Clustering of hypertension, diabetes, and obesity in adult male twins: same genes or same environments?

We investigated the mediating role of genetic factors in the clustering of hypertension, diabetes, and obesity, using the twin registry maintained by the National Academy of Sciences--National Research Council. The study sample included 2,508 male twin pairs born between 1917 and 1927 who responded to a mailed questionnaire that covered demographic variables, cardiovascular risk factors, and health behaviors. The incidence of hypertension and diabetes in this cohort was ascertained from subjects' self-report of a physician diagnosis and/or the use of prescription medications. The body-mass index calculated from self-reports of height and weight was used as a measure of obesity. Descriptive analyses indicated probandwise concordance rates of 34.0%, 31.2%, and 32.7%, respectively, for the joint occurrences of hypertension and diabetes, hypertension and obesity, and diabetes and obesity in MZ twin pairs. Corresponding concordance rates in DZ twin pairs were 8.1%, 14.9%, and 2.8%. The probandwise concordance for the clustering of all three conditions in the same individuals was 31.6% in MZ pairs and 6.3% in DZ pairs (relative risk 5.0; X2(1) = 2.6; P < .15). Multivariate genetic modeling of the correlation in liabilities to develop these conditions suggested the presence of a common latent factor mediating the clustering of hypertension, diabetes, and obesity in this twin sample. This common factor was influenced by both genetic and environmental effects (59% 8 genetic, 41% environmental). The genetic influences on the common latent factor were due to dominant rather than additive sources; the environmental influences appeared to be specific rather than shared by co-twins.