Protein S deficiency - Definition and Overview

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).

External links

• OMIM 176880 (http://www.ncbi.nlm.nih.gov/entrez/dispomim.cgi?id=176880)
• Protein S Deficiency And Thrombophilia (http://www.protein.org.uk/)