Family aggregation of cardiovascular disease mortality: a register-based prospective study of pooled Nordic twin cohorts

Background: Familial factors play an important role in the variation of risk factors of cardiovascular diseases (CVD), but less is known about how they affect the risk of death from CVD. We estimated familial aggregation of CVD mortality for twins offering the maximum level of risk due to genetic and other familial factors. Methods: Altogether, 132 771 twin individuals, including 65 196 complete pairs from Denmark, Finland and Sweden born in 1958 or earlier, participated in this study. During the register-based follow-up, 11 641 deaths occurred from coronary heart disease (CHD), including 6280 deaths from myocardial infarct and 4855 deaths occurred from stroke, with 1092 deaths from ischaemic stroke and 1159 deaths from haemorrhagic stroke. Relative recurrence risk ratios (RRRs) with 95% confidence intervals (95% CIs) for monozygotic and dizygotic twins were calculated. Results: In the analyses pooling men and women, the RRR for monozygotic twins was 1.49 (95% CI 1.40-1.57) for CHD and 1.81 for any stroke (95% CI 1.54-2.09). The highest RRR was found for haemorrhagic stroke (3.53 95% CI 2.01-5.04). For dizygotic twins, the RRRs were generally lower. Conclusions: Family aggregation was found for CHD and haemorrhagic stroke. Clustering of risk factors in families increases the risk of CVD.