Additional variant of type I von Willebrand disease.

We introduce a family with a von Willebrand subgroup that has not been described before. All of the eight subjects examined had normal levels of factor VIII coagulant activity (FVIII:C), a moderate reduction in the level of von Willebrand factor antigen (VWF:Ag), which resulted in a high FVIII:C/VWF:Ag ratio, and normal crossed immunoelectrophoresis, with normal multimeric pattern. The ristocetin cofactor in plasma and platelets was very low. Bleeding time was prolonged in two subjects without clearcut linkage to laboratory findings. In addition, an abnormality of platelet aggregation in response to ADP was observed: a decreased initial response was followed by marked disaggregation.