Summary

Differences in genetic influence on death from CHD betweenmales and females have been reported. Haemostatic factorshave consistently been associated with risk for coronary heartdisease (CHD), but sex differences in genetic architecture havenot been studied. This study in middle-aged twins investigateswhether there are sex differences in means and in genetic and/or environmental variance components of haemostatic risk factorsfor CHD. A total of 93 monozygotic twin pairs (44 male and49 female) and 116 dizygotic twin pairs (36 male, 40 female and40 opposite sex) were available for this study. Structuralequation modelling was used to estimate the relative influenceof genetic and environmental factors on variation in levels of fibrinogen, tissue plasminogen activator (tPA) antigen and vonWillebrand factor (vWF). Mean levels of tPA and vWF increasedwith age. Oral contraceptive pill (OCP) and menopause had significantinfluences on levels of fibrinogen and tPA. Genetic influencesexplained 39, 66 and 72% of the variation in levels of fibrinogen,tPA and vWF, respectively. No quantitative or qualitativedifferences of genetic influences on haemostatic levelswere seen between males and females. Haemostatic factors mayaccount for a significant part of the genetic risk for cardiovasculardisease. No difference in genetic architecture for levels of fibrinogen,tPA or vWF was observed between males and females.