Genetic evidence for susceptibility and resistance against scrapie in Indian sheep.

Abstract

Scrapie is a fatal, neurodegenerative disease of sheep and goats (Prusiner 1982). The cause behind the disease is infection by prion proteins (Prusiner 1982). The progression of scrapie is known to be influenced by the amino acid polymorphism of the host prion protein (PRNP) gene (Belt et al. 1995). The present study was carried out on Indian sheep breeds i.e., Karnah, Mandya, Malpura and Garole to identify polymorphisms of the PRNP gene at codons (136, 154 and 171) responsible for the susceptibility and resistance of the scrapie disease in sheep. The known risky allele (ARQ) was found to be the most frequent (77.75%). The most resistant (ARR) and most susceptible (VRQ) alleles were found equally distributed with a frequency of 1.75%. Although, most of the alleles were known to confer susceptibility or partial susceptibility to scrapie, yet so far none of the Indian sheep breeds showed any clinical symptoms of the disease. The possible reason could be genotype–environment interaction, management practices and/or resistance of Indian sheep to scrapie via some other mechanism. Fatal neurodegenerative prion diseases are both genetic and infectious to humans and other mammals (Prusiner 1991). Scrapie is considered as a prototype of various forms of prion diseases that include bovine spongiform encephalopathy (BSE) in cattle and Creutzfeldt–Jakob disease in human (Prusiner 1991). It is characterized by the accumulation of an abnormal isoform of the PRNP in the central nervous system (Prusiner 1991). Scrapie is a rare, contagious, slowly progressive, endemic brain disease in