Genome-Wide Association Study of Insect Bite Hypersensitivity in Swedish-Born Icelandic Horses

Abstract

Insect bite hypersensitivity (IBH) is the most common allergic skin disease in horses and is caused by biting midges, mainly of the genus Culicoides. The disease predominantly comprises a type I hypersensitivity reaction, causing severe itching and discomfort that reduce the welfare and commercial value of the horse. It is a multifactorial disorder influenced by both genetic and environmental factors, with heritability ranging from 0.16 to 0.27 in various horse breeds. The worldwide prevalence in different horse breeds ranges from 3% to 60%; it is more than 50% in Icelandic horses exported to the European continent and approximately 8% in Swedish-born Icelandic horses. To minimize the influence of environmental effects, we analyzed Swedish-born Icelandic horses to identify genomic regions that regulate susceptibility to IBH. We performed a genome-wide association (GWA) study on 104 affected and 105 unaffected Icelandic horses genotyped using Illumina® EquineSNP50 Genotyping BeadChip. Quality control and population stratification analyses were performed with the GenABEL package in R (λ = 0.81). The association analysis was performed using the Bayesian variable selection method, Bayes C, implemented in GenSel software. The highest percentage of genetic variance was explained by the windows on X chromosomes (0.51% and 0.36% by 73 and 74 mb), 17 (0.34% by 77 mb), and 18 (0.34% by 26 mb). Overlapping regions with previous GWA studies were observed on chromosomes 7, 9, and 17. The windows identified in our study on chromosomes 7, 10, and 17 harbored immune system genes and are priorities for further investigation.

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

“…To increase data size and statistical power in the present study, we combined Icelandic horse data from the Netherlands and Sweden that were previously used in separate studies (Schurink et al, ; Shrestha et al, ). Icelandic horses are regularly exported from Iceland to both the Netherlands and Sweden, and the horses belong to the same international studbook (Lorange, ).…”

“…The present GWA study comprised data on 355 Icelandic horses from Sweden and the Netherlands from previous studies within country (Schurink et al, ; Shrestha et al, ). Previously published IBH data on 280 Exmoor ponies in the UK (Velie et al, ) were used for validation of the markers explaining the largest percentage of genetic variance.…”

“…Data on IBH symptoms were in all three countries gathered using similar questionnaires. In Sweden, the questionnaires were sent to Icelandic horse owners in 2005, and veterinarians later collected blood samples and confirmed the IBH symptoms (Eriksson et al, ; Shrestha et al, ). In the Netherlands, the questionnaire was filled out in 2010 by a researcher interviewing the owners, while a veterinarian examined the horse and collected blood samples (Schurink et al, ).…”

“…The 209 Icelandic horses sampled in Sweden were genotyped on the Illumina EquineSNP50 Genotyping BeadChip containing 54,602 single nucleotide polymorphisms (SNPs) (Shrestha et al, ). The 146 Icelandic horses sampled in the Netherlands were genotyped on the Illumina EquineSNP70 Genotyping BeadChip containing 65,157 SNPs (Schurink et al, ).…”

“…The aim of the present study was to find genomic regions associated with equine IBH susceptibility. To increase the statistical power of the GWA study, we combined data from previously published IBH studies on Icelandic horses in the Netherlands (Schurink et al, ) and Sweden (Shrestha et al, ). To validate non‐randomly associated SNPs identified in this study, Exmoor ponies with known IBH status were genotyped for the markers explaining the largest percentage of genetic variance.…”