Protein S deficiency
Protein S deficiency is a disorder associated with increased risk of thrombosis. more...
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.
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).
Hereditary PSD is an autosomal dominant condition, resulting in a 50 precent chance of passing the disease to offspring. Less than half of those diagnosed with PSD will experience thrombosis, and those who do usually are affected only from the age of the late teens onwards. A positive blood test can lead to the loss of health insurance benefits and/or employment, and the social downsides need to be balanced against the actual medical benefit of accurate diagnosis. Screening of young children is usually deferred because early testing is often inaccurate, and it is better to wait until they are old enough to decide for themselves whether they want to be tested.
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