Reviewed March 2007
What is the official name of the F9 gene?
The official name of this gene is “coagulation factor IX (plasma thromboplastic component, Christmas disease, hemophilia B).”
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 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 an enzyme 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 XI. 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?
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hemophilia - caused by mutations in the F9 gene
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Mutations in the F9 gene cause a type of hemophilia called hemophilia B. Hundreds of 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. The altered protein cannot participate effectively in the blood clotting process and, in some cases, the protein does not work at all. A shortage of this protein prevents blood clots from forming 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 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
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Several mutations in the F9 gene cause an increased sensitivity 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. The mutations responsible for warfarin hypersensitivity each change a single base pair in the F9 gene. Although people with these mutations do not have hemophilia B, they develop similar problems with blood clotting if 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.
Where is the F9 gene located?
Cytogenetic Location: Xq27.1-q27.2
Molecular Location on the X chromosome: base pairs 138,440,560 to 138,473,282
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 138,440,560 to base pair 138,473,282 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.
- PubMed
- Recent literature
- OMIM
- Genetic disorder catalog
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What other names do people use for the F9 gene or gene products?
- Christmas factor
- coagulation factor IX
- FA9_HUMAN
- Factor 9
- FIX
- HEMB
- Plasma thromboplastin component
- PTC
Where can I find general information about genes?
The Handbook provides basic information about genetics in clear language.
These links provide additional genetics resources that may be useful.
What glossary definitions help with understanding F9?
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.