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


Reviewed February 2012

What is the official name of the FGB gene?

The official name of this gene is “fibrinogen beta chain.”

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

What is the normal function of the FGB gene?

The FGB gene provides instructions for making a protein called the fibrinogen B beta (Bβ) chain, one piece (subunit) of the fibrinogen protein. This protein is important for blood clot formation (coagulation), which is needed to stop excessive bleeding after injury. To form fibrinogen, the Bβ chain attaches to two other proteins called the fibrinogen A alpha (Aα) and fibrinogen gamma (γ) chains, each produced from different genes. Two sets of this three-protein complex combine to form functional fibrinogen.

For coagulation to occur, another protein called thrombin removes a piece from the Aα and the Bβ subunits of the functional fibrinogen protein (the pieces are called the A and B fibrinopeptides). This process converts fibrinogen to fibrin, the main protein in blood clots. Fibrin proteins attach to each other, forming a stable network that makes up the blood clot.

Does the FGB gene share characteristics with other genes?

The FGB gene belongs to a family of genes called endogenous ligands (endogenous ligands).

A gene family is a group of genes that share important characteristics. Classifying individual genes into families helps researchers describe how genes are related to each other. For more information, see What are gene families? ( in the Handbook.

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

congenital afibrinogenemia - caused by mutations in the FGB gene

Mutations in the FGB gene can lead to congenital afibrinogenemia, a condition that causes excessive bleeding due to the absence of fibrinogen protein in the blood. Most FGB gene mutations that cause this condition lead to an abnormally short blueprint for protein formation (mRNA). If any fibrinogen Bβ chain is produced, it is nonfunctional. Some mutations in the FGB gene result in the formation of a protein that cannot be released from the cell, making the protein effectively nonfunctional. Because this condition occurs when both copies of the FGB gene are altered, there is a complete absence of functional fibrinogen Bβ chain. Without the Bβ subunit, the fibrinogen protein is not assembled, which results in the absence of fibrin. As a result, blood clots do not form in response to injury, leading to excessive bleeding.

other disorders - caused by mutations in the FGB gene

Mutations in one or both copies of the FGB gene can cause other bleeding disorders known as hypofibrinogenemia, dysfibrinogenemia, or hypodysfibrinogenemia.

Hypofibrinogenemia is a condition characterized by decreased levels of fibrinogen in the blood. This condition is caused by mutations that reduce but do not eliminate the production of the fibrinogen Bβ chain. People with hypofibrinogenemia can have bleeding problems that vary from mild to severe. Generally, the less fibrinogen in the blood, the more severe the bleeding problems are.

Dysfibrinogenemia is a condition characterized by abnormally functioning fibrinogen, although the protein is present at normal levels. This condition is usually caused by mutations that change a single protein building block (amino acid) in the fibrinogen Bβ chain. These mutations alter the function of the fibrinogen protein and, depending on the functional change, can lead to excessive bleeding or abnormal blood clotting (thrombosis).

Hypodysfibrinogenemia is a condition characterized by low levels of abnormally functioning fibrinogen protein in the blood. As in dysfibrinogenemia, this condition can result in excessive bleeding or thrombosis.

Where is the FGB gene located?

Cytogenetic Location: 4q28

Molecular Location on chromosome 4: base pairs 154,562,980 to 154,572,763

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

The FGB gene is located on the long (q) arm of chromosome 4 at position 28.

The FGB gene is located on the long (q) arm of chromosome 4 at position 28.

More precisely, the FGB gene is located from base pair 154,562,980 to base pair 154,572,763 on chromosome 4.

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

Where can I find additional information about FGB?

You and your healthcare professional may find the following resources about FGB 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 FGB gene or gene products?

  • fibrinogen, B beta polypeptide
  • fibrinogen beta chain isoform 1 preproprotein
  • fibrinogen beta chain isoform 2 preproprotein

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

What glossary definitions help with understanding FGB?

amino acid ; blood clotting ; cell ; clotting ; coagulation ; congenital ; fibrin ; fibrinogen ; gene ; injury ; mRNA ; protein ; subunit ; thrombin ; thrombosis

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


  • Duga S, Asselta R, Santagostino E, Zeinali S, Simonic T, Malcovati M, Mannucci PM, Tenchini ML. Missense mutations in the human beta fibrinogen gene cause congenital afibrinogenemia by impairing fibrinogen secretion. Blood. 2000 Feb 15;95(4):1336-41. (
  • NCBI Gene (
  • Neerman-Arbez M. Molecular basis of fibrinogen deficiency. Pathophysiol Haemost Thromb. 2006;35(1-2):187-98. Review. (
  • Vu D, Di Sanza C, Caille D, de Moerloose P, Scheib H, Meda P, Neerman-Arbez M. Quality control of fibrinogen secretion in the molecular pathogenesis of congenital afibrinogenemia. Hum Mol Genet. 2005 Nov 1;14(21):3271-80. Epub 2005 Sep 29. (
  • Weisel JW. Fibrinogen and fibrin. Adv Protein Chem. 2005;70:247-99. 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: February 2012
Published: February 8, 2016