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Genetics Home Reference: your guide to understanding genetic conditions     A service of the U.S. National Library of Medicine®


Reviewed May 2010

What is the official name of the F9 gene?

The official name of this gene is “coagulation factor IX.”

F9 is the gene's official symbol. The F9 gene is also known by other names, listed below.

What is the normal function of the F9 gene?

The F9 gene provides instructions for making a protein called coagulation factor IX. Coagulation factors are a group of related proteins that are essential for the formation of blood clots. After an injury, clots protect the body by sealing off damaged blood vessels and preventing further blood loss.

Coagulation factor IX is made in the liver. This protein circulates in the bloodstream in an inactive form until an injury that damages blood vessels occurs. In response to injury, coagulation factor IX is activated by another coagulation factor called factor XIa. The active protein (sometimes written as coagulation factor IXa) interacts with coagulation factor VIII and other molecules. These interactions set off a chain of additional chemical reactions that form a blood clot.

How are changes in the F9 gene related to health conditions?

hemophilia - caused by mutations in the F9 gene

Mutations in the F9 gene cause a type of hemophilia called hemophilia B. More than 900 alterations in this gene have been identified. The most common mutations change single DNA building blocks (base pairs) in the gene. A small percentage of mutations delete or insert multiple base pairs or rearrange segments of DNA within the gene.

Mutations in the F9 gene lead to the production of an abnormal version of coagulation factor IX or reduce the amount of this protein. The altered or missing protein cannot participate effectively in the blood clotting process. As a result, blood clots cannot form properly in response to injury. These problems with blood clotting lead to excessive bleeding that can be difficult to control. Mutations that completely eliminate the activity of coagulation factor IX result in severe hemophilia. Mutations that reduce but do not eliminate the protein's activity usually cause mild or moderate hemophilia.

Several mutations near the beginning of the F9 gene sequence cause an unusual form of hemophilia known as hemophilia B Leyden. People with these mutations are born with very low levels of functional coagulation factor IX, but hormonal changes cause the levels of this protein to increase gradually during puberty. As a result, adults with hemophilia B Leyden rarely experience episodes of abnormal bleeding.

other disorders - caused by mutations in the F9 gene

Several rare mutations in the F9 gene cause an increased sensitivity (hypersensitivity) to a drug called warfarin. This medication is an anticoagulant, which means it is used to prevent the formation or growth of abnormal blood clots. Warfarin works by reducing the amount of active factor IX and three other coagulation proteins.

The mutations responsible for warfarin hypersensitivity each change a single base pair in the F9 gene. These mutations do not cause hemophilia B, and people with these genetic changes only have bleeding problems if they are treated with warfarin. Warfarin reduces the amount of coagulation factor IX to very low levels in these individuals, which prevents the blood from clotting normally and can lead to recurrent, severe bleeding problems. To avoid these complications, people with warfarin hypersensitivity can be treated with other anticoagulant medications.

Where is the F9 gene located?

Cytogenetic Location: Xq27.1-q27.2

Molecular Location on the X chromosome: base pairs 139,530,734 to 139,563,464

(Homo sapiens Annotation Release 107, GRCh38.p2) (NCBI (

The F9 gene is located on the long (q) arm of the X chromosome between positions 27.1 and 27.2.

The F9 gene is located on the long (q) arm of the X chromosome between positions 27.1 and 27.2.

More precisely, the F9 gene is located from base pair 139,530,734 to base pair 139,563,464 on the X chromosome.

See How do geneticists indicate the location of a gene? ( in the Handbook.

Where can I find additional information about F9?

You and your healthcare professional may find the following resources about F9 helpful.

You may also be interested in these resources, which are designed for genetics professionals and researchers.

What other names do people use for the F9 gene or gene products?

  • Christmas factor
  • coagulation factor IX (plasma thromboplastic component, Christmas disease, hemophilia B)
  • Factor 9
  • FIX
  • HEMB
  • Plasma thromboplastin component
  • PTC

See How are genetic conditions and genes named? ( in the Handbook.

What glossary definitions help with understanding F9?

base pair ; blood clotting ; clotting ; coagulation ; coagulation factors ; DNA ; gene ; hemostasis ; injury ; plasma ; protein ; puberty ; sensitivity ; warfarin

You may find definitions for these and many other terms in the Genetics Home Reference Glossary.


  • Bolton-Maggs PH, Pasi KJ. Haemophilias A and B. Lancet. 2003 May 24;361(9371):1801-9. Review. (
  • Bowen DJ. Haemophilia A and haemophilia B: molecular insights. Mol Pathol. 2002 Apr;55(2):127-44. Review. Erratum in: Mol Pathol 2002 Jun;55(3):208. (
  • Chu K, Wu SM, Stanley T, Stafford DW, High KA. A mutation in the propeptide of Factor IX leads to warfarin sensitivity by a novel mechanism. J Clin Invest. 1996 Oct 1;98(7):1619-25. (
  • Giangrande P. Haemophilia B: Christmas disease. Expert Opin Pharmacother. 2005 Aug;6(9):1517-24. Review. (
  • Kristensen SR. Warfarin treatment of a patient with coagulation factor IX propeptide mutation causing warfarin hypersensitivity. Blood. 2002 Oct 1;100(7):2676-7. (
  • Lillicrap D. The molecular basis of haemophilia B. Haemophilia. 1998 Jul;4(4):350-7. Review. (
  • NCBI Gene (
  • Oldenburg J, Kriz K, Wuillemin WA, Maly FE, von Felten A, Siegemund A, Keeling DM, Baker P, Chu K, Konkle BA, Lämmle B, Albert T; Study Group on Hereditary Warfarin Sensitivity. Genetic predisposition to bleeding during oral anticoagulant therapy: evidence for common founder mutations (FIXVal-10 and FIXThr-10) and an independent CpG hotspot mutation (FIXThr-10). Thromb Haemost. 2001 Mar;85(3):454-7. (
  • Oldenburg J, Quenzel EM, Harbrecht U, Fregin A, Kress W, Müller CR, Hertfelder HJ, Schwaab R, Brackmann HH, Hanfland P. Missense mutations at ALA-10 in the factor IX propeptide: an insignificant variant in normal life but a decisive cause of bleeding during oral anticoagulant therapy. Br J Haematol. 1997 Jul;98(1):240-4. (
  • Ulrich S, Brand B, Speich R, Oldenburg J, Asmis L. Congenital hypersensitivity to vitamin K antagonists due to FIX propeptide mutation at locus -10: a (not so) rare cause of bleeding under oral anticoagulant therapy in Switzerland. Swiss Med Wkly. 2008 Feb 23;138(7-8):100-7. doi: 2008/07/smw-12022. (
  • Zögg T, Brandstetter H. Activation mechanisms of coagulation factor IX. Biol Chem. 2009 May-Jun;390(5-6):391-400. doi: 10.1515/BC.2009.057. Review. (


The resources on this site should not be used as a substitute for professional medical care or advice. Users seeking information about a personal genetic disease, syndrome, or condition should consult with a qualified healthcare professional. See How can I find a genetics professional in my area? ( in the Handbook.

Reviewed: May 2010
Published: February 1, 2016