Evolutionary history of DLA class II haplotypes in canine diabetes mellitus through single nucleotide polymorphism genotyping

Strong linkage disequilibrium (LD) is a characteristic of the major histocompatibility complex (MHC) region, as well as the genome in general in dogs as a consequence of demographic changes with domestication. Disease association studies of MHC haplotypes may be affected by high LD and the resultant shared genetic backgrounds of haplotypes giving associations with linked but non-causative mutations, and also by convergent haplotypes, in which combinations of alleles have arisen independently. This study provides preliminary tools for dog leukocyte antigen (DLA) class II haplotype analysis with 102 single nucleotide polymorphisms (SNPs) identified in 14.6 kb and genotyping of 20 of these SNPs to tag haplotypes in 60 dogs with diabetes mellitus and in 49 non-diabetic dogs. The pattern of LD and analysis of SNP patterns indicated combinations of exon 2 alleles have arisen through both recombination and convergence. For exon 2 haplotypes associated with susceptibility or protection from diabetes mellitus, a region of fixed differences in SNPs across the DQ region was observed, suggesting a region outside exon 2 may be implicated in disease association. Four new DQB1 promoter alleles restricted to diabetic dogs were identified, as well as a substitution difference in the X1 box of the DQB1 promoter that will potentially modify the effect of the protective haplotypes within diabetic dogs.