Concurrence of von Willebrand's disease and hemophilia A: implications for carrier detection and prevalence.

Five families with concurrent von Willebrand's disease (VWD) and classic hemophilia (hemophilia A) are described. Three were ascertained through women undergoing hemophilia carrier testing, one through an obligate carrier who also has VWD, and one through the affected father of a hemophiliac. The VWD probands exhibited Type I VWD with reduced Factor VIII-related antigen (VIIIR:Ag) and/or von Willebrand factor on more than one occasion, normal VIIIR:Ag on crossed immunoelectrophoresis, and mild symptoms. No male had both disorders, but two obligate hemophilia carriers also had VWD. Neither was detectable as a carrier by discriminant analysis. Four possible carriers of hemophilia had VWD and would also be classified as noncarriers statistically. These findings suggest that the presence of VWD may invalidate hemophilia carrier testing by conventional methods. The independent entry into the family of the two genes by mating of a hemophilia carrier and a VWD male is documented in two cases and probable in two. The observed frequency of such matings supports the hypothesis that VWD is a common disorder.