Indirect carrier detection of canine haemophilia A using factor VIII microsatellite markers

A panel of factor VIII microsatellite markers was developed for indirect carrier detection of canine haemophilia A (factor VIII deficiency). A total of 78 dogs, representing 14 different breed variants of haemophilia A, were genotyped at six intragenic factor VIII marker loci. The markers spanned approximately 110 kb and were located in the 5' UTR of the factor VIII (F8) gene and within introns 6, 10, 12, 14 and 21. The observed heterozygosity (n = 39 females) for these markers was 0.675, 0.82, 0.868, 0.692, 0.473 and 0.775 respectively. The affected males of each breed variant had unique marker haplotypes. In addition, the marker haplotypes varied for two unrelated haemophilic Jack Russell terriers, compatible with independent mutation events causing haemophilia in different breeds and different families. A three-marker panel (markers within introns 6, 10 and 21) was informative for 37 of the 39 females. The haemophilia-associated haplotype was defined for six breed variants based on the genotypes of an affected male and a clear male sibling, with successful carrier detection of female siblings in each pedigree. Our results demonstrate an apparent allelic heterogeneity in canine haemophilia A; however, an indirect method based on a three-marker panel is feasible to facilitate carrier detection and genetic counselling.