Genetic, Familial and Racial Influences on Blood Pressure Control Systems in Man

This paper reviews investigations by the Indiana University Medical Centre Hypertension Research Centre into genetic influences on blood pressure control systems in man. Our studies have used the families of adult identical twins to partition the relationships of age, sex and body size to the genetic contribution to blood pressure variability. These studies provide little evidence for environmental influence on the familial aggregation of blood pressure and suggest that at least 63% of the variability is due to genetic factors. Studies on the renin-angiotensin-aldosterone system and on the kidney's ability to excrete sodium were also undertaken in identical and fraternal twins, as well as in black and white subjects, and provided unequivocal evidence of genetic control. Studies in first degree relatives of patients with essential hypertension have demonstrated higher plasma renin levels and a decreased ability to excrete a sodium load when compared to first degree relatives of normotensive subjects. Blacks in the U.S.A. have a decreased ability to excrete a sodium load and a greater rise in blood pressure with sodium loading than do whites. We suggest that the heritability of blood pressure is directly related to a genetic influence on the level of renin and that this increase in renin level results in subtle increases in angiotensin II. These chronic elevations of angiotensin II directly increase blood pressure and decrease the kidney's ability to excrete sodium by either a direct renal effect or indirectly by stimulating aldosterone-dependent sodium retention.