| Glanzmann's thrombasthenia | |
| Synonyms: | Thrombasthenia of Glanzmann and Naegeli[1] |
Glanzmann's thrombasthenia is an abnormality of the platelets. It is an extremely rare coagulopathy (bleeding disorder due to a blood abnormality), in which the platelets contain defective or low levels of glycoprotein IIb/IIIa (GpIIb/IIIa), which is a receptor for fibrinogen. As a result, no fibrinogen bridging of platelets to other platelets can occur, and the bleeding time is significantly prolonged.
Characteristically, there is increased mucosal bleeding:
The bleeding tendency is variable but may be severe. Bleeding into the joints, particularly spontaneous bleeds, are very rare, in contrast to the hemophilias. Platelet numbers and morphology are normal. Platelet aggregation is normal with ristocetin, but impaired with other agonists such as ADP, thrombin, collagen, or epinephrine.
Glanzmann's thrombasthenia can be inherited in an autosomal recessive manner[2] or acquired as an autoimmune disorder.[2] [3]
The bleeding tendency in Glanzmann's thrombasthenia is variable,[2] some individuals having minimal bruising, while others have frequent, severe, potentially fatal hemorrhages. Moreover, platelet αIIbβ3 levels correlate poorly with hemorrhagic severity, as virtually undetectable αIIbβ3 levels can correlate with negligible bleeding symptoms, and 10%–15% levels can correlate with severe bleeding.[4] Unidentified factors other than the platelet defect itself may have important roles.[2]
Glanzmann's thrombasthenia is associated with abnormal integrin αIIbβ3, formerly known as glycoprotein IIb/IIIa (GpIIb/IIIa),[5] which is an integrin aggregation receptor on platelets. This receptor is activated when the platelet is stimulated by ADP, epinephrine, collagen, or thrombin. GpIIb/IIIa is essential to blood coagulation since the activated receptor has the ability to bind fibrinogen (as well as von Willebrand factor, fibronectin, and vitronectin), which is required for fibrinogen-dependent platelet-platelet interaction (aggregation). Understanding of the role of GpIIb/IIIa in Glanzmann's thrombasthenia led to the development of GpIIb/IIIa inhibitors, a class of powerful antiplatelet agents.[6] [7]
Light transmission aggregometry is widely accepted as the gold standard diagnostic tool for assessing platelet function, and a result of absent aggregation with any agonist except ristocetin is highly specific for Glanzmann's thrombasthenia.[8] Following is a table comparing its result with other platelet aggregation disorders:
Therapy involves both preventive measures and treatment of specific bleeding episodes.[2]
It is named after Eduard Glanzmann (1887–1959), the Swiss pediatrician who originally described it.[10] [11]
The subsequent studies, following Eduard Glanzmann's description of hemorrhagic symptoms and "weak platelets", demonstrated that these patients have prolonged bleeding times and their platelets failed to aggregate in response to activation. In the mid-1970s, Nurden and Caen[12] and Phillips and colleagues[13] discovered that thrombasthenic platelets are deficient in integrins αIIbβ3.