Factor VII
Factor VII (old name proconvertin) is one of the central proteins in the coagulation cascade. It is an enzyme (EC 3.4.21.21) of the serine protease class.
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Physiology
The main role of factor VII (FVII) is to initiate the process of coagulation in conjunction with tissue factor (TF). Tissue factor is found on the outside of blood vessels - normally not exposed to the bloodstream. Upon vessel injury, tissue factor is exposed to the blood and circulating factor VII. Once bound to TF, FVII is activated to FVIIa by different proteases, among which are thrombin (factor IIa), activated factor X and the FVIIa-TF complex itself. The most important substrates for FVIIa-TF are Factor X and Factor IX.
The action of the factor is impeded by tissue factor pathway inhibitor (TFPI), which is released almost immediately after initiation of coagulation. Factor VII is vitamin K dependent; it is produced in the liver. Use of warfarin or similar anticoagulants impairs its function.
Genetics
The gene for factor VII is located on chromosome 13 (13q34).
Role in disease
Deficiency is rare (congenital proconvertin deficiency) and inherits recessively.
Therapeutic use
Recombinant human factor VIIa (NovoSeven®, ATC code B02BD05) has been introduced for use in uncontrollable bleeding in hemophilia patients who have developed inhibitors against replacement coagulation factor.
It is being increasingly used in uncontrollable hemorrhage. The rationale for its use in hemorrhage is, that it will only induce coagulation in those sites where tissue factor (TF) is also present. Indeed, there is no report on significantly increased thrombosis risk in rhFVIIa use.
Reference
- Roberts HR, Monroe DM, White GC. The use of recombinant factor VIIa in the treatment of bleeding disorders. Blood 2004;104:3858-64. PMID 15328151.