Protein S is a specialized protein found in the bloodstream that plays a significant role in regulating blood clotting. It functions as a natural anticoagulant, preventing excessive blood clot formation while ensuring blood can clot when needed. Maintaining appropriate levels is important for the delicate balance of the coagulation system.
What Protein S Does
Protein S acts as a cofactor for activated protein C (APC), another protein that controls blood coagulation. Together, Protein S and APC inactivate specific clotting factors, Factor Va and Factor VIIIa, which are essential for blood clotting. This inactivation slows the rate of clot formation. When Protein S levels are low or its function is impaired, this natural anticoagulant pathway weakens. A deficiency increases the risk of developing abnormal blood clots, particularly venous thromboembolism (VTE).
Protein S Deficiency from Acquired Conditions
Protein S deficiency can develop due to underlying medical conditions or circumstances, rather than being inherited. This acquired form is often temporary. When the condition causing the deficiency is successfully treated or resolves, Protein S levels can return to their normal range, meaning the deficiency effectively “goes away.”
Several factors can lead to an acquired deficiency. These include liver disease (where Protein S is produced) and vitamin K deficiency (as Protein S is a vitamin K-dependent protein). Pregnancy, certain medications like oral contraceptives or chemotherapy, acute infections, nephrotic syndrome, and recent surgery can also temporarily lower Protein S levels.
Protein S Deficiency from Genetic Inheritance
In contrast to acquired forms, inherited Protein S deficiency is a genetic condition caused by mutations in the PROS1 gene. Individuals with this type are born with a predisposition to lower Protein S levels or impaired Protein S function. This genetic basis means the condition is typically lifelong.
Inherited deficiency often follows an autosomal dominant pattern, meaning only one copy of the altered gene from a parent is needed to be affected. While Protein S levels can fluctuate, the underlying genetic cause remains present. In rare cases, inheriting two altered copies of the gene can result in a severe form of the deficiency, manifesting shortly after birth.
Living with Protein S Deficiency
Managing Protein S deficiency involves strategies to reduce blood clot risk. For individuals who have experienced a blood clot, anticoagulation therapy (blood thinners) is a common approach. Medications such as heparin, warfarin, or direct oral anticoagulants (DOACs) may be prescribed to prevent further clotting. Therapy duration varies, from several months to lifelong, depending on individual circumstances and clot severity.
Even for those without a history of clots, ongoing medical monitoring is important. Healthcare providers may advise avoiding certain medications, such as oral contraceptives, which increase clotting risk. During high-risk situations like surgery, immobility, or pregnancy, prophylactic anticoagulation might be recommended to prevent clot formation. Regular follow-ups with a healthcare professional help tailor management plans, focusing on personalized risk assessment and prevention.