Von Willebrand's disease is caused by a defect in the von Willebrand clotting factor, often accompanied by a deficiency of factor VIII as well.
Gene carriers for both forms of hemophilia can be detected through DNA studies in conjunction with results from factor VIII assays.
Hemophilia A is the most common type of coagulation disorder and involves decreased activity of factor VIII.
Individuals with less than 1 percent of normal factor VIII activity level have severe hemophilia.
Individuals with 1-5 percent of normal factor VIII activity level have moderate hemophilia and are at risk for heavy bleeding after seemingly minor traumatic injuries.