Tumour
necrosis factor alpha (
TNF-alpha) is a pro-inflammatory
cytokine that plays a crucial role in the regulation of inflammatory and immune responses. In all vertebrate species the genes encoding
TNF-alpha are located within the major histocompatability complex. In the horse
TNF-alpha has been ascribed a role in a variety of important disease processes. Previously two single nucleotide polymorphisms (SNPs) have been reported within the 5' un-translated region of the equine
TNF-alpha gene. We have examined the equine
TNF-alpha promoter region further for additional SNPs by analysing
DNA from 131 horses (Equus caballus), 19 donkeys (E. asinus), 2 Grant's zebras (E. burchellii boehmi) and one onager (E. hemionus). Two further SNPs were identified at
nucleotide positions 24 (T/G) and 452 (T/C) relative to the first
nucleotide of the 522 bp polymerase chain reaction product. A sequence variant at position 51 was observed between equidae. SNaPSHOT genotyping assays for these and the two previously reported SNPs were performed on 457 horses comprising seven different breeds and 23 donkeys to determine the gene frequencies. SNP frequencies varied considerably between different horse breeds and also between the equine species. In total, nine different
TNF-alpha promoter SNP haplotypes and their frequencies were established amongst the various equidae examined, with some haplotypes being found only in horses and others only in donkeys or zebras. The haplotype frequencies observed varied greatly between different horse breeds. Such haplotypes may relate to levels of
TNF-alpha production and
disease susceptibility and further investigation is required to identify associations between particular haplotypes and altered risk of disease.