Vitamin K-dependent protein S (PROS1 or protein S) is an essential anticoagulant and multifunctional protein. It serves as a cofactor to activate protein C (APC) in the proteolytic inactivation of potent coagulation factors (F) Va and VIIIa [].Mutations in the PROS1 gene cause THPH5 (thrombophilia due to protein S deficiency, autosomal dominant), a hemostatic disorder characterised by impaired regulation of blood coagulation and a tendency to recurrent venous thrombosis [, ].
