Fifteen percent of myocardial infarctions and coronary revascularizations explained by family history unrelated to conventional risk factors. The Reykjavik Cohort Study

Aims To examine the relationship between history of myocardial infarction in first-degree relatives and the risk of developing coronary heart disease (myocardial infarction or coronary revascularization). Methods and Results A total of 9328 males and 10062 females, randomly selected residents of the Reykjavik area, aged 33-81 years, were examined in the period from 1967 to 1996 in a prospective cohort study. Cardiovascular risk assessment was based on characteristics at baseline. Information on history of myocardial infarction in first-degree relatives was obtained from a health questionnaire. Mean follow-up was 18 and 19 years for men and women, respectively. During follow-up 2700 men and 1070 women developed coronary heart disease. Compared with subjects without a family history, the hazard ratio of coronary heart disease was 1.75 (95% confidence interval, CI, 1.59-1.92) for men and 1.83 (95% CI, 1.60-2.11) for women, with one or more first-degree relatives with myocardial infarction. The risk factor profile was significantly worse in individuals with a positive family history. After allowance for these risk factors, the hazard ratio was still highly significant, 1.66 (CI, 1.51-1.82) and 1.64 (CI, 1.43-1.89) for men and women, respectively. Family history of myocardial infarction was attributed to 15.1% of all cases of coronary heart disease in men and 16.6% in women, independent of other known risk factors. Conclusion Family history of myocardial infarction increases the risk of developing coronary heart disease in both men and women and is largely independent of other classic risk factors. Approximately 15% of all myocardial infarctions can be attributed to familial factors that have not been measured in the study or remain to be elucidated.