VWF and hemophilia A: Human factor VIII (FVIII) functions as a cofactor for activated factor IX, and mutations in the FVIII gene (F8) result in hemophilia A. [1] FVIII in plasma is proteolyzed and/or pinocytosed unless it is protected by non-covalent binding to soluble forms of von Willebrand factor (VWF) multimers.