Hypertension prevalence is much higher in African-Americans (AAs) than in European-Americans (EAs). It is unknown whether this difference is related to potential ethnic differences in the relative contribution of genes and environment to population variation in blood pressure and underlying hemodynamics. We studied 308 EA and 226 AA twin pairs, including monozygotic and dizygotic twins, of the same as well as the opposite sex (meanϮSD age, 14.7Ϯ3.1 years). Supine resting systolic blood pressure

more »

... (SBP), diastolic blood pressure (DBP), pulse pressure, and heart rate (HR) were measured by a Dinamap instrument and hemodynamics (stroke volume, cardiac index, and total peripheral resistance [TPR] index) by impedance cardiography. Ethnic and sex effects on genetic and environmental contributions to resting blood pressure and hemodynamics were estimated by genetic model fitting. For most measures, the best-fitting model showed no differences in heritability between AAs and EAs or between males and females, with heritabilities of 0.50 for cardiac index, of 0.64 for HR, and of SBP, pulse pressure, and stroke volume in between. Heritability of DBP was 0.45 in EAs and 0.58 in AAs with no effect of sex. For TPR index in EAs, 46% of the variance could be attributed to familial effects, but no significant distinction could be made between shared environmental and genetic factors. Heritability of TPR index in AAs was 0.51. Adjustment for obesity yielded virtually identical heritabilities. In summary, relative influences of genetic and environmental factors on blood pressure and hemodynamics in AA and EA youth are similar and independent of (genes for) obesity. (Hypertension. 2003;41:1196-1201.)