University of California–Davis researchers recently discovered the genetic mutation that causes a rare hoof disorder in Connemara ponies.

In hoof wall separation disease (HWSD), the hoof wall splits along its weight-bearing surface. HWSD is often confused with laminitis or white line disease, but it differs from those conditions in that the separation occurs within the hoof wall, rather than between the wall and coffin bone.

Noting that horses with HWSD usually have two normal parents and begin showing signs by the time they are a year old, the California researchers suspected that the condition was autosomal recessive, which means it is expressed only in individuals who carry two copies of a mutated gene. In such disorders, unaffected “carrier” horses have only one copy of the faulty gene. If two carrier horses are bred and both happen to pass along a copy of the mutated gene, the resulting foal develops the condition.

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Researchers at the Bannasch Laboratory, which is part of the UC–Davis School of Veterinary Medicine, used an approach called genome-wide association analysis to first identify the chromosome where the defective gene was located.

Through whole genome sequencing, they identified a mutation in the gene that produces a protein called SERPINB11. In a study population of more than 300 Connemara ponies, 23 were found to have double copies of the faulty gene and all showed signs of HWSD. None of the control horses, who had normal hooves, carried two copies of the gene.

The researchers also determined that approximately one in seven unaffected ponies carried one copy of the mutated gene. Noting that the role SERPINB11 plays in the production and maintenance of normal hoof wall tissue is still unclear, they call for further investigation.

Reference: “SERPINB11 frameshift variant associated with novel hoof specific phenotype in Connemara ponies,” PLOS Genetics, April 2015

This article first appeared in EQUUS issue #457

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