Glanzmann thrombasthenia in an Oldenbourg filly.

This study presents the case of an 18-month-old Oldenbourg filly diagnosed with Glanzmann thrombasthenia, a rare bleeding disorder. The diagnosis was based on several abnormal laboratory findings such as prolonged bleeding time, absence of clot retraction, reduced platelet aggregation, and decreased expression of certain antigens on the horse’s platelets.

Research Context and Methodology

• This research aims to identify the cause of a bleeding diathesis in an 18-month-old Oldenbourg filly. Bleeding diathesis is a term used to describe an unusual susceptibility to bleeding, typically due to abnormalities in the body’s clotting processes.
• The evaluation involved various laboratory tests. The tests included platelet count, gingival bleeding time, prothrombin time (PT), activated partial thromboplastin time (aPTT), von Willebrand factor (vWf) antigen test, clottable fibrinogen, clot retraction time, PFA-100 closure time, platelet aggregometry (on platelet-rich plasma), and thrombelastography.
• Thrombelastography (TEG) was used to determine the efficiency of the fibrin clot formation process, and the clot’s resistance to breakdown. This was achieved by using kaolin and tissue factor as coagulation activators.
• The fibrinogen receptor on the filly’s platelets was examined using flow cytometry with specific antibodies.

Laboratory Findings and Diagnosis

• In this study, abnormal laboratory findings were observed. These abnormal results included a heightened oral mucosal bleeding time of over 12 hours, a prolonged closure time with collagen/ADP of over 300 seconds, and an absence of clot retraction after 60 minutes.
• Through thrombelastography, it was found that there was no significant difference in the reaction times with kaolin and tissue factor when the patient and a control horse were compared. However, in the patient filly, the maximum amplitudes were reduced with both kaolin and tissue factor.
• With regard to platelet aggregation, responses to ADP and collagen were significantly reduced in the affected horse compared with the control.
• Flow cytometry revealed an absence of CD41 and decreased expression of CD41/CD61-reacting antigen on the filly’s platelets, unlike the control horse.
• The collective laboratory findings indicated a diagnosis of Glanzmann thrombasthenia, a rare inherited disorder characterized by impaired clot formation due to a defect or deficiency in glycoprotein IIb/IIIa (GPIIb/IIIa), platelet surface protein complex required for platelet aggregation. The cause of this condition is likely a mutation in the gene encoding the GPIIb subunit.