This mutation is a novel variation which has not been reported either in the Hemophilia B Mutation Database (http://www.factorix.org/; Thompson & Chen, 1993) or the Human Gene Mutation Database (HGMD, http://www.hgmd.cf.ac.uk/ac/index.php), although a 31095A>C variation has been reported in HGMD leading to a Y371S mutation causing mild HB (20% of normal FIX activity). Here, F9 is linked to hemophilia B.