Genome-wide association study for insect bite hypersensitivity susceptibility in horses revealed novel associated loci on chromosome 1.

This study focuses on discovering genetic origins for the susceptibility of horses to insect bite hypersensitivity (IBH), a skin allergy caused by biting midges. The researchers have identified and qualified certain genetic variations associated with this vulnerability, providing insights into the genes and regulatory processes involved in these horse breeds’ predisposition to IBH.

Research Background

• The focus of the research was equine insect bite hypersensitivity (IBH), a skin allergy in horses that results from bites by midges, primarily of the Culicoides species. This condition is not only common in certain horse breeds but also poses a financial strain due to increased care and management costs.
• IBH is inherited polygenically, meaning multiple genes contribute to its occurrence. The researchers aimed to pinpoint single nucleotide polymorphisms (SNPs)—variations in individual DNA building blocks—that associate with a susceptibility to this condition.

Methodology

• The team performed a genome-wide association study, examining genetic variants across entire genomes to find genetic associations with a particular trait—in this case, IBH.
• The subjects of the research were 177 Icelandic horses affected by IBH and 178 unaffected ones. After quality control measures, the scientists examined 33,523 SNPs for their correlation with IBH presence.

Results

• The study identified associated regions in equine chromosomes 1, 3, 15, and 18. Some of these overlapped with areas previously known to be linked with IBH in horses, while others were newly associated regions.
• The areas identified by the research team collectively explained about 11.46% of the total genetic variance—variation in a particular trait attributable to genetic factors—in relation to IBH.

Validation and Novel Findings

• For validation, the scientists examined three SNPs; on equine chromosomes 1 and X, which explained the most significant portion of genetic variance, in an independent population of 280 Exmoor ponies.
• A previously associated genomic region on chromosome 1 (at 152-153 mb) was validated in the Exmoor ponies. This region contains the AQR gene, which is involved in the process of splicing—editing out introns, or non-coding sections of pre-messenger RNA, before translation into proteins. It also harbors a long non-coding RNA (a form of RNA that does not code for proteins but often has regulatory functions).

Conclusions

• The results confirm that multiple genes contribute to IBH susceptibility in horses, underlining its polygenic nature.
• The investigation also suggests that the underlying mechanism for IBH predisposition in these horse breeds could involve transcriptional regulatory mechanisms, such as alternative splicing.