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Breeds: Connemara Pony, Mixed Breed, Unspecified
Description
Hoof Wall Separation Disease (HWSD) is an inherited disorder identified in Connemara ponies and horses crossed with Connemara ponies. It causes the dorsal hoof wall to separate, break, and crack easily, while the coronary band appears normal. All four hooves are affected. Signs typically appear within the first year of life and have been seen in foals as young as 2 to 3 weeks of age.
HWSD is caused by a single-base insertion (c.504_505insC) in the SERPINB11 gene that creates a frameshift and a premature stop codon. Affected ponies show significantly reduced SERPINB11 expression in the hoof, suggesting the gene plays a role in maintaining hoof wall structure. This was the first genetic variant associated with a hoof wall-specific disease in any species.
There is no cure for HWSD. Without an intact hoof wall, affected ponies cannot support their weight effectively, and the resulting chronic inflammation often leads to infection, lameness, and laminitis. A small number of affected ponies develop a milder form that can be managed, but most are eventually euthanized because of pain and progressive damage.
HWSD is inherited as an autosomal recessive trait, so a foal must inherit one copy of the variant from each parent to be affected. Carriers show no signs of the disease, and carrier frequency in the Connemara breed has been estimated at about 15%. DNA screening of breeding stock is the only way to identify carriers and avoid pairings (N/HD x N/HD) that carry a 25% risk of producing an affected foal.
Possible results
| Genotype | Description |
|---|---|
| HD/HD | Affected: Horse has two copies of the HWSD variant and is expected to develop signs of the disorder. All offspring will inherit the variant. |
| N/HD | Carrier: Horse has one copy of the HWSD variant and is not expected to show signs of the disorder. Each offspring has a 50% chance of inheriting the variant. |
| N/N | Clear: Horse does not carry the HWSD variant and cannot pass it on to offspring. |
Breeds Affected
Connemara Pony, Connemara Cross
Reference
SERPINB11 frameshift variant associated with novel hoof specific phenotype in Connemara ponies.
[PMID: 25875171]