Activation Markers of Coagulation and Fibrinolysis in Twins: Heritability of the Prethrombotic State

Background: Activation markers of coagulation and fibrinolysis are increased in individuals at risk of coronary-artery disease and other thrombotic disorders--a condition defined as the prethrombotic state. We aimed to find out the extent to which the prethrombotic state is determined by genetic factors.

Methods: We analysed concentrations of prothrombin, prothrombin fragment 1+2, thrombin-antithrombin complex, crosslinked fibrin degradation product D-dimer, and thrombin-activatable fibrinolysis inhibitor by ELISA in 118 monozygotic and 112 dizygotic unselected female twins aged 21-73 years from the St Thomas' UK Adult Twin Registry. We used quantitative genetic-model fitting to estimate heritability.

Findings: We found significant heritabilities in concentrations of the activation markers in plasma. Genetic factors contributed 45, 40, and 65% of the variation in concentrations of fragment 1+2, thrombin-antithrombin complex, and D-dimer, respectively. Age was important only in fragment 1+2 concentrations, in which it accounted for 12% of the variation. The remaining variation could be attributed to unique environmental factors. Variation in concentrations of precursor prothrombin in plasma was determined by 57% heritability, and that of zymogen thrombin-activatable fibrinolysis inhibitor showed a very strong genetic component (82%).

Interpretation: The activation mechanisms of the coagulation and fibrinolytic systems, and therefore the prethrombotic state, are controlled to a substantial degree by genetic factors. Genes influencing activation of haemostasis are likely to be an important component of the overall thrombotic tendency in the general population.