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Phenotype: Hoof wall separation disease (HWSD) is characterized by a hoof wall that easily breaks and cracks, and a normal-appearing coronary band.
Mode of Inheritance: Autosomal recessive
Alleles: N = Normal/Unaffected, HWSD = Hoof wall separation disease
Breeds appropriate for testing: Connemara Pony
Explanation of Results:
- Horses with N/N genotype will not have hoof wall separation disease and cannot transmit this hoof wall separation disease variant to their offspring.
- Horses with N/HWSD genotype will not be affected by hoof wall separation disease, but are carriers. They may transmit this hoof wall separation disease variant to 50% of their offspring. Matings between two carriers will result in a 25% chance of producing a hoof wall separation disease-affected foal.
- Horses with HWSD/HWSD disease are highly likely to be affected by hoof wall separation disease.
Hoof wall separation disease (HWSD) is a genetic defect characterized by a hoof wall that easily breaks and cracks, and a normal appearing coronary band. The breaks and cracks begin to occur in young ponies. In severe cases the pony bears weight entirely on the sole of the foot which can lead to severe lameness.
HWSD is caused by a frameshift mutation in the gene SERPINB11, (c.504_505insC), and is inherited as an autosomal recessive trait. This means that carriers are completely normal and only animals with two copies of the mutation will show clinical signs of the disease. HWSD appears to occur only in the Connemara Pony and the carrier frequency has been estimated to be about 14.8%. A DNA test for this specific mutation can determine if ponies are normal or if they carry one or two copies of the mutation. Ponies that carry two copies of the mutation are highly likely to be affected with the disease. Some cases are milder while others are more severe. We have identified at least one case where the pony does not appear to have clinical signs associated with having two copies of the mutation. This indicates that the mutation is not fully penetrant; however it has very high penetrance of 96.8%.
Ponies that have only one mutant copy of HWSD (N/HWSD) are normal, but they are carriers of the disease. When two carriers are bred to each other, the resulting foals can be affected. At the time that this test was released, approximately 15% of Connemara were carriers of HWSD (N/HWSD); however, the number of carriers can change with each generation. Ponies that are carriers of HWSD are completely normal, and they can be safely bred to non-carrier, normal ponies (N/N) in order to maintain diversity within the breed and to select for other positive attributes in carriers.
Testing for hoof wall separation disease is important in assisting clinicians, owners, and breeders in identifying affected and carrier horses. Breeders can use results from the test as a tool for selection of mating pairs to avoid producing affected horses.
Type of Test
|Test Result||Connemara Pony Hoof Wall Separation Disease|
|N/N||No copies of HWSD mutation. Animal is normal.|
1 copy of HWSD mutation. Animal is normal but is a carrier.
2 copies of HWSD mutation. Animal is affected.
Finno, C. J., Stevens, C., Young, A., Affolter, V., Joshi, N. A., Ramsay, S., & Bannasch, D. L. (2015). SERPINB11 Frameshift Variant Associated with Novel Hoof Specific Phenotype in Connemara Ponies. PLOS Genetics, 11(4). doi: 10.1371/journal.pgen.1005122