Giant platelet syndrome

Platelets are small, disk-shaped, anuclear cells with a mean diameter of 2 to 3 mm. They are derived from cytoplasmic fragmentation of megakaryocytes, released into the circulation and survived for 7 /10 days. Megakaryocyte development and platelet formation are regulated by thrombopoietin and other cytokines. It is now generally assumed that platelets are released by extension and fragmentation of cytoplasmic processes (proplatelet) of megakaryocytes through sinus endothelial cells in the bone marrow. It is not known, however, how the number and the size of the platelet are controlled at this step [1]. Giant platelet syndrome is a group of unique disorders characterized by the presence of abnormally large platelets, and is usually accompanied by thrombocytopenia. Thus, it is also called macrothrombocytopenia. Giant platelets are occasionally observed as an incidental finding in routine blood smear examinations. Most of them are due to acquired disorders such as idiopathic thrombocytopenic purpura (ITP) and myelodysplastic syndrome (MDS) (Table I). In contrast, inherited giant platelet disorders are rare. The mechanisms of giant platelet formation and thrombocytopenia are not fully understood in both inherited and acquired disorders. It is important from a clinical standpoint that congenital disorders are distinguished from acquired disorders, especially ITP, to avoid unnecessary treatments. We will discuss the molecular basis, diagnosis, and management of some major inherited giant platelet syndromes.