Protein S deficiency

Protein S deficiency is a hypercoagulable state associated with increased risk of venous thrombosis (up to 5% of patients with deep venous thrombosis may carry this deficiency).


Protein S deficiency may be expected in ≈1 of every 500 people .

Clinical presentation

The spectrum of severity varies in those with mild (heterozygous) protein S deficiency. About 50% of patients present with symptoms by 55 years old. Common presentations include DVT/PE, DIC (disseminated intravascular coagulation) and thrombi of the viscera .

Severe (homozygous) protein S deficiency usually presents in the puerperium with distinctive purpura fulminans (PF). Most individuals succumb during childhood unless treatment is instituted early .


Protein S, a vitamin K-dependent physiological anticoagulant, acts as a non-enzymatic cofactor to activate protein C in the degradation of factor Va and factor VIIIa. Decreased (antigen) levels or impaired function of protein S leads to decreased degradation of factor Va and factor VIIIa and therefore an increased propensity to venous thrombosis.


Most cases are caused by mutations in the PROS1 gene.