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

FGB gene

The FGB gene provides instructions for a subunit of the fibrinogen protein, which is essential for blood clot formation and stopping excessive bleeding.

Normal Function

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. 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. This process converts fibrinogen to fibrin, the main protein in blood clots, which forms a stable network.

Health Conditions Related to Genetic Changes

Congenital afibrinogenemia

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 result in a protein that cannot be released from the cell.
  • Because this condition occurs when both copies of the FGB gene are altered, there is a complete absence of functional fibrinogen Bβ chain, preventing the assembly of fibrinogen and the formation of fibrin.

Other disorders

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

  • Hypofibrinogenemia: Characterized by decreased levels of fibrinogen in the blood, caused by mutations that reduce but do not eliminate the production of the fibrinogen Bβ chain.
  • Dysfibrinogenemia: Characterized by abnormally functioning fibrinogen present at normal levels, usually caused by mutations that change a single amino acid in the Bβ chain. This can lead to excessive bleeding or abnormal blood clotting (thrombosis).
  • Hypodysfibrinogenemia: 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

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

Frequently Asked Questions

Diagnosis typically involves blood tests to measure fibrinogen levels and assess clotting function. For congenital afibrinogenemia, fibrinogen levels will be undetectable or extremely low. For hypofibrinogenemia, levels will be decreased but still present. Genetic testing of the FGB gene can then confirm the specific mutations causing the condition, which is crucial for definitive diagnosis and family planning.
The primary treatment involves replacing the missing or deficient fibrinogen. This is usually done through infusions of fibrinogen concentrate or fresh frozen plasma (FFP) to provide the necessary clotting protein. Treatment is often given on demand to stop bleeding episodes or preventatively before surgeries or procedures that carry a high risk of bleeding. Regular monitoring of fibrinogen levels and close collaboration with a hematologist are essential.
Congenital afibrinogenemia is inherited in an autosomal recessive pattern. This means a child must inherit two altered copies of the FGB gene (one from each parent) to develop the condition. If both parents are carriers (each having one altered gene copy), there is a 25% chance with each pregnancy that their child will have congenital afibrinogenemia, a 50% chance they will be a carrier, and a 25% chance they will not inherit any altered genes. Hypofibrinogenemia can sometimes occur with only one altered gene copy, but the severe form (afibrinogenemia) requires two. Genetic counseling is highly recommended for families with a known history.
Congenital afibrinogenemia, due to FGB gene mutations, often presents with symptoms of excessive bleeding. In newborns, this might include bleeding from the umbilical cord stump, easy bruising, or prolonged bleeding after minor injuries or circumcision. Later in life, individuals may experience nosebleeds, gum bleeding, heavy menstrual bleeding, joint bleeding (hemarthrosis), or internal bleeding. The severity can vary, but the key feature is a tendency for uncontrolled bleeding.
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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