Proteins C and S deficiency

Vitamin K dependent factors. Protein S is a cofactor for anticoagulant activity of activated protein C (APC). APC cleaves factors V and VIII on phospholipid surfaces thus limiting thrombin generation. Deficiency results in prothrombotic state and increased risk of VTE.

Less common than FVL, they account for 4-8% of familial thrombosis. Concentrations are low in early life (up to 4 years for PC), following recent thrombosis, vitamin K deficiency, warfarin therapy, in pregnancy (PS) so care must be taken before diagnosing an inherited deficiency. 397 DNA techniques available but not practical for routine diagnosis.

Many patients are asymptomatic and will never have a VTE. Clinically PC and PS deficiency are similar—spontaneous and sometimes recurrent thrombophlebitis and VTE. In neonates with severe deficiency (homozygous) purpura fulminans is life threatening. This is due to microvascular thrombosis (DIC). Skin necrosis may complicate warfarin therapy.

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