The lack of the procoagulant protein factor VIII (FVIII) for hemophilia A or the serine protease‐precursor factor IX (FIX) for hemophilia B affects 1–2 per 10,000 and 1 per 25,000 males at birth, respectively (Bolton‐Maggs & Pasi, 2003). The gene discussed is F9; the disease is hemophilia B.