Glanzmann thrombasthenia in a 17-year-old Peruvian Paso mare

A 17-year-old Peruvian Paso mare was evaluated for bilateral epistaxis that had been present for at least 3 years. The mare had mild ane- mia, platelet count within the reference interval, unremarkable coagula- tion times, and a negative Coggins test. On endoscopic examination, structural abnormalities were not observed in the nasal cavities, pharynx, larynx, trachea, or either guttural pouch, but petechiation was noted in the nasal mucosa. Additional tests revealed prolonged cutaneous bleeding time, normal concentration of von Willebrand factor antigen, an abnormal clot retraction test, and failure of plalelet aggregation in response to ago- nists, suggesting a functional disorder of platelets. Genetic analysis indi- cated the horse was homozygous for a 10-base-pair deletion that included the last 3 base pairs of exon 11 and the first 7 base pairs of intron 11 of the gene encoding glycoprotein IIb. The diagnosis was Glanzmann thrombas- thenia (GT) caused by a structural defect in glycoprotein IIb. GT is an au- tosomal recessive disorder caused by a defect in the glycoprotein IIb-IIIa complex on platelet surfaces. Separate genes encode each glycoprotein, and mutations in either gene can result in GT. This case of GT is unique given the age of the mare at the time of diagnosis. We conclude that GT, although an inherited disorder, should be considered in horses with sus- pected dysfunctional platelets, regardless of age.