Glanzmann's thrombasthenia

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.EDAR (EDAR hypohidrotic ectodermal dysplasia) 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 or acquired as an autoimmune disorder. The bleeding tendency in Glanzmann's thrombasthenia is variable, 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. Unidentified factors other than the platelet defect itself may have important roles. Glanzmann's thrombasthenia is associated with abnormal integrin αIIbβ3, formerly known as glycoprotein IIb/IIIa (GpIIb/IIIa), 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). In contrast, glycoproteinIb receptors are normal with Glanzmann's thrombasthenia. The role of GpIb is to enable platelet activation by contact with the von Willebrand factor-collagen complex that is exposed when the endothelial blood vessel lining is damaged. GpIb receptors are deficient in a disease known as Bernard–Soulier syndrome. 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.