Blood pressure in blacks: Twin studies in barbados

Abstract

We have recently reported that there are significant genetic influences on the population variation in blood pressure in black twins in Los Angeles. The present cross-sectional study was undertaken to replicate these findings in a black twin population that lives in a different biosocial environment We chose the Caribbean island nation of Barbados, where 96% of the population is black, the literacy rate is 99%, and the access to health care Is guaranteed. The goals were 1) to test the feasibility of twin studies in blood pressure research in a developing country and 2) to estimate the relative contribution of genes and environment to blood pressure variability in blacks in the Caribbean. The names of 200 twin sets were obtained with the assistance of community resources including a twin dub, by media advertisement, and by asking people at public blood pressure screenings if they knew any twins. By using these methods, we identified 200 sets of twins. Of these, 37.5% (75/200) met our criteria for study. Although 97% of the sets of twins (73/75) said they were willing to participate, only 69% (52/75) were able to be scheduled during the 1 week of the study when the hill team of investigators was in Barbados. Of those scheduled, 83% (43/52) were examined. Examination included medical history, physical examination, recumbent blood pressure measurements by two observers, anthropometric measurements, 24-hour urine collections for sodium and potassium tests, and blood tests for zygosity. Zygosity was determined by history, multiple genotyping, or both, which classified 21 pairs as monozygotic (13 male and eight female) and 22 pairs as dizygotic (11 female and 11 male). The average age was 29±9.5 (±SD) years, average height was 169±9.2 cm, average weight was 69±3.8 kg, average triceps skin-fold thickness was 11.3±6J> mm, average arm circumference was 29±3.9 mm, average systolic blood pressure was 118 ±10.3 mm Hg, average sodium excretion was 131±65J mM/24 hours, and average potassium excretion was 46± 17 mM/24 hours. In male twins, the quantifiable traits such as height, weight, triceps skin-fold thickness, arm circumference, and systolic blood pressure were all under significant genetic influence. The intradass correlation for systolic blood pressure in all twin pairs was 0.67 (p<0.001), strong evidence for family aggregation of blood pressure. Twin analysis suggested that the mqjor source of variance for systolic blood pressure between individuals was genetic, and heritability in males was estimated to be 70%. The heritability of blood pressure was not explained by any of the other measured variables. Within-twin-pair comparisons did not suggest that the twin with the highest blood pressure was taller, heavier, or consumed more sodium or less potassium. The twin with the thickest triceps skin folds, however, had a higher blood pressure. These results suggest that in blacks in the Caribbean, as in the United States, the major source of variation in blood pressure in the population Is Inherited factors and that twin studies are feasible in developing countries. © 1990 American Heart Association, Inc.