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FGG gene
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Gene

FGG gene

The FGG gene provides instructions for making the fibrinogen gamma chain, a protein subunit essential for blood clot formation.

Normal Function

The FGG gene provides instructions for making the fibrinogen gamma (γ) 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 γ chain attaches to the fibrinogen A alpha (Aα) and fibrinogen B beta (Bβ) 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.

Health Conditions Related to Genetic Changes

Congenital afibrinogenemia

Mutations in the FGG gene can lead to congenital afibrinogenemia, a condition that causes excessive bleeding due to the absence of fibrinogen protein in the blood. Most FGG gene mutations that cause this condition lead to an abnormally short blueprint for protein formation (mRNA). If any fibrinogen γ chain is produced, it is nonfunctional. Because this condition occurs when both copies of the FGG gene are altered, there is a complete absence of functional fibrinogen γ chain. Without the γ 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 the excessive bleeding seen in people with congenital afibrinogenemia.

Other disorders

Mutations in one or both copies of the FGG gene can cause other bleeding disorders:

  • Hypofibrinogenemia: A condition characterized by decreased levels of fibrinogen in the blood. This is caused by mutations that reduce but do not eliminate the production of the fibrinogen γ chain. Bleeding problems vary from mild to severe; generally, the less fibrinogen in the blood, the more severe the bleeding.
  • Dysfibrinogenemia: A condition characterized by abnormally functioning fibrinogen, although the protein is present at normal levels. This is usually caused by mutations that change a single protein building block (amino acid) in the fibrinogen γ chain, which can lead to excessive bleeding or abnormal blood clotting (thrombosis).
  • Hypodysfibrinogenemia: A condition characterized by low levels of abnormally functioning fibrinogen protein in the blood, which can result in excessive bleeding or thrombosis.

Other Names for This Gene

  • FIBG_HUMAN
  • fibrinogen gamma chain isoform gamma-A precursor
  • fibrinogen gamma chain isoform gamma-B precursor
  • fibrinogen, gamma polypeptide

Frequently Asked Questions

Cesarean sections carry a higher risk of significant bleeding in individuals with afibrinogenemia due to the lack of clotting ability. However, they can be performed safely if the patient is pre-treated with fibrinogen concentrate or cryoprecipitate to raise blood levels to a safe range before surgery. Close monitoring by a hematologist and anesthesiologist is essential to manage potential bleeding complications during and after the procedure.
The most common early sign is severe bleeding from the umbilical cord stump after birth, which may persist for several days. Other early indicators include excessive bruising, bleeding from the mouth or nose, and prolonged bleeding from minor cuts. In severe cases, intracranial hemorrhage (bleeding in the brain) can occur, which is a medical emergency requiring immediate attention.
Standard prothrombin time (PT) and activated partial thromboplastin time (aPTT) tests are often prolonged in afibrinogenemia, but a specific fibrinogen activity test is required for confirmation. This test measures the functional level of fibrinogen in the blood. In congenital afibrinogenemia, the result is typically undetectable or extremely low. Genetic testing of the FGG gene can then confirm the diagnosis by identifying specific mutations that prevent the production of the fibrinogen gamma chain.
Yes, with proper management, individuals can lead normal, active lives. Treatment involves replacing the missing fibrinogen using fibrinogen concentrate or cryoprecipitate, especially before surgeries, dental work, or during episodes of significant bleeding. Regular monitoring by a hematologist is necessary to adjust dosages and prevent complications such as blood clots (thrombosis), which can occur if fibrinogen levels are raised too high or too quickly.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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