Increased risk for venous thrombosis in carriers of the prothrombin G-->A20210 gene variant.

BACKGROUND

A mutation in the prothrombin gene (G-->A20210) has been associated with higher plasma prothrombin levels and an increased tendency for venous thrombosis.

OBJECTIVE

To determine whether the prothrombin A20210 allele is independently associated with the occurrence of venous thrombosis.

DESIGN

Case-control study.

SETTING

Two thrombosis centers in southern Italy.

PATIENTS

281 consecutive patients with venous thrombosis confirmed by objective tests and 850 controls.

MEASUREMENTS

Medical history was collected on standardized questionnaires. The presence of prothrombin G-->A2020 and factor V Leiden mutations was determined by polymerase chain reaction. The presence of anticoagulant factors and prothrombin activity was determined by tests of function.

RESULTS

In 150 controls, increased prothrombin activity (P < 0.001) was associated with the prothrombin A20210 allele. This allele was more frequent in patients than in controls (8.01% compared with 2.29%; P < 0.001) and was associated with an increased risk for thrombosis (odds ratio, 3.88 [95% CI, 2.23 to 6.74]). The increased prevalence of this allele was independent of the presence of the factor V Leiden mutation. After adjustment for sex, age, arterial thrombosis, and factor V Leiden mutation, the risk was still significantly elevated (odds ratio, 3.13 [CI, 1.89 to 5.21]). Moreover, the overall prevalence of inherited coagulation abnormalities was significantly higher in patients with thrombosis of the lower extremities than in patients with thrombosis of the upper extremities (odds ratio, 3.77 [CI, 1.10 to 12.93]). Fourteen patients carried both the prothrombin G-->A20210 and factor V Leiden mutations.

CONCLUSIONS

The prothrombin A20210 allele is independently associated with the occurrence of venous thrombosis, particularly in patients with a history of thrombosis of the lower extremities.