Protein S activity

General Information

Protein S is a vitamin K-dependent glycoprotein present in platelets and synthesized by liver and endothelial cells.

Protein S acts as a natural anticoagulant. It is a cofactor of -activated protein C (APC), which ensures the inactivation of coagulation factors Vα and VIIIα. In addition, protein S has anticoagulant activity independent of activated protein C, which prevents the formation of prothrombin complexes.

Congenital protein S deficiency is an autosomal dominant disorder. It occurs in 2-6% of patients with deep vein thrombosis. In these patients, the risk of spontaneous abortion, pregnancy complications and arterial thrombosis is much higher.

Three variants of protein S deficiency have been described: according to total and free protein S antigen levels and plasma protein S activity. Variants I and III are more typical than II - dysfunctional protein S deficiency.

Homozygous protein S deficiency is rare, may present with disseminated intravascular coagulation in infants, and is characterized by complete absence of protein S.

The exact causes of acquired protein S deficiency are unknown. It can develop in the background of any risk factor for thrombosis and occurs more often than congenital forms. Acquired protein S deficiency may be due to: vitamin K deficiency, anticoagulation therapy, liver disease, thrombotic thrombocytopenic purpura, pregnancy, estrogen therapy, nephritic syndrome, sickle cell anemia, and others.