Autosomal dominant macrothrombocytopenia

Autosomal dominant macrothrombocytopenia is a group of inherited bleeding disorders characterized by a reduced number of platelets (thrombocytopenia) that are abnormally large in size (macrothrombocytes or giant platelets). The condition primarily affects the blood and hemostatic system. Because platelets play a critical role in blood clotting, affected individuals may experience mild to moderate bleeding symptoms, including easy bruising, prolonged bleeding from cuts or dental procedures, nosebleeds (epistaxis), and in some cases heavy menstrual bleeding (menorrhagia) in women. The severity of bleeding symptoms can vary considerably, even among members of the same family, and some individuals may be largely asymptomatic despite having low platelet counts. This condition encompasses several distinct genetic entities that share the hallmark features of dominantly inherited thrombocytopenia with large platelets. These include disorders caused by mutations in genes such as MYH9 (MYH9-related disease, which includes May-Hegglin anomaly, Sebastian syndrome, Fechtner syndrome, and Epstein syndrome), GP1BA, TUBB1, ACTN1, and others. Some subtypes may be associated with additional features beyond bleeding, such as sensorineural hearing loss, nephritis, cataracts, or inclusion bodies in white blood cells, depending on the specific genetic cause. Diagnosis is often made through a combination of complete blood count showing thrombocytopenia with elevated mean platelet volume, peripheral blood smear examination revealing giant platelets, family history consistent with autosomal dominant inheritance, and increasingly through genetic testing. It is important that this condition is correctly identified, as patients are frequently misdiagnosed with immune thrombocytopenic purpura (ITP) and may receive unnecessary treatments such as corticosteroids or splenectomy. Treatment is generally supportive and includes avoidance of antiplatelet medications, management of bleeding episodes with platelet transfusions or desmopressin (DDAVP) when needed, and appropriate precautions before surgical or dental procedures. For most patients, the prognosis is favorable, though monitoring for associated complications (such as renal disease or hearing loss in MYH9-related disorders) may be warranted depending on the underlying genetic cause.

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