Protein S deficiency is a disorder associated with increased risk of venous thrombosis.[1]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.[3]
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. Some risk factors for deep vein thrombosis or pulmonary embolism in patients with protein S deficiency include pregnancy, older age, hormonal therapy, consumption of birth control pills, recent surgery, trauma, and physical inactivity.[4] 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[medical citation needed]
Signs and symptoms
Among the possible presentation of protein S deficiency are:[1][2][5][4]
In regards to the mechanism of protein S deficiency, Protein S is made in liver cells and the Endothelium.[8][9] 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.[2][10]
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.[6]
Diagnosis
PTT blood tests Vacutainer tube
The diagnosis for deficiency of protein S can be done as part of a thrombophilia investigation, along with reviewing family history of thrombotic disease.[1][11][12] Testing for protein S deficiency should be delayed if there are causes for acquired deficiency or interfering factors.[13]
The initial assay for congenital protein S deficiency should be the free protein S antigen assay. If the level is low, total protein S antigen assay can be performed to differentiate between type I and type III deficiency. Protein S activity assays may be useful in patients with a normal free protein S antigen in occasional situations: 1) if no abnormality is identified during a thrombophilia workup, but clinical suspicion persists; or 2) in specific populations in which
type II deficiencies are more common.[13]
Screening with a free protein S antigen assay is preferred because there are fewer interferences compared to assays for protein S activity, as well as better assay performance characteristics.[13]
There are three types of hereditary protein S deficiency:[2][6]
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
Dabigatran etexilate
In terms of treatment for protein S deficiency the following are consistent with the management (and administration of) individuals with this condition (the prognosis for inheritedhomozygotes is usually in line with a higher incidence of thrombosis for the affected individual[1]):[2][10]
^ abcMarlar RA, Gausman JN, Tsuda H, Rollins-Raval MA, Brinkman HJM. Recommendations for clinical laboratory testing for protein S deficiency: Communication from the SSC committee plasma coagulation inhibitors of the ISTH. J Thromb Haemost. 2021 Jan;19(1):68-74. doi: 10.1111/jth.15109. PMID 33405382.
Further reading
ten Kate M, Mulder R, Platteel M, Brouwer J, van der Steege G, van der Meer J (2006). "Identification of a novel PROS1 c.1113T→GG frameshift mutation in a family with mixed type I/type III protein S deficiency". Haematologica. 91 (8): 1151–2. PMID16885060.
Wypasek, Ewa; Undas, Anetta (1 August 2016). "Protein C and protein S deficiency - practical diagnostic issues". Advances in Clinical and Experimental Medicine. 22 (4): 459–467. ISSN1899-5276. PMID23986205.
