An inherited macrothrombocytopenic disorder with abnormal large granules

Inherited giant platelet syndromes are a heterogeneous group of rare bleeding disorders. In the current study, a patient was reported with prolonged bleeding time, thrombocytopenia and giant platelets. Both the patient's red and white cell counts were normal without morphological abnormalities. The electron microscopy of platelets showed abnormal large electron-dense granules in the cytoplasm with exocytosis being easily observed. Her fathers platelets had the same abnormalities. The expression of glycoprotein (GP)Ib, GPIIb and GPIIIa on the surface of the patient's platelets was normal, and her platelet aggregation in response to ADP and ristocetin was also normal. Immunogold probes combined to monoclonal antibodies against GPIIIa, P-selectin or CD63 could not identify any relationship between the aberrant structures and alpha granules or lysosomes of platelet. Serotonin level was normal in the platelets of the patient, indicating the electron opaque granules are not dense bodies. The morphological abnormalities of the platelets from the patient are clearly distinguishable from other hereditary giant platelet disorders. We propose that the abnormal large granules from the patient's platelets probably represent a novel inherited thrombocytopenic disorder.