F9

About F9

F9 on chromosome Xq27.1 encodes coagulation factor IX, a vitamin K dependent serine protease that, once activated, forms a complex with factor VIII to activate factor X in the clotting cascade. Variants that reduce or abolish factor IX activity cause hemophilia B, also called Christmas disease after Stephen Christmas, the first patient described with it in 1952. Because the gene is on the X chromosome, hemophilia B mainly affects males, while female carriers may have mild bleeding symptoms. Severity correlates with residual factor activity and ranges from bleeding only after surgery or injury to spontaneous bleeding into joints and muscles. Genetic analysis of Romanov family remains in 2009 showed that the royal disease carried by descendants of Queen Victoria was hemophilia B. Gene therapy using AAV vectors to deliver F9 has received regulatory approval.