SummaryDifferencesi ng enetic influence on deathf romC HD between males and females have been reported. Haemostatic factors have consistentlybeen associated with riskf or coronaryheart disease (CHD), butsex differencesingenetic architecturehave not been studied.This study in middle-agedt wins investigates whetherthere aresex differencesinmeans and in genetic and/ or environmental variance components of haemostatic riskfactors forCHD.Atotal of 93 monozygotic twin pairs (44 maleand 49 female) and 116dizygotic twin pairs(36 male, 40 femaleand 40 opposite sex) were availablef or this study.S tructural equationmodellingwas usedtoestimatethe relativeinfluence of genetic and environmental factors on variation in levels of fi-
KeywordsTw ins, haemostasis,heritability, sexdifferences, oralcontraceptivepill brinogen,t issuep lasminogen activator (tPA)a ntigen and von Willebrand factor (vWF). MeanlevelsoftPA and vWFincreased with age.Oral contraceptivepill (OCP) andmenopause had significanti nfluenceso nl evelso ff ibrinogen and tPA. Genetic influencesexplained 39, 66 and 72% of the variation in levels of fibrinogen,tPA and vWF, respectively. No quantitativeo rq ualitatived ifferenceso fg enetic influenceso nh aemostatic levels were seen between males and females.Haemostatic factors may account forasignificant partofthe genetic risk forcardiovascular disease.Nodifference in genetic architecturefor levels of fibrinogen,t PA or vWFw as observed between males and females.