Heterogeneity of type I von Willebrand disease: evidence for a subgroup with an abnormal von Willebrand factor.

Type I von Willebrand disease (vWD) is characterized by equally low plasma concentrations of von Willebrand factor antigen (vWF  Ag) and ristocetin cofactor (RiCof) and by the presence of all vWF multimers in sodium dodecyl sulfate (SDS) -agarose gel electrophoresis.
For 17 patients (13 kindreds) diagnosed with these criteria, we have studied the platelet contents of vWF  Ag and RiCof and the changes of these in plasma after DDAVP infusion.
Platelet vWF  Ag and RiCof were normal in four kindreds (called " platelet normal " subgroup); following 1-deamino-8-D-arginine vasopressin; plasma vWF  Ag, RiCof and the bleeding time (BT) became normal.
In six kindreds, platelet vWF  Ag and RiCof were equally low (platelet low); after DDAVP, plasma vWF  Ag and RiCof remained low, and the BT was prolonged.
In three additional kindreds, platelets contained normal concentrations of vWF  Ag, but RiCof was very low (platelet discordant); even though a complete set of multimers was found in plasma and platelets, there was a relatively small amount of large multimers.
After DDAVP, plasma vWF  Ag became normal, but RiCof remained low and the BT was very prolonged.
These findings demonstrated that there can be an abnormal vWF (RiCof less than vWF  Ag) even in type I vWD, coexisting with a complete set of vWF multimers (platelet discordant); that the abnormal vWF can be shown more clearly in platelets than in plasma or else in plasma after DDAVP infusion; and that DDAVP normalizes the BT only in those patients with normal platelet levels of both vWF  Ag and RiCof (platelet normal).. 
