Scrapie resistance

Scrapie is a degenerative disease of the central nervous system. The disease is highly contagious and leads inevitable to death. Infection can occur by contaminated water or feed. In addition, scrapie is transmissible within the flock and between certain species for instance by ingesting amniotic fluid or by scavenging on the afterbirth. Contaminated pasture and barns remain contagious for a long time. There is neither a treatment nor a cure. However, it is possible to breed animals with an increased resistance to getting the disease. Scrapie is transmitted by misfolded forms of an intrinsic protein called prion. The prion form that is most, but not completely, resistant to misfolding is ARR. A relatively simple and quick way to learn about which prion form is present in any given animal is to analyze its prion protein gene. The test results from the three gene codons 136, 154 and 171 will be transcribed to the corresponding three amino acid letter code such as ARR. Because of the dual nature of the genome that is represented by a maternal and a paternal genome copy, the code is written twofold such as ARR/ARR. The fifteen most common forms of the prion protein in sheep have been categorized into five classes according to their relative resistance respective susceptibility to scrapie:

 In addition to three codon genotyping, we are able to test a fourth codon, 141, which is associated with the atypical form of scrapie.