title: The same ELA class II risk factors confer equine insect bite hypersensitivity in two distinct populations.
abstract: Insect bite hypersensitivity (IBH) is a chronic allergic dermatitis common in horses. Affected horses mainly react against antigens present in the saliva from the biting midges, Culicoides ssp, and occasionally black flies, Simulium ssp. Because of this insect dependency, the disease is clearly seasonal and prevalence varies between geographical locations. For two distinct horse breeds, we genotyped four microsatellite markers positioned within the MHC class II region and sequenced the highly polymorphic exons two from DRA and DRB3, respectively. Initially, 94 IBH-affected and 93 unaffected Swedish born Icelandic horses were tested for genetic association. These horses had previously been genotyped on the Illumina Equine SNP50 BeadChip, which made it possible to ensure that our study did not suffer from the effects of stratification. The second population consisted of 106 unaffected and 80 IBH-affected Exmoor ponies. We show that variants in the MHC class II region are associated with disease susceptibility (p (raw) = 2.34 × 10(-5)), with the same allele (COR112:274) associated in two separate populations. In addition, we combined microsatellite and sequencing data in order to investigate the pattern of homozygosity and show that homozygosity across the entire MHC class II region is associated with a higher risk of developing IBH (p = 0.0013). To our knowledge this is the first time in any atopic dermatitis suffering species, including man, where the same risk allele has been identified in two distinct populations.
authors.affiliation: Department of Animal Breeding and Genetics, Swedish University of Agricultural Sciences, Box 597, SE-751 24, Uppsala, Sweden.
authors.forename: Lisa S
authors.initials: LS
authors.lastname: Andersson
authors.forename: June E
authors.initials: JE
authors.lastname: Swinburne
authors.forename: Jennifer R S
authors.initials: JR
authors.lastname: Meadows
authors.forename: Hans
authors.initials: H
authors.lastname: Broström
authors.forename: Susanne
authors.initials: S
authors.lastname: Eriksson
authors.forename: W Freddy
authors.initials: WF
authors.lastname: Fikse
authors.forename: Rebecka
authors.initials: R
authors.lastname: Frey
authors.forename: Marie
authors.initials: M
authors.lastname: Sundquist
authors.forename: Chia T
authors.initials: CT
authors.lastname: Tseng
authors.forename: Sofia
authors.initials: S
authors.lastname: Mikko
authors.forename: Gabriella
authors.initials: G
authors.lastname: Lindgren
mesh_terms: D000818:Animals; D002519:Ceratopogonidae / Q000276:immunology*; D003876:Dermatitis, Atopic / Q000235:genetics / Q000276:immunology / Q000662:veterinary*; D005802:Genes, MHC Class II; D005838:Genotype; D006734:Horse Diseases / Q000235:genetics* / Q000276:immunology; D006736:Horses; D007299:Insect Bites and Stings / Q000235:genetics / Q000276:immunology / Q000662:veterinary*; D018895:Microsatellite Repeats; D020641:Polymorphism, Single Nucleotide; D012307:Risk Factors