From the blood coagulation state testing of mother II-2’s first children affected with hemophilia A and 4479405 (Figures 1B, 3D), we can see that not only factor VIII decreased but also factor IX apparently declined, which is responsible for hemophilia B. FIX is a serine protease that plays a vital role in the coagulation cascade. The gene discussed is F9; the disease is hemophilia A.