Abstract

Protein S deficiency is a disorder associated with increased risk of venous thrombosis. Protein S, a vitamin K-dependent physiological anticoagulant, acts as a nonenzymatic cofactor to activate protein C in the degradation of factor Va and factor VIIIa. Decreased (antigen) levels or impaired function of protein S leads to decreased degradation of factor Va and factor VIIIa and an increased propensity to venous thrombosis. Protein S circulates in human plasma in two forms: approximately 60 percent is bound to complement component C4b β-chain while the remaining 40 percent is free, only free protein S has activated protein C cofactor activity

Cause

In terms of the cause of protein S deficiency it can be in "inherited" via autosomal dominance.A mutation in the PROS1 gene triggers the condition. The cytogenetic location of the gene in question is chromosome 3, specifically 3q11.1 Protein S deficiency can also be "acquired" due to vitamin K deficiency, treatment with warfarin, liver disease, and acute thrombosis (antiphospholipid antibodies may also be a cause as well)

Pathophysiology

In regards to the mechanism of protein S deficiency, Protein S is principally made in liver cells. Protein S is a cofactor of APC both work to degrade factor V and factor VIII. It has been suggested that Zn2+ might be necessary for Protein S binding to factor Xa.

Mutations in this condition change amino acids, which in turn disrupts blood clotting. Functional protein S is lacking, which normally "turns off" clotting proteins, this increases risk of blood clots.

Diagnosis

The diagnosis for deficiency of protein S can be done via reviewing family history of condition and genetic testing, as well as the following:

- Protein S antigen test

- Coagulation test (prothrombin time test)

- Thrombotic disease investigation

- Factor V Leiden test

Diagnosis | Differential diagnosis

Among the possibilities for differential diagnosis of protein S deficiency are- Antiphospholipid syndrome, disseminated intravascular coagulation and antithrombin deficiency (though this list is not exhaustive)

Diagnosis | Types

There are three types of hereditary protein S deficiency:

- Type I – decreased protein S activity: decreased "total" protein S levels, as well as decreased free protein S levels

- Type II – decreased in regards to the "cofactor" activity of the protein

- Type III – decreased protein S activity: decreased free protein S levels (normal total protein S levels)

Treatment

In terms of treatment for protein S deficiency the following are consistent with the "management" (and administration of) individuals with this condition ( it should be noted that the prognosis for "inherited" homozygotes is usually in line with a higher incidence of thrombosis for the affected individual):