The Genetics of scrapie in sarda sheep

Scrapie is a fatal neurodegenerative disease of sheep, goats and muflon belonging to the Transmissible Spongiform Encephalopathies group. It is commonly believed that only three polymorphic codons, namely 136, 154 and 171, of the PRNP gene are of fundamental importance in moderating resistance/susceptibility to scrapie. The PRNP gene can contain many other polymorphic codons, however their association with scrapie is little known. The aim of the study was to estimate the frequencies of the different polymorphisms of the PRNP gene in Sarda breed sheep and their association with scrapie occurrence by using experimental and natural scrapie cases. This study suggests that, in Sarda breed sheep, scrapie occurrence is strongly associated with ARQ/ARQwildtype genotype and that presence of additional dimorphisms beyond those at the codon 136, 154 and 171 results in a comprehensive lower risk of scrapie. In particular, the dimorphisms N176K and M137T are associated with the lowest risk of scrapie, while those L141F and A136V may be associated with a longer incubation period.