their rams genotyped. However, the allele ARR has never been identified in Iceland and therefore, it cannot be used for breeding, as is done in other countries in Europe. The effect of Iceland‘s policy has never been analyzed but this project will assess whether there has been a change in the distribution of PRNP genotypes in classical scrapie flocks and in classical scrapie sheep that show symptoms, and whether there has been a change in age of classical scrapie sheep that show symptoms.