Von Willebrand Disease (vWd) Characterized by Increased Ristocetin Aggregation: A Study of Eleven Cases
The defective ristocetin aggregation occurring in patients with vWd is thought to depend on the decrease of a plasmatic factor related to factor VIII (Willebrand factor, VIIIVWF) 10 patients from 3 families had a mild to moderate bleeding tendency with autosomal dominant pattern of inheritance and laboratory findings suggestive for vWd (decreased levels of antihemophilic factor, and factor- VIII related antigen reduced platelet retention to glass beads columns and prolonged bleeding time). However, ristocetin aggregation in PRP was markedly increased, although VIIIVWF plasma levels were decreased. Aggregation induced in PRP by other agents (such as ADP, adrenaline and collagen), and the release of 14C serotonin was normal; the addition of purified bovine factor VIII was followed by normal aggregation in patients’ PRP and washed platelets. Patients’ washed platelets added to normal plasma aggregated to ristocetin more than normal washed platelets with patients’ plasma; the most marked aggregation response, however, was obtained when patients’ washed platelets were mixed with their own plasma. These findings suggest that a, platelet component is involved in the hyperaggregation response to ristocetin of these patients; however, the interaction of platelets with patients’ plasma is needed to produce the maximum response.Supported by a grant of the Fondazione Angelo Bianchi Bonomi.