Large-scale PRNP genotyping of small ruminants using an automated high-throughput MALDI-TOF MS assay

Scrapie resistance or susceptibility in sheep is associated with single nucleotide polymorphisms (SNPs) at codons 136, 154, and 171 of the prion protein gene (PRNP). In addition, phenylalanine mutation at codon 141 has been recognized as a risk factor for atypical scrapie. In contrast, K222, D146, and S146 alleles confer genetic resistance to classical scrapie in goats. High-throughput genotyping technologies would provide significant benefits in scrapie eradication plans. The ability to resolve oligonucleotides varying in mass by less than a single nucleotide makes MALDI-TOF mass spectrometry (MS) a suitable platform for PRNP genotyping. We evaluated the commercial Myriapod scrapie kit (Diatech Pharmacogenetics), associated with a highly automated processing platform incorporating MALDI-TOF MS technology, to detect SNPs at codons 136, 154, 171, 141, and 222 of small ruminant PRNP. The Myriapod scrapie kit was accredited according to UNI CEI EN ISO/IEC 17025. We present the genotyping results of 10,960 sheep in Sicily and 1,822 goats in Sicily and Calabria (southern Italy) tested during 2017. We found a high frequency (43.9%) of the protective ARR allele in sheep and a promising 12.3% of the resistant K222 variant in goats. This efficient and high-throughput method is suitable for extensive PRNP genotyping, as requested in the European scrapie eradication plan.