Protein S deficiency may be expected in ≈1 of every 500 people 3.
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.
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