Genetic Epidemiology of Venous Thromboembolism

BACKGROUND:

Venous thromboembolism is a major national health problem, with at least 201,000 first lifetime cases per year in the United States. Over 50,000 of these patients die within seven days, and for 20 percent, death is rapid, with insufficient time for medical intervention. Recurrent VTE is frequent and also associated with death as well as chronic impairment due to the venous stasis syndrome. Thus, identification of high-risk patients for targeted VTE prophylaxis or treatment is necessary to improve survival and prevent impairment. While clinical risk factors can identify a population at risk, such risk factors have low predictive value for the individual patient. The high prevalence of the Factor V R506Q (Leiden) and Prothrombin 20210G --> A mutations among VTE patients suggests the hypothesis that additional genetic abnormalities of coagulation (thrombophilia) are associated with a substantial proportion of VTE cases.

DESIGN NARRATIVE:

The study had a case-control design. Using stored DNA samples, the investigators screened for mutations within the candidate genes for Factor V R506Q (Leiden) and Prothrombin 20210G --> A using either dideoxy, bi-directional dideoxy, or restriction endonuclease fingerprinting, and performing population-based case-control and cohort studies using a previously identified 30-year VTE inception cohort.

The specific aims were: 1) to screen genomic DNA from patients with VTE for mutations within (candidate) genes encoding for prothrombin, thrombomodulin, tissue factor pathway inhibitor, tissue factor, factor VII, and factor X, and to determine if the mutation predicted a change in either protein expression or structure; 2) in population-based case-control studies, a) to test the hypothesis that such a mutation was associated with VTE, estimate the strength of the association, and determine the independence of the association after controlling for other environmental risk factors and coagulation abnormalities, including interactions, and b) to test the hypothesis that a mutation was associated with death and autopsy; 3) to estimate the attributable risk for VTE associated with each significant mutation, both individually and for all independently significant mutations collectively while controlling for other environmental risk factors and coagulation abnormalities; and 4) in a population-based retrospective cohort study, to estimate the time-to-VTE recurrence and to test the hypothesis that each significant mutation was an independent predictor of VTE recurrence after controlling for other environmental predictors and coagulation abnormalities, including interactions.