GENETIC SUSCEPTIBILITY TO DEATH FROM CORONARY HEART-DISEASE IN A STUDY OF TWINS

Background. A family history of premature coronary heart disease has l ong been thought to be a risk factor for coronary heart disease. Using data from 26 years of follow-up of 21,004 Swedish twins born between 1886 and 1925, we investigated this issue further by assessing the ris k of death from coronary heart disease in pairs of monozygotic and diz ygotic twins. Methods. The study population consisted of 3298 monozygo tic and 5964 dizygotic male twins and 4012 monozygotic and 7730 dizygo tic female twins. The age at which one twin died of coronary heart dis ease was used as the primary independent variable to predict the risk of death from coronary heart disease in the other twin. Information ab out other risk factors was obtained from questionnaires administered i n 1961 and 1963. Actuarial life-table analysis was used to estimate th e cumulative probability of death from coronary heart disease. Relativ e-hazard estimates were obtained from a multivariate survival analysis . Results. Among the men, the relative hazard of death from coronary h eart disease when one's twin died of coronary heart disease before the age of 55 years, as compared with the hazard when one's twin did not die before 55, was 8.1 (95 percent confidence interval, 2.7 to 24.5) f or monozygotic twins and 3.8 (1.4 to 10.5) for dizygotic twins. Among the women, when one's twin died of coronary heart disease before the a ge of 65 years, the relative hazard was 15.0 (95 percent confidence in terval, 7.1 to 31.9) for monozygotic twins and 2.6 (1.0 to 7.1) for di zygotic twins. Among both the men and the women, whether monozygotic o r dizygotic twins, the magnitude of the relative hazard decreased as t he age at which one's twin died of coronary heart disease increased. T he ratio of the relative-hazard estimate for the monozygotic twins to the estimate for the dizygotic twins approached 1 with increasing age. These relative hazards were little influenced by other risk factors f or coronary heart disease. Conclusions. Our findings suggest that at y ounger ages, death from coronary heart disease is influenced by geneti c factors in both women and men. The results also imply that the genet ic effect decreases at older ages.