RESUMO
<p><b>OBJECTIVE</b>To study the platelet morphology and function of an inherited macrothrombocytopenia disorder with abnormal large granules.</p><p><b>METHODS</b>Platelet 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.</p><p><b>RESULTS</b>Both 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.</p><p><b>CONCLUSION</b>Both 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.</p>