F8 and hemophilia A: This hypothesis is supported by the results of a comparison study of the properties of the proteolytic inhibitors in congenital hemophilia A and AHA, which, using proline-phenylalanine-arginine-methylcoumarinamide (PFR-MCA), a synthetic substrate for FVIII-hydrolyzing autoantibodies, revealed that the rate of FVIII hydrolysis differs significantly between hemophilia A and AHA patients.