OBJECTIVETo study the platelet morphology and function of an inherited macrothrombocytopenia disorder with abnormal large granules.

METHODSPlatelet size and structure were investigated by both light microscopy and electron microscopy. The platelet membrane expression of GP I b, GP II b, GPIII a, P-selectin and CD63 were analyzed by using respective monoclonal antibodies. Platelet 5-hydroxy-tryptamine was measured with spectrophotofluorometer.

RESULTSBoth the patient and her father had large granules in their platelets, with exocytosis being easily observed. The expressions of GP I b, GP II b and GP II a on the platelets were in normal range, while P-selectin and CD63 were somewhat increased. The abnormal large granules were not the alpha granules, lysosomes or dense bodies.

CONCLUSIONBoth morphological and functional abnormalities of the platelets from the patient are clearly distinguishable from other hereditary giant platelet disorders. It would probably represent a novel platelet disorder.