Rühl H, et al. - An extremely variable clinical phenotype is exhibited by carriers of the most common prothrombotic mutations factor V Leiden (FVL) and prothrombin (FII) 20210G>A, and that acceleration of thrombin and activated protein C (APC) formation due to FVL mutation in carriers without a history of venous thromboembolism (VTE) has recently been reported, researchers assessed if a comparable reaction pattern is caused by the FII 20210G>A mutation, and if the response rates vary in FVL and FII 20210G>A mutation carriers with prior VTE. For this prospective cohort investigation, 30 FVL carriers, 28 FII 20210G>A carriers, and 15 healthy controls were assessed. By in vivo data, an intermediate phenotype with increased thrombin formation following coagulation activation was shared by the FII 20210G>A and FVL mutations. The APC activating capacity of FVL carriers was found to alter the thrombotic risk of this common prothrombotic mutation.