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PROS1 gene
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Gene

PROS1 gene

The PROS1 gene provides instructions for making protein S, a vital component in the regulation of blood clotting.

Normal Function

The PROS1 gene provides instructions for making a protein called protein S that is important for the regulation of blood clotting. Although protein S can work on its own to inhibit certain clotting factors, it often works as a cofactor. Cofactors enhance the function of proteins that speed up chemical reactions (enzymes).

Protein S is made by cells in the liver. The protein circulates in the bloodstream in two forms; it is either attached (bound) to a specific protein, or it occurs by itself in a free form. The free form of protein S can act as a cofactor for an enzyme called activated protein C (APC). APC turns off (inactivates) the blood clotting proteins known as factor Va and factor VIIIa. Protein S also helps a protein called tissue factor pathway inhibitor (TFPI) block the activity of another clotting protein, factor Xa. This inactivation slows down the clotting process so that blood flow is not impaired.

Health Conditions Related to Genetic Changes

Protein S deficiency

Hundreds of variants (also called mutations) in the PROS1 gene have been found to cause protein S deficiency. People with this condition have an increased risk of developing blood clots. Most of these variants change a single DNA building block (base pair) in the PROS1 gene.

Some variants in the PROS1 gene have been found to reduce the amount of available protein S. Other variants impair the function of protein S. Individuals with protein S deficiency may not have enough functional protein S to inactivate clotting proteins, which increases the risk of developing blood clots.

Other Names for This Gene

  • PROS
  • protein S, alpha
  • PS21
  • PS22
  • PS23
  • PS24
  • PS25
  • PSA
  • THPH5
  • THPH6
  • vitamin K-dependent plasma protein S

Frequently Asked Questions

Common signs include unexplained blood clots in veins or arteries, recurrent miscarriages, or a personal or family history of thrombosis. Some individuals remain asymptomatic until a provoking event such as surgery or pregnancy.
Blood tests measure total and free protein S activity and antigen levels. A low activity with normal antigen suggests a functional defect, while low antigen indicates a quantitative deficiency. Genetic testing of the PROS1 gene can confirm the specific mutation.
Yes. Pregnancy naturally lowers protein S levels, and women with a deficiency are at higher risk for venous thromboembolism and recurrent pregnancy loss. Prophylactic anticoagulation during pregnancy and the postpartum period is often recommended after consulting a hematologist.
nticoagulant therapy (e.g., warfarin, direct oral anticoagulants) is the mainstay for preventing clots. In high‑risk situations like pregnancy or major surgery, low‑molecular‑weight heparin may be used. Some patients also benefit from vitamin K antagonists with close INR monitoring.
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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