PARTIAL EXPRESSION OF GP-IB MEASURED BY FLOW-CYTOMETRY IN 2 PATIENTS WITH BERNARD-SOULIER-SYNDROME

Bernard-Soulier syndrome is a rare, congenital bleeding disorder cause d by absent or defective GP Ib platelet membrane receptor for the von Willebrand factor (vWF). We studied two brothers with moderate bleedin g symptoms. Bleeding time was prolonged and ristocetin-induced platele t aggregation was absent. Flow cytometric analysis showed that both bo ys had a subnormal expression of GP Ib. One antibody used (AN51) was b ound only to 30% of the platelets and at a subnormal density. A second antibody (SZ2) also bound at a subnormal density but a normal fractio n of the platelets were immunoreactive. Ristocetin stimulation of the patients' platelets in the presence of plasma resulted in a low bindin g of VWF, about 30% of healthy controls. On the other hand the express ion of GP IIb/IIIa on the platelet membrane appeared to be supernormal even when the increased platelet size was taken into account as shown by the ratio between the density of GP IIIa and CD 9 structures. We c onclude that these brothers have a variant of the Bernard-Soulier synd rome with a low expression of a GP Ib receptor.