血小板凝集において易反応性を示す非定型的ｖｏｎ Ｗｉｌｌｅｂｒａｎｄ病の１家系

Abstract

Two family members (daughter and mother) with a bleeding disorder showed prolonged bleeding time and activated partial thromboplastin time associated with decreased plasma levels of factor VIII procoagulant activity, factor VIII-related antigen and von Willebrand factor (vWf). The ristocetin-induced platelet agglutination was enhanced, but collagen- and Ca ionophore-induced platelet aggregation were also increased at their low concentrations. Contrary to the type II B von Willebrand's disease (vWd), pseudo-vWd and platelet-type vWd, they did not show any increased binding of factor VIII/vWf to platelets in the presence of ristocetin. In addition, when a small amount of normal plasma was added to the washed platelets suspension at a sufficient concentration of ristocetin and when a low concentration of ristocetin was added to the washed platelets suspension at a sufficient amount of normal plasma, their platelets were more aggregated than normal platelets. In this atypical vWd, therefore, the hyper-reactivity of platelet aggregation may be due to an intrinsic platelet abnormalitiy, not due to enhanced interaction between plasma factor VIII/vWf and platelets.