Hoof Wall Separation Syndrome (HWSS)

Gene: SERPINB11

Transmission: Autosomal recessive

For an autosomal recessive genetic disease an animal must have two copies of the mutation in question to be at risk of developing the disease. Both parents of an affected animal must be carriers of at least one copy of the mutation. Animals that have only one copy of the mutation are not at risk of developing the disease but are carrier animals that can pass the mutation on to future generations.

Mutation: Insertion, SERPINB11 gene; c.504_505 ins C, p.(T169H fs STOP 3), chr.8.

Medical system: Dermal

Breeds: Connemara Pony

Age of onset of symptoms: Within the first 6 months of life.

Hoof Wall Separation Syndrome (HWSS) is a hereditary disease of Connemara ponies, a pony breed originating from Ireland. HWSS involves insufficient development of keratin in the outer hoof wall, which normally gives the hoof its strength and hardness. As early as the first 6 months of life, breaks and cracks can be observed in the outer hoof wall. Generally, all four hooves are affected, but the coronary band, sole and white line appear healthy. An affected horse bears its weight on the sole of the hoof (where a proliferative horn may develop) rather than on the wall. This can lead to chronic inflammation, severe lameness and/or laminitis. While some cases are mild, others are more severe, and euthanasia may be necessary if the horse’s quality of life is compromised. Molecular studies identified a mutation within the SERPINB11 gene as being responsible for the disease phenotype when in the homozygous state. In a survey study of 324 animals not related to disease cases, a carrier frequency of 14.8% was observed. The availability of a DNA test will allow breeders of the Connemara Pony to identify carrier animals and to eliminate HWSS and eventually the mutation from their animals via selective breeding.

References:

Lien OMIA : [1897-9796]

Finno CJ. (2022) Hoof wall separation disease: A Review. Equine Vet Educ 34(9):501–502. [pm/36172455]

Finno CJ, Stevens C, Young A, et al. (2015) SERPINB11 frameshift variant associated with novel hoof specific phenotype in Connemara Ponies. PLOS Genet 11(4):e1005122. [pm/25875171]

Contributed by: Éliane Jutras and Alexia Croteau, Class of 2028, Faculty of Veterinary Medicine, University of Montreal. (Translation, DWS)