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A new congenital platelet abnormality characterized by spontaneous platelet
aggregation, enhanced von Willebrand factor platelet interaction, and the
presence of all von Willebrand factor multimers in plasma
A Casonato, L De Marco, M Mazzucato, V De Angelis, D De Roia, F Fabris, ZM Ruggeri and A Girolami
Centro Immunotrasfusionale e Chimica Clinica, Universita di Padov.
A case is reported of a 49-year-old woman with a mild bleeding tendency.
Her bleeding time, platelet count and size, plasma ristocetin cofactor
activity, von Willebrand factor (vWF) antigen, and vWF multimeric pattern
are all within normal limits. Spontaneous platelet aggregation is observed
when citrated platelet-rich plasma (PRP) is stirred in an aggregometer
cuvette. This aggregation is completely is only slightly diminished by an
antiglycoprotein (GP) IIb/IIIa or by an anti GPIb monoclonal antibody. The
patient's PRP shows increased sensitivity to ristocetin. The distinct
feature of this patient, also present in two family members studied, is
that platelet aggregation is initiated by purified vWF in the absence of
any other agonist. The vWF- induced platelet aggregation is abolished by
anti-GPIb and anti- GPIIb/IIIa monoclonal antibodies and by EDTA (5
mmol/L). Apyrase inhibits the second wave of aggregation. Patient's
platelets in PRP are four to six times more reactive to asialo vWF-induced
platelet aggregation than normal platelets. The amount of radiolabeled vWF
bound to platelets in the presence of either low concentration of
ristocetin or asialo vWF was increased 30% compared with normal. The
patient's platelet GPIb was analyzed by SDS page and immunoblotting and by
binding studies with anti-GPIb monoclonal antibodies showed one band with
slightly increased migration pattern and a normal number of GPIb molecules.
Unlike the previously reported patients with pseudo or platelet-type von
Willebrand disease, this patient has normal vWF parameters.
Volume 74,
Issue 6,
pp. 2028-2033,
11/01/1989
Copyright © 1989 by The American Society of Hematology
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