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, GTe2 = ITGA2B exon 2 variant, GTe11 = ITGA2B exon 11 variant
Breeds appropriate for testing: Peruvian Paso, Oldenburg, Quarter Horse, Thoroughbred
Explanation of results:
• Horses with N/N genotype will not have this inherited form of platelet dysfunction (thrombasthenia) and cannot transmit these alleles to their offspring.
• Horses with N/GTe2 genotype are not expected to be affected by this inherited form of Glanzmann thrombasthenia (GT) but are carriers. They may transmit this GTe2 allele to 50% of their offspring. Matings between two carriers are predicted to produce 25% of affected foals.
• Horses with N/GTe11 genotype are not expected to be affected by this inherited form of Glanzmann thrombasthenia (GT) but are carriers. They may transmit this GTe11 allele to 50% of their offspring. Matings between two carriers are predicted to produce 25% of affected foals.
• Horses with GTe2/ GTe2 genotype will likely develop Glanzmann thrombasthenia (GT) and will transmit this GTe2 allele to all their offspring.
• Horses with GTe11/GTe11 genotypes will likely develop Glanzmann thrombasthenia (GT) and will transmit this GTe11 allele to all their offspring.
• Horses with GTe2/GTe11 genotype will likely develop Glanzmann thrombasthenia (GT) and will transmit either a GTe2 or GTe11 allele to all their offspring.
Glanzmann thrombasthenia (GT) is a heritable autosomal recessive bleeding disorder that affects platelet function in horses. Platelets consist of cell fragments in the blood that help stop bleeding. This test detects the presence of two genetic variants that have been associated with GT, leading to platelet dysfunction and a consequent bleeding disorder in the horse.
The condition is characterized by recurrent episodes of epistaxis (nosebleed). Horses with GT may have coagulation panel results within the normal ranges, although clot retraction is often abnormal and platelet aggregation reduced.
Two variants in the integrins alpha-2B (ITGA2B) gene are responsible for GT in horses: a missense variant in exon 2 (c.215G>C) that causes a substitution of the expected amino acid Arginine by a Proline (R72P), reported by the VGL as the GTe2 allele; and a 10-base pair deletion spanning the junction between exon 11 and the subsequent intron (EquCab3.0 chr11:19,247,983–19,247,992delCAGGTGAGGA), reported by the VGL as the GTe11 allele.
The frequency of the GTe2 and GTe11 mutations in the affected breeds 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 any of the alleles (GTe2 or GTe1) 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.