Protein S deficiency is a disorder associated with increased risk of thrombosis. Decreased levels or impaired function of protein S, a vitamin K-dependant physiological anticoagulant leads to decreased degradation of factor Va and factor VIIIa and an increased propensity to venous thrombosis.
Types
There are three types of hereditary protein S deficiency:
- Type I - decreased protein S activity: low levels of free protein S, normal levels of bound protein S
- Type IIa - decreased protein S activity: low levels of free protein S, low levels of bound protein S
- Type IIb - decreased protein S activity: normal levels of free protein S, normal levels of bound protein S
Decreased activity is present in an acquired form in vitamin K deficiency or treatment with warfarin. This generally also impairs the coagulation system itself (factors II, VII, IX and X), and therefore predisposes to bleeding rather than thrombosis. Protein S levels are also lower in pregnancy and liver disease.
Protein S deficiency is the underlying cause of a small proportion of cases of disseminated intravascular coagulation (DIC), deep venous thrombosis (DVT) and pulmonary embolism (PE).
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