With the aim of establishing whether the HR2 haplotype in factor V affects the risk of venous thromboembolism, a retrospective multicenter cohort study was performed in 810 family members identified through 174 probands who suffered from at least 1 episode of deep vein thrombosis and/or pulmonary embolism and had an inherited defect associated with thrombophilia (antithrombin, protein C, or protein S deficiency; factor V R506Q or prothrombin G20210A).
We chose to evaluate whether or not a state of biochemical hypercoagulability was present in 74 individuals (69 heterozygotes and 5 homozygotes) resistant to activated protein C (APC) due to the Arg506 --> Gln mutation in the factor V gene.