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De Stefano et al report a retrospective study to compare the risk of recurrent spontaneous deep vein thrombosis (DTE) in people with different genotypes for factor V and prothrombin, two factors in the coagulation cascade [De Stefano, V. et al (1999) N Engl J Med 341, 801-806 (Abstract)] (see Hereditary thrombophilia page for references to background information). Patients heterozygous for the factor V Leiden mutation and the prothrombin G20210A mutation had a relative risk of 2.6 for recurrent DTE and 3.7 for spontaneous recurrent DTE compared with either people with neither mutation or people with only the factor V Leiden mutation (spontaneous recurrence means recurrence in the absence of known risk factors such as oral contraceptive use or prolonged immobilisation). De Stefano and colleagues conclude that double heterozygotes are "candidates for lifelong anticoagulation" after a first episode of DTE.

Comment: Public health considerations do not at present support the authors' recommendations. Anticoagulant treatment itself carries significant risks, which are likely to be higher than the absolute risk of mortality from recurrent DTE in double heterozygotes. Genetic testing for all patients suffering from a first episode of spontaneous DTE would be extremely expensive and the information would be unlikely to aid in their management.