PB0955 - The prothrombin mutations associated thrombophilia

Background: Prothrombin plays important roles in both pro- and anti- coagulation reactions, and specific heterozygous missense mutations had been shown to contribute to thromboembolic diseases.

Aims: To explore the prevalence of prothrombin mutations in a cohort of patients with venous thromboembolism (VTE) and to clarify common pathogenetic mechanisms of heterozygous prothrombin mutation related VTE.

Methods: A cohort of 347 patients who had unprovoked VTE under 50 years old were enrolled, except that a positive family history was presented, and screened by a thrombophilia genetic panel containing 35 genes involved in thrombosis and hemostasis. This study was approved by the ethics committee of Ruijin Hospital and informed consent was obtained from each investigated individual. Thrombin generation tests were applied to evaluate the hypercoagulation states of different prothrombin mutation carriers. The impact of novel thrombotic mutations on functions of prothrombin and homeostasis of coagulation activities were also evaluated with recombinant prothrombin mutants.

Results: Heterozygous prothrombin mutations were identified in 3.5% patients (12/347), including Phe382Ser (c.1145T>C), Phe382Leu (c.1146C>A), Arg541Trp (c.1621C>T), Arg596Gln (c.1787G>A) and Asp597Tyr (c.1789G>T). Family investigation identified 30 mutations carriers from the twelve pedigrees, of which eight had positive family history and totally 50% (15/30) mutation carriers had experienced thrombotic events. Procoagulant activities of mutation carriers was moderately reduced but antigen levels were normal, showing an activity to antigen ratio around 0.6-0.8. Thrombin generation tests suggested a hypercoagulable state in plasma samples of the five mutation carriers in the presence of soluble thrombomodulin. Arg541Trp, Arg596Gln and Asp597Tyr showed varying degrees of resistance to antithrombin inhibition and impairment of PC activation ability. Phe382 related mutations exhibited reduced PC activation causing by decreased binding between thrombin and thrombomodulin.

Conclusion(s): The heterozygous prothrombin missense mutations conferring antithrombin resistance and/or impaired PC pathway activity constitute an important risk factor for VTE.