Haplotype blocks and heterozygosity rich regions on ECA2 in Swedish Warmblood horses

The Fragile Foal Syndrome (FFS) is a disease caused by a recessive lethal missense mutation in the PLOD1 gene (ECA2). Despite its harmful effect, a relatively high frequency of the FFS allele carriers has been found in the Swedish Warmblood (SWB), suggesting a heterozygous advantage. Balancing selection can be further studied in haplotype blocks and increased heterozygosity around the target of selection. In this study we evaluated the presence of haplotype blocks and Runs of Heterozygosity on ECA2 in 380 SWB horses divided by sport discipline. In horses mainly bred for dressage a haplotype block comprising the FFS variant was found. On average 11.7 Runs of Heterozygosity were identified per horse on ECA2, with no significant difference in numbers between the sport disciplines. This study provides a preliminary characterization of haplotype blocks and heterozygosity rich regions on ECA2 which may further corroborate the potential presence of balancing selection for the FFS allele.