SERPINB11 Associated with Novel Hoof Specific Phenotype in Connemara Ponies

An inherited disease characterized by a phenotype restricted to the dorsal hoof wall was identified in the Connemara pony. Hoof wall separation disease (HWSD) manifests clinically as separation of the dorsal hoof wall along the weight-bearing surface of the hoof during the first year of life. Parents of affected ponies appeared clinically normal, suggesting an autosomal recessive mode of inheritance. A case-control allelic genome wide association analysis was performed (n_cases=15, n_controls=24). A genome-wide significant association was detected on chromosome 8 (p_raw=7.51x10^-11, p_genome=1.92x10^-5). A homozygous region identified in affected ponies spanned 79,846,316-81,698,072 bp and contained a family of 13 annotated SERPINB genes. Whole genome next-generation sequencing at 6x coverage of two cases and two controls revealed 9,758 SNVs and 1,230 in/dels within the 1.8-Mb haplotype, of which 17 and 5, respectively, segregated with the disease and were located within or adjacent to genes. Additional genotyping of these 22 putative functional variants in 369 Connemara ponies (n_cases=23, n_controls=346) and 169 horses of other breeds revealed segregation of three putative variants adjacent or within four SERPIN genes. Evaluation of mRNA levels at the proximal hoof capsule (n_cases=4, n_controls=4) revealed that SERPINB11 expression was significantly reduced in affected ponies (p<0.001). Carrier frequency was estimated at 14.8%. This study describes the first genetic mutation resulting in a hoof wall specific phenotype and suggests a role of SERPINB11 in maintaining hoof wall structure.