Hemophilia is an inherited bleeding disorder in which the blood does not clot properly, causing affected individuals to experience spontaneous bleeding as well as bleeding after injuries or surgery. The 2 most common types are hemophilia A, caused by low levels of clotting factor VIII; and hemophilia B, caused by low levels of clotting factor IX. The standard treatment for hemophilia involves replacing the missing blood clotting factor by infusing commercially prepared factor concentrates.