Summary
Von Willebrand disease is characterised by a quantitative (type 1) or qualitative
(type 2) decrease in von Willebrand factor (vWF) a multimeric glycoprotein involved
in primary haemostasis. The propep-tide of von Willebrand, also named vWF antigen
II (vWF:AgII), is released from platelets and endothelial cells and circulates in
plasma as a glycoprotein of 100 kD. In the present study, we attempted to determine
whether vWF:AgII level may provide information on the synthesis of vWF, specially
in patients with von Willebrand disease (vWD). To elucidate that point, we developed
an ELISA and quantify the vWF:AgII in normal individuals and in various vWD patients.
The propeptide molar concentration was found to be 5nM as compared to 31 nM for mature
vWF. In normal individuals, the level of vWF:AgII was significantly decreased in females
from O and A blood groups. In type 2 vWD patients the level of plasma vWF:AgII appears
normal in the patients with normal level of platelet vWF. In type 2 B vWD characterised
by increased affinity of mature vWF for platelet glyco-protein Ib, the vWF:Ag II in
contrast to the vWF antigen (vWF:Ag) was not decreased. In type 2A vWD patients the
level of vWF:AgII was decreased in patients with absence of high molecular weight
vWF in platelets and plasma but normal in patients with increased sensitivity to proteolysis.
Finally, in type 1 vWD, some studied patients have a parallel decrease in vWF:AgII
and vWF:Ag whereas in others, the vWF:Ag levels were much more affected than corresponding
vWF:AgII levels, as observed in some type 2 vWD patients. Thus, in contrast to that
already described, the plasma vWF:AgII level cannot discriminate type 1 from type
2 vWD patients. We conclude that the vWF:AgII measurement provides additional information
on the mechanisms responsible for vWD and might also contribute to the classification
of vWD patients.
