Heritability of renal function in hypertensive families of African descent in the Seychelles (Indian Ocean)

Influence of Genomic Loci on Measures of Chronic Kidney Disease in Hypertensive Sibships

Genomewide linkage analyses were conducted of serum creatinine, estimated GFR (eGFR), and urine albumin-creatinine ratio (UACR) in search of genetic susceptibility loci for chronic kidney disease in 1351 black (median age 63 yr, 70% women, 79% hypertensive) and 1022 white individuals (median age 61 yr, 56% women, 75% hypertensive) from sibships in which two or more members had essential hypertension diagnosed before age 60 yr. After adjustment for gender, age, diabetes, and use of angiotensin inhibitors, the logarithm-transformed measure of serum creatinine was heritable in both ethnic groups (0.45 in black individuals [P < 0.001]; 0.39 in white individuals [P < 0.001]), as was eGFR (0.52 in black individuals [P < 0.001]; 0.39 in white individuals [P < 0.001]). Log UACR was heritable in black individuals (0.30, P < 0.001) but not in white individuals (0.12; P = 0.059). In black individuals, the univariate maximum multipoint logarithm of odds scores (MLS) were observed on chromosome 7 for log serum creatinine (MLS = 3.65, at 43 cM from pter; P = 0.00002) and eGFR (MLS = 2.52, at 45 cM from pter; P = 0.00033) and for log UACR (MLS = 2.91, at 112 cM from pter; P = 0.00012). In white individuals, only one MLS for log serum creatinine and one for eGFR achieved the logarithm of odds score criterion for "suggestive" evidence of linkage (2 < or = MLS < 3), both on chromosome 3 (at 211 and 209 cM, respectively); however, none did so for log UACR. In black individuals, bivariate linkage analyses of log serum creatinine and pulse pressure (i.e., systolic-diastolic BP) provided "suggestive" evidence of a region on chromosome 5 with pleiotropic effects on both traits (MLS = 3.62, at 85 cM from pter; P = 0.00023). These findings support the utility of genetic linkage analyses for identification of novel risk factors that influence measures of chronic kidney disease, particularly among black individuals.

Association of CYP3A5 genotypes with blood pressure and renal function in African families

OBJECTIVE

Renal cytochrome P450 3A5 (CYP3A5) activity has been associated with blood pressure and salt sensitivity in humans. We determined whether CYP3A5 polymorphisms are associated with ambulatory blood pressure (ABP) and with glomerular filtration rate (GFR) in African families.

METHODS

Using a cross-sectional design, 375 individuals from 72 families, each with at least two hypertensive siblings, were recruited through a hypertension register in the Seychelles (Indian Ocean). We analyzed the association between the CYP3A5 alleles (*1, *3, *6 and *7) and ABP, GFR and renal sodium handling (fractional excretion of lithium), from pedigree data, allowing for other covariates and familial correlations.

RESULTS

CYP3A5*1 carriers increased their daytime systolic and diastolic ABP with age (0.55 and 0.23 mmHg/year) more than non-carriers (0.21 and 0.04 mmHg/year). CYP3A5*1 had a significant main effect on daytime systolic/diastolic ABP [regression coefficient (SE): -29.6 (10.0)/-8.2 (4.1) mmHg, P = 0.003/0.045, respectively] and this effect was modified by age (CYP3A5*1 x age interactions, P = 0.017/0.018). For night-time ABP, the effect of CYP3A5*1 was modified by urinary sodium excretion, not by age. For renal function, CYP3A5*1 carriers had a 7.6(3.8) ml/min lower GFR (P = 0.045) than non-carriers. Proximal sodium reabsorption decreased with age in non-carriers, but not in CYP3A5*1 carriers (P for interaction = 0.02).

CONCLUSIONS

These data demonstrate that CYP3A5 polymorphisms are associated with ambulatory BP, CYP3A5*1 carriers showing a higher age- and sodium- related increase in ABP than non-carriers. The age effect may be due, in part, to the action of CYP3A5 on renal sodium handling.

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

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 (mean±SD of 4.1±2.8 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 (±SE) for ambulatory SBP, DBP, and PP were, respectively, 0.37±0.12/0.24±0.12/0.54±0.12 for daytime and 0.34±0.13/ 0.37±0.15/0.47±0.12 for nighttime measurements ( P <0.05 for all estimates). Heritability estimates for office SBP, DBP, and PP were, respectively, 0.20±0.11, 0.05±0.09, and 0.37±0.12. Heritability estimates for SBP varied markedly according to whether participants were treated for hypertension at baseline. The present data show that ambulatory BP and PP have a high heritability in families of African descent. They also demonstrate that antihypertensive treatment and the number of BP measurements have a major influence on the heritability estimates.