BERNARD-SOULIER SYNDROME - QUANTITATIVE CHARACTERIZATION OF MEGAKARYOCYTES AND PLATELETS BY BOW CYTOMETRIC AND PLATELET KINETIC MEASUREMENTS

Platelets and megakaryocytes have been characterized in a Bernard-Soul ier syndrome (BSS) kindred with respect to glycoprotein (GP) membrane receptors and measurements of thrombocytopoiesis. The index patient ex hibited lifelong bleeding tendency, moderate thrombocytopenia (35 x 10 (9)/l), giant platelets (mean platelet volume 12.5 mu m(3) compared to 7.5 +/- 1.5 mu m(3) in normals), absent ristocetin-induced platelet a gglutination and absent binding of von Willebrand factor (VWF). Flow-c ytometric analysis revealed absent platelet binding (0-2%) of monoclon al antibodies (mAb, LJ-P3, LJ-Ib1 and LJ-Ib 10) directed against disti nct epitopes on membrane GPIb alpha of the GPIb-IX complex, and normal binding of LJ-P4 mAb directed against GPIIb/IIIa complex (relative to increased platelet surface area). Marrow megakaryocytes also failed t o express GPIb-IX complex, but demonstrated normal expression of GPIIb /IIIa. Among 6 asymptomatic family members, the patient's mother and 2 of his 4 children exhibited approximately 50% binding of anti-GPIb al pha mAb to their platelets by both flow cytometry and direct binding s tudies using I-125-vWF, I-125-LJ-Ib1 and I-125-LJ-Ib10 mAb. Marrow meg akaryocytes were increased in the average cell volume and cytoplasmic granularity with a corresponding increase in ploidy (46% > 16N compare d to 22 +/- 5% in normal individuals), a pattern typical of megakaryoc ytes stimulated by thrombocytopenia. Autologous In-111-platelet life s pan was shortened to 4.1 days (compared with 9.5 +/- 0.5 days in norma l subjects), and the turnover of platelet mass in the circulation was near normal. The data directly demonstrate that the platelet membrane GPIb-IX defect in BSS originates in megakaryocytes at all levels of ce ll maturation, and exclude the possibility that the receptor abnormali ty is acquired during cell maturation or after platelets are released into the circulation. Since marrow megakaryocytes exhibited cellular c hanges consistent with stimulated megakaryocytopoiesis, these results also suggest that thrombocytopenia in this kindred of BS S is a conseq uence of both decreased platelet survival and ineffective platelet pro duction.