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F8 gene
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Gene

F8 gene

The F8 gene provides instructions for making coagulation factor VIII, a protein that is essential for the formation of blood clots following an injury.

Normal Function

The F8 gene provides instructions for making a protein called coagulation factor VIII. 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 VIII is made chiefly by cells in the liver. This protein circulates in the bloodstream in an inactive form, bound to another molecule called von Willebrand factor, until an injury that damages blood vessels occurs. In response to injury, coagulation factor VIII is activated and separates from von Willebrand factor. The active protein (sometimes written as coagulation factor VIIIa) interacts with another coagulation factor called factor IX. This interaction sets off a chain of additional chemical reactions that form a blood clot.

Health Conditions Related to Genetic Changes

Hemophilia

Mutations in the F8 gene cause hemophilia A, the most common form of this bleeding disorder. More than 1,300 alterations in this gene have been identified. Mutations in the F8 gene lead to the production of an abnormal version of coagulation factor VIII or reduce the amount of this protein, meaning blood clots cannot form properly in response to injury.

Key points regarding these mutations include:

  • Types of mutations: These include changes to single DNA building blocks (base pairs), deletions, or insertions.
  • Inversions: The most common mutation in people with severe hemophilia A is a rearrangement of genetic material called an inversion, which involves a large segment of the F8 gene.
  • Severity: Mutations that almost completely eliminate the activity of coagulation factor VIII result in severe hemophilia, while others that reduce but do not eliminate activity result in mild or moderate hemophilia.

Frequently Asked Questions

Yes, hemophilia A is an X-linked recessive disorder. A mother can be a carrier, meaning she has one normal X chromosome and one X chromosome with the F8 mutation. She may have normal or near-normal factor VIII levels and no symptoms, but she has a 50% chance of passing the mutated gene to a son, who would then have hemophilia A, and a 50% chance of passing it to a daughter, who would become a carrier. Genetic testing can confirm carrier status for women in families with a history of the condition.
Inhibitors are antibodies that the immune system produces against factor VIII, neutralizing its ability to form clots. They develop in approximately 20-30% of patients with severe hemophilia A. Once inhibitors are present, standard factor VIII replacement therapy becomes ineffective, leading to difficult-to-control bleeding. Treatment shifts to bypassing agents (such as emicizumab or rFVIIa) or immune tolerance induction (ITI) to eliminate the antibodies. Regular monitoring for inhibitor development is a critical part of managing severe hemophilia A.
When administered intravenously, factor VIII concentrate acts rapidly, often within minutes to hours. The effectiveness is monitored clinically by the cessation of bleeding and the stabilization of the affected area (e.g., reduced swelling in a joint). Laboratory monitoring of factor VIII levels can also confirm that therapeutic levels have been reached. If bleeding persists despite appropriate dosing, it may indicate the presence of inhibitors (antibodies against factor VIII) or an incorrect diagnosis, requiring immediate medical evaluation.
The severity is classified by factor VIII activity levels. Severe hemophilia A (less than 1% activity) involves spontaneous bleeding into joints and muscles, requiring regular prophylactic treatment. Moderate hemophilia A (1% to 5% activity) typically causes bleeding only after minor trauma or surgery. Mild hemophilia A (5% to 40% activity) often goes undiagnosed until a significant injury or surgery reveals prolonged bleeding. Daily life for those with severe hemophilia requires strict avoidance of contact sports and consistent adherence to factor replacement therapy, while those with mild cases may only need treatment during acute bleeding events.
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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