High Heritability of Ambulatory Blood Pressure in Families of East African Descent

Abstract

Abstract-We estimated the heritability of ambulatory systolic blood pressure (SBP), diastolic blood pressure (DBP), and pulse pressure (PP) in east African families with at least 2 hypertensive siblings and living in the Seychelles islands (Indian Ocean). The sample consisted of 314 individuals (147 men and 167 women), both normotensive and hypertensive, from 76 pedigrees (meanϮSD of 4.1Ϯ2.8 persons per pedigree). After a 2-week off-treatment period, daytime and nighttime ambulatory blood pressure (BP) was monitored. Office BP was measured with a standard mercury sphygmomanometer. We estimated by maximum likelihood the age-and sex-adjusted heritabilities from the additive polygenic component of the variance of the traits allowing for the presence of other familial correlations. We also adjusted for ascertainment (ie, for the fact that 2 siblings had to be hypertensive) and examined the effect of adjusting for body mass index, 24-hour urinary excretion of sodium and potassium, plasma renin activity, and plasma aldosterone concentration. Heritability estimates (ϮSE) for ambulatory SBP, DBP, and PP were, respectively, 0.37Ϯ0.12/0.24Ϯ0.12/0.54Ϯ0.12 for daytime and 0.34Ϯ0. Key Words: blood pressure monitoring, ambulatory Ⅲ genetics Ⅲ ethnicity Ⅲ blacks H ypertension, which affects approximately one-third of the adult population in Western countries, 1 is now becoming a substantial burden in African countries as well, with prevalence ranging from 16% to 32% among adults. [2][3][4][5] Because individuals of African descent are more prone to hypertension-related complications than whites, 6 -8 a better understanding of the familial aggregation of blood pressure (BP) in this ethnic group is of particular importance for unraveling the genetic variants influencing BP.Heritability is a measure of familial aggregation caused by genetic factors. Narrow sense heritability is the proportion of the total phenotypic variance that is caused by the additive genetic variance (ie, that part of the genetic variance caused by the average effects of individual alleles, which reflects transmissible resemblance between relatives). A high heritability identifies good candidate phenotypes for further genetic studies. Studies conducted so far in Africa 9 -11 used conventional BP measurement and found heritability estimates ranging from 0.34 to 0.45 for systolic BP (SBP) and from 0.29 to 0.43 for diastolic BP (DBP).Two studies have measured the heritability of ambulatory BP in nontwins 12 . 13 Daytime heritability estimates for SBP/ DBP were 0.32/0.25 in a study of black affected sibpairs 12 and 0.33/0.22 in a study of Swedish families. 13 Nighttime heritability estimates for SBP/DBP were 0.69/0.51 in the former 12 and 0.37/0.32 in the latter. 13 To date, only the Swedish study 13 has reported the heritability of ambulatory pulse pressure (PP) (0.53/0.34 for daytime/nighttime).We estimated the heritability of ambulatory SBP, DBP, and PP in families of African descent with at least 2 hypertensive siblings and living in the Seychelles islands (...

Genetic influence on blood pressure measured in the office, under laboratory stress and during real life

“…Second, it was not tested whether the increase in 24-h BP heritability was statistically significant in these two studies. According to the study by Bochud et al ., 30 which provided the standard error of the estimated heritabilities, we found a large overlap between the 95%confidence interval of 24-h and office SBP heritabilities, which indicates that the increase in 24-h SBP heritability does not reach statistical significance. Third, an increase in heritability does not necessarily mean an increase in statistical power to find genes, because 24-h and office BP may be influenced by partly different genes.…”

“…To date, four twin studies 25–28 and three family studies 29–31 have reported heritability estimates for 24-h ABP recording. However, only three studies 25,30,31 reported the heritability estimates both for office and 24-h BP, with two family studies 30,31 observing higher heritability and one twin study observing similar heritability for 24-h BP. 25 For example, in the study by Fava et al ., 31 which included 260 siblings from 118 Swedish families, the heritability was 30% for 24-h SBP and 29% for 24-h DBP, whereas the heritability estimates for office BP were not significantly different from zero.…”

“…25 For example, in the study by Fava et al ., 31 which included 260 siblings from 118 Swedish families, the heritability was 30% for 24-h SBP and 29% for 24-h DBP, whereas the heritability estimates for office BP were not significantly different from zero. In the study by Bochud et al ., 30 which included 314 subjects from 76 AA pedigrees, the heritability was 40% for 24-h SBP and 28% for 24-h DBP, whereas it was only 20% for office SBP and 5% for office DBP. In the study by Fagard et al ., 25 which included 26MZ and 27 DZ pairs, the heritability was 70% for 24-h SBP and 73% for 24-h DBP, which was similar to the results for the office BP (64 and 73%, respectively).…”

“…However, there are three caveats. First, these two family studies 30,31 might be underpowered to detect the heritability of office BP. Previous family and twin studies have established that office BP is heritable, 1 whereas both of these two studies failed to detect a significant heritability for office BP.…”

Heritability of Ambulatory and Beat-to-Beat Office Blood Pressure in Large Multigenerational Arab Pedigrees: The ‘Oman Family Study’

“…The consequent rapid population growth produced young isolates of 7-12 generations each. A more detailed description of the cohort stratification and the OFS design can be found in earlier reports (Bochud et al, 2005). Hypertension was diagnosed when subjects had a 24-hour SBP and/or DBP ≥135/85 mmHg (Pickering et al, 2005) or when they were on antihypertensive treatment.…”