Protein S Deficiency

Protein S deficiency is a disorder that causes abnormal blood clotting. When someone bleeds, the blood begins a complicated series of rapid chemical reactions to stop the bleeding. These chemical reactions involve proteins called blood coagulation factors. Other proteins in the blood, such as protein S, usually regulate these chemical reactions to prevent excessive clotting. When protein S is missing (deficient), clotting may not be regulated normally and affected individuals have an increased risk of forming a blood clot called a thrombosis. Protein S deficiency may be inherited or acquired during a person's lifetime. Inherited protein S deficiency is due to genetic variations in the PROS1 gene and is inherited in an autosomal dominant pattern. Acquired protein S deficiency can occur due to kidney or liver disease, infections, and certain exposures. People at risk to have protein S deficiency are those with an individual or family history of multiple blood clots in the veins. Treatment may include taking medication known as blood thinners to decrease the chance of developing a blood clot.