Atypical Equine Thrombasthenia (AET)Quick Summary
Phenotype: Horses with platelet dysfunction typically exhibit prolonged and recurrent bleeding. Most commonly, affected horses have intermittent epistaxis (nosebleeds) that are unrelated to exercise.
Mode of Inheritance: Autosomal recessive
Alleles: N = Normal, AET = SEL1L variant
Breeds appropriate for testing: Thoroughbred
Explanation of results:
• Horses with N/N genotype will not have this inherited form of atypical platelet dysfunction (atypical thrombasthenia) and cannot transmit this allele to their offspring.
• Horses with N/AET genotype are not expected to be affected by this inherited form of atypical equine thrombasthenia (AET) but are carriers. They may transmit this AET allele to 50% of their offspring. Matings between two carriers are predicted to produce 25% of affected foals.
• Horses with AET/AET genotypes will likely develop atypical equine thrombasthenia (AET) and will transmit this AET allele to all of their offspring.
Atypical Equine Thrombasthenia (AET) is a heritable autosomal recessive bleeding disorder that affects platelet function in Thoroughbred horses. Platelets consist of cell fragments in the blood that help stop bleeding. This test detects the presence of a genetic variant that has been associated with atypical platelet dysfunction and consequent bleeding disorder in Thoroughbred horses.
The condition is characterized by recurring nosebleeds and prolonged bleeding after injury. Horses with AET typically have abnormal clotting because their platelets are unable to properly bind fibrinogen.
A missense mutation (c.1810A>G) in exon 18 of the suppressor/enhancer of lin-12-like (SEL1L) gene is responsible for AET in Thoroughbred horses and reported by the VGL as the AET allele. This change results in the substitution of the expected amino acid isoleucine by the amino acid valine (p.Ile604Val), which causes a reduced expression of the SEL1L protein in the platelets of affected horses.
At this time, AET has only been identified in Thoroughbred horses. The frequency of the mutation in the population is not yet known but is expected to be low.
Testing recommendations: Testing for this heritable platelet disorder can assist owners and breeders in identifying affected and carrier horses. Horses with one copy of the AET allele are expected to be healthy but are carriers. Every offspring they produce will have a 50% chance of inheriting the affected allele. Matings between two carriers have a 25% chance of producing an affected offspring.