Objective—The relative balance between clot formation and fibrinolysis is considered to reflect thrombotic potential following vascular injury (1) to determine the contribution of genetic and environmental factors to variance in measures of clot structure/function in the Leeds Family Study, and (2) to determine the relationship between measures of clot structure/function and cardiovascular risk.

Methods and Results—Using high throughput turbidimetric assays, heritabilities of measures of clot formation, clot structure, and clot lysis were 0.30. Fibrinogen contributed to variance in all measures and plasminogen activator inhibitor-1 to variance in lysis variables. Subjects at increased cardiovascular risk attributable to the presence of the metabolic syndrome (MetS) had increased clot density (MaxAbs_C: 0.358 [0.340, 0.375]au) and prolonged lysis times (Lys_T: 510 [4884, 5328]s) compared with those without MetS (MaxAbs_C: 0.319 [0.310, 0.328]au, P=0.003; Lys_T: 7221 [6569, 7939]s, P<0.001). Furthermore, measures of clot structure/function increased progressively with increasing number of MetS components.

Conclusions—This study indicates that genetic factors contribute modestly to variance in clot structure/function and that clot structure/function is related to presence of the MetS and number of MetS components. Identification of the genetic and environmental factors influencing clot structure/function may further our understanding of the underlying factors predisposing to cardiovascular disease.