Abstract
BackgroundInsect bite hypersensitivity is a common allergic disease in horse populations worldwide. Insect bite hypersensitivity is affected by both environmental and genetic factors. However, little is known about genes contributing to the genetic variance associated with insect bite hypersensitivity. Therefore, the aim of our study was to identify and quantify genomic associations with insect bite hypersensitivity in Shetland pony mares and Icelandic horses in the Netherlands.MethodsData on 200 Shetland pony mares and 146 Icelandic horses were collected according to a matched case–control design. Cases and controls were matched on various factors (e.g. region, sire) to minimize effects of population stratification. Breed-specific genome-wide association studies were performed using 70 k single nucleotide polymorphisms genotypes. Bayesian variable selection method Bayes-C with a threshold model implemented in GenSel software was applied. A 1 Mb non-overlapping window approach that accumulated contributions of adjacent single nucleotide polymorphisms was used to identify associated genomic regions.ResultsThe percentage of variance explained by all single nucleotide polymorphisms was 13% in Shetland pony mares and 28% in Icelandic horses. The 20 non-overlapping windows explaining the largest percentages of genetic variance were found on nine chromosomes in Shetland pony mares and on 14 chromosomes in Icelandic horses. Overlap in identified associated genomic regions between breeds would suggest interesting candidate regions to follow-up on. Such regions common to both breeds (within 15 Mb) were found on chromosomes 3, 7, 11, 20 and 23. Positional candidate genes within 2 Mb from the associated windows were identified on chromosome 20 in both breeds. Candidate genes are within the equine lymphocyte antigen class II region, which evokes an immune response by recognizing many foreign molecules.ConclusionsThe genome-wide association study identified several genomic regions associated with insect bite hypersensitivity in Shetland pony mares and Icelandic horses. On chromosome 20, associated genomic regions in both breeds were within 2 Mb from the equine lymphocyte antigen class II region. Increased knowledge on insect bite hypersensitivity associated genes will contribute to our understanding of its biology, enabling more efficient selection, therapy and prevention to decrease insect bite hypersensitivity prevalence.
Highlights
Insect bite hypersensitivity is a common allergic disease in horse populations worldwide
In Shetland pony mares, confounding of Insect bite hypersensitivity (IBH) with relevant effects such as region and withers height category was negligible, since the analysis revealed no significant association between IBH and these effects
The genome-wide association study performed here identified several genomic regions associated with IBH in both Shetland pony mares and Icelandic horses
Summary
Insect bite hypersensitivity is a common allergic disease in horse populations worldwide. Insect bite hypersensitivity is affected by both environmental and genetic factors. Little is known about genes contributing to the genetic variance associated with insect bite hypersensitivity. Insect bite hypersensitivity (IBH) is a common allergic skin disease in various horse breeds found throughout the world, and results from bites of Culicoides spp. Sensitive horses develop a severe itch, which results in selfinflicted trauma and severely affected horses sometimes need to be euthanized [1]. Methods to prevent or reduce clinical symptoms often require dedication from the owner and greatly differ in efficiency e.g. Owners of affected horses incur costs related to preventive or curative methods and veterinary consultation. The commercial value of affected horses is reduced and use of affected horses can be restricted due to discomfort and disfiguration [1]
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