VON WILLEBRAND'S DISEASE TYPE IIB ASSOCIATED TO A COMPLEX THROMBOCYTOPENIC THROMBOCYTOPATHY

A family bleeding disorder characterized by a new association between Type IIB von Willebrand's disease (vWD) and a complex platelet disfunction, with an intermittent thrombocytopenia is described in two patients from the same generation. The mother and a maternal aunt died having severe bleeding diathesis. The platelet abnormalities included: borderline or slightly low platelet count but moderate thrombocytopenia coincedent with the acute bleeding episodes, giant platelet site with a very heterogeneous distribution width, large number of vesicles in platelets by electron-microscopy recalling the "Swiss-Cheese" platelets, abnormal platelet aggregation induced by ADP, collagen, epinephrin and slightly, by thrombin, defective release of ¹⁴C-Serotonin, von Willebrand factor (vWF) and platelet factor 4 induced by thrombin or ADP. DDAVP was given to both patient and a partial and transitory correction of bleeding time, thrombocytopenia, presence of platelet aggregates on smear besides a brief appearence of larger multimers of vWF and an increase in all Factor VIII/von Willebrand Factor (FVIII/vWF) properties were seen. Binding of labeled vWF using radiolabelled monoclonal anti-vWF antibody showed an enhanced binding of the patients' vWF, induced by ristocetin, to either normal or patients' platelets. In contrast, the binding of labeled purified normal vWF induced by thrombin to patients' platelets was decreased as compared with the correspondent control. Thus, both patients have platelet disfunctions characteristic for more than one specific platelet disorder. Several associations between platelet and FVIII/vWF abnormalities have been described. This is the first family presenting association of Type IIB vWD and a complex thrombocytopathy. The inherited or acquired (induced by the abnormal IIB vWF platelet interaction) nature of the abnormality is discussed.