Metabolic abnormalities in obesity can overstimulate the renal epithelial sodium channel (ENaC) and subsequently lead to blood pressure (BP) elevation. Prostasin, a membrane-bound/secretive serine protease, is thought to activate ENaC via the proteolytic cleavage of the channel. Our specific aim was to explore whether there is a relationship between adiposity and urinary prostasin excretion at the population level.
In 271 African-American adolescents, urinary prostasin concentrations were determined by enzyme-linked immunosorbent assay and normalized by urinary creatinine.
Urinary prostasin excretion increased in the over- weight/obese group (n = 110, 38.2 ± 4.0 ng/mg) vs. the normal-weight group (n = 161, 20.7 ± 1.2 ng/mg, P = 0.03). Urinary prostasin excretion was significantly correlated with BMI percentiles (r = 0.14, P = 0.02), waist circumference (r = 0.13, P = 0.05), total body fat mass (r = 0.20, P < 0.01), and percentage body fat (r = 0.23, P < 0.01). Urinary prostasin excretion was also correlated with plasma aldosterone (r = 0.11, P = 0.05) and systolic BP (SBP; r = 0.15, P = 0.02), but the significances disappeared after adjustment of any of the adiposity variables.
Our data for the first time suggest that adiposity plays a role in urinary prostasin excretion, and its associations with aldosterone and BP appear to be modulated by adiposity. Whether urinary prostasin excretion is a biomarker/mechanism underlying obesity-related hypertension deserves further investigations.
The QT interval, an electrocardiographic measure reflecting myocardial repolarization, is a heritable trait. QT prolongation is a risk factor for ventricular arrhythmias and sudden cardiac death (SCD) and could indicate the presence of the potentially lethal Mendelian Long QT Syndrome (LQTS). Using a genome-wide association and replication study in up to 100,000 individuals we identified 35 common variant QT interval loci, that collectively explain ∼8-10% of QT variation and highlight the importance of calcium regulation in myocardial repolarization. Rare variant analysis of 6 novel QT loci in 298 unrelated LQTS probands identified coding variants not found in controls but of uncertain causality and therefore requiring validation. Several newly identified loci encode for proteins that physically interact with other recognized repolarization proteins. Our integration of common variant association, expression and orthogonal protein-protein interaction screens provides new insights into cardiac electrophysiology and identifies novel candidate genes for ventricular arrhythmias, LQTS,and SCD.
genome-wide association study; QT interval; Long QT Syndrome; sudden cardiac death; myocardial repolarization; arrhythmias
Heart rate variability is an important risk factor for cardiovascular disease and all-cause mortality. The acetylcholine pathway plays a key role in explaining heart rate variability in humans. We assessed whether 443 genotyped and imputed common genetic variants in eight key genes (CHAT, SLC18A3, SLC5A7, CHRNB4, CHRNA3, CHRNA, CHRM2 and ACHE) of the acetylcholine pathway were associated with variation in an established measure of heart rate variability reflecting parasympathetic control of the heart rhythm, the root mean square of successive differences (RMSSD) of normal RR intervals. The association was studied in a two stage design in individuals of European descent. First, analyses were performed in a discovery sample of four cohorts (n = 3429, discovery stage). Second, findings were replicated in three independent cohorts (n = 3311, replication stage), and finally the two stages were combined in a meta-analysis (n = 6740). RMSSD data were obtained under resting conditions. After correction for multiple testing, none of the SNPs showed an association with RMSSD. In conclusion, no common genetic variants for heart rate variability were identified in the largest and most comprehensive candidate gene study on the acetylcholine pathway to date. Future gene finding efforts for RMSSD may want to focus on hypothesis free approaches such as the genome-wide association study.
Previous genome-wide association studies (GWAS) have identified a large number of genetic variants for obesity and its related traits, representing a group of potential key genes in the etiology of obesity. Emerging evidence suggests that epigenetics may play an important role in obesity. It has not been explored whether the GWAS-identified loci contribute to obesity through epigenetics (e.g., DNA (deoxyribonucleic acid) methylation) in addition to genetics.
A multi-stage cross-sectional study was designed. We did a literature search and identified 117 genes discovered by GWAS for obesity and its related traits. Then we analyzed whether the methylation levels of these genes were also associated with obesity in two genome-wide methylation panels. We examined an initial panel of seven adolescent obese cases and seven age-matched lean controls, followed by a second panel of 48 adolescent obese cases and 48 age- and gender-matched lean controls. The validated CpG sites were further replicated in two independent replication panels of youth (46 vs. 46 and 230 cases vs. 413 controls, respectively) and a general population of youth, including 703 healthy subjects.
One CpG site in the lymphocyte antigen 86 (LY86) gene, which showed higher methylation in the obese in both the initial (p = .009) and second genome-wide DNA methylation panel (p = .008), was further validated in both replication panels (meta p = .00016). Moreover, in the general population of youth, the methylation levels of this region were significantly correlated with adiposity indices (p ≤.02), insulin resistance (p = .001), and inflammatory markers (p < .001).
By focusing on recent GWAS findings in genome-wide methylation profiles, we identified a solid association between LY86 gene DNA methylation and obesity.
DNA methylation; obesity; GWAS; insulin resistance; inflammation
Skin fluorescence (SF) is a non-invasive marker of AGEs and is associated with the long-term complications of diabetes. SF increases with age and is also greater among individuals with diabetes. A familial correlation of SF suggests that genetics may play a role. We therefore performed parallel genome-wide association studies of SF in two cohorts.
Cohort 1 included 1,082 participants, 35–67 years of age with type 1 diabetes. Cohort 2 included 8,721 participants without diabetes, aged 18–90 years.
rs1495741 was significantly associated with SF in Cohort 1 (p < 6 × 10−10), which is known to tag the NAT2 acetylator phenotype. The fast acetylator genotype was associated with lower SF, explaining up to 15% of the variance. In Cohort 2, the top signal associated with SF (p = 8.3 × 10−42) was rs4921914, also in NAT2, 440 bases upstream of rs1495741 (linkage disequilibrium r2 = 1.0 for rs4921914 with rs1495741). We replicated these results in two additional cohorts, one with and one without type 1 diabetes. Finally, to understand which compounds are contributing to the NAT2–SF signal, we examined 11 compounds assayed from skin biopsies (n = 198): the fast acetylator genotype was associated with lower levels of the AGEs hydroimidazolones of glyoxal (p = 0.017).
We identified a robust association between NAT2 and SF in people with and without diabetes. Our findings provide proof of principle that genetic variation contributes to interindividual SF and that NAT2 acetylation status plays a major role.
Electronic supplementary material
The online version of this article (doi:10.1007/s00125-014-3286-9) contains peer-reviewed but unedited supplementary material, which is available to authorised users.
Acetylation; Genome-wide association study; NAT2; Skin autofluorescence; Skin fluorescence; Skin intrinsic fluorescence
Elevated resting heart rate is associated with greater risk of cardiovascular disease and mortality. In a 2-stage meta-analysis of genome-wide association studies in up to 181,171 individuals, we identified 14 new loci associated with heart rate and confirmed associations with all 7 previously established loci. Experimental downregulation of gene expression in Drosophila melanogaster and Danio rerio identified 20 genes at 11 loci that are relevant for heart rate regulation and highlight a role for genes involved in signal transmission, embryonic cardiac development and the pathophysiology of dilated cardiomyopathy, congenital heart failure and/or sudden cardiac death. In addition, genetic susceptibility to increased heart rate is associated with altered cardiac conduction and reduced risk of sick sinus syndrome, and both heart rate–increasing and heart rate–decreasing variants associate with risk of atrial fibrillation. Our findings provide fresh insights into the mechanisms regulating heart rate and identify new therapeutic targets.
Recent genome-wide association studies found common variants near the melanocortin 4 receptor (MC4R) gene associated with obesity. This study aimed to assess the influence of the identified single nucleotide polymorphisms (SNPs) rs17782313 and rs17700633 on general and visceral adiposity in European- and African-American youth.
In 1890 youth (49.1% European-American, 45.6% male, mean age 16.7 years), we examined the associations of the rs17782313 and rs17700633 with anthropometry, percent body fat (%BF), visceral adipose tissue (VAT) and subcutaneous abdominal adipose tissue (SAAT). Interaction of the SNPs with ethnicity or gender was investigated and haplotype analyses conducted.
Rs17782313 was significantly associated with weight (P=0.02) and waist circumference (P=0.03) in all subjects, and with body mass index (P=0.002) in females. In females rs17700633 was significantly associated with %BF (P=0.001), VAT (P<0.001) and SAAT (P<0.001). Rs17700633 was significantly associated with fasting insulin and HOMA, but the significance attenuated after adjustment for %BF. These findings were confirmed by haplotype analysis. No significant interactions of the variants with ethnicity were found for any of these phenotypes.
The relatively large effect of these common variants near MC4R on general and visceral adiposity in childhood, especially in girls, could prove helpful in elucidating the molecular mechanisms underlying the development of obesity in early life.
obesity; genetics; ethnicity
This study examined genetic and environmental contributions to the individual differences in blood pressure (BP) levels and underlying hemodynamic characteristics at rest and during mental challenge tasks in a large twin cohort of youth. Including both European American (EA) and African American (AA) twins further allowed examination of potential ethnic differences.
We studied CVR to two stressors (car driving simulation and a social stressor interview) in 308 EA and 223 AA twin pairs including monozygotic twin pairs and same-sex as well as opposite-sex dizygotic twin pairs (mean [SD] age: 14.7 [3.1]). Variables included systolic and diastolic BP, heart rate (HR), stroke volume, cardiac output and total peripheral resistance.
Heritability indices for levels at rest and during stress were high (31% – 73%) and comparable between ethnic groups. A common genetic factor accounted for both resting and stress levels explaining 23% to 58% of the total variance. The increases in heritability indices for BP and HR from rest to stress are mostly explained by newly emerging genetic influences on the added stress component. Indices for hemodynamic variables remained stable from rest to stress owing to a simultaneous decrease in genetic and environmental variances.
Cardiovascular measures obtained during rest and stress show substantial heritability that is comparable between individuals of African and European descent. Most of the variance in both resting and stress levels is explained by common genetic factors, although other genetic factors that only contribute to cardiovascular levels during stress are also important.
blood pressure; hemodynamics; reactivity; heritability; ethnicity; twin
To test the hypothesis that changes in DNA methylation are involved in vitamin D deficiency–related immune cell regulation using an unbiased genome-wide approach combined with a genomic and epigenomic integrative approach.
We performed a genome-wide methylation scan using the Illumina HumanMethylation 27 BeadChip on leukocytes DNAs of 11 cases of vitamin D deficiency (serum 25(OH)D≤ 25 nmol/L) and 11 age-matched controls (serum 25(OH)D>75 nmol/L); the subjects were African American normal-weight (BMI<85th percentile) males aged 14-19 years. The Limma package was used to analyze each CpG site for differential methylation between cases and controls. To correct for multiple testing, the set of raw p values were converted to false discovery rates (FDR). We also compared our findings with the recent data from GWAS of circulating 25(OH) D levels and then performed a permutation test to examine whether the “double hit” genes were randomly enriched.
A total of 79 CpG sites achieved raw p<0.001. Of the 79 CpG sites, 2 CpG sites survived multiple testing: cg16317961 (raw p=3.5 × 10-6, FDR=0.078, in MAPRE2) and cg04623955 (raw p=5.9 × 10-6, FDR=0.078, in DIO3). Furthermore, 3 out of the 4 genes previously identified in the two GWAS studies were also significant at the methylation level (DHCR7: cg07487535, p=0.015 & cg10763288, p=0.017; CYP2R1: cg25454890, p=0.040; CYP24A1: cg18956481, p=0.022), reflecting significant enrichment (p=0.0098).
Severe vitamin D deficiency is associated with methylation changes in leukocyte DNA. The genomic and epigenomic approach reinforce the crucial roles played by the DHCR7, CYP2R1 and CYP24A1 genes in vitamin D metabolism.
Vitamin D deficiency; DNA methylation; genome-wide association study; African Americans; extreme phenotypes
Blood pressure (BP) is a heritable determinant of risk for cardiovascular disease (CVD). To investigate genetic associations with systolic BP (SBP), diastolic BP (DBP), mean arterial pressure (MAP) and pulse pressure (PP), we genotyped ∼50 000 single-nucleotide polymorphisms (SNPs) that capture variation in ∼2100 candidate genes for cardiovascular phenotypes in 61 619 individuals of European ancestry from cohort studies in the USA and Europe. We identified novel associations between rs347591 and SBP (chromosome 3p25.3, in an intron of HRH1) and between rs2169137 and DBP (chromosome1q32.1 in an intron of MDM4) and between rs2014408 and SBP (chromosome 11p15 in an intron of SOX6), previously reported to be associated with MAP. We also confirmed 10 previously known loci associated with SBP, DBP, MAP or PP (ADRB1, ATP2B1, SH2B3/ATXN2, CSK, CYP17A1, FURIN, HFE, LSP1, MTHFR, SOX6) at array-wide significance (P < 2.4 × 10−6). We then replicated these associations in an independent set of 65 886 individuals of European ancestry. The findings from expression QTL (eQTL) analysis showed associations of SNPs in the MDM4 region with MDM4 expression. We did not find any evidence of association of the two novel SNPs in MDM4 and HRH1 with sequelae of high BP including coronary artery disease (CAD), left ventricular hypertrophy (LVH) or stroke. In summary, we identified two novel loci associated with BP and confirmed multiple previously reported associations. Our findings extend our understanding of genes involved in BP regulation, some of which may eventually provide new targets for therapeutic intervention.
Approaches exploiting extremes of the trait distribution may reveal novel loci for common traits, but it is unknown whether such loci are generalizable to the general population. In a genome-wide search for loci associated with upper vs. lower 5th percentiles of body mass index, height and waist-hip ratio, as well as clinical classes of obesity including up to 263,407 European individuals, we identified four new loci (IGFBP4, H6PD, RSRC1, PPP2R2A) influencing height detected in the tails and seven new loci (HNF4G, RPTOR, GNAT2, MRPS33P4, ADCY9, HS6ST3, ZZZ3) for clinical classes of obesity. Further, we show that there is large overlap in terms of genetic structure and distribution of variants between traits based on extremes and the general population and little etiologic heterogeneity between obesity subgroups.
Our research group recently reported that aorto-radial (radial) and aorto-dorsalis-pedis (foot) pulse wave velocity (PWV) as proxies of arterial stiffness are substantially heritable in healthy youth. This paper aimed at uncovering the genetic contributions of adhesion molecules, key members in the inflammatory process, to PWV in these young individuals.
Radial and foot PWV were non-invasively measured with applanation tonometry in 702 black and white subjects (42% blacks, mean age 17.7 ±3.3 years) from the Georgia Cardiovascular Twin Study. Eight functional polymorphisms from genes for E-selectin (SELE), P-selectin (SELP), intercellular adhesion molecules-1 (ICAM1), and vascular cell adhesion molecules-1 (VCAM1) were genotyped.
Youth with Ser290Asn or Asn290Asn genotype (SELP) compared to those with Ser290Ser had an increase in both radial and foot PWV (6.61±0.07 vs. 6.41±0.05 m/s, p=0.026; 7.22±0.05 vs. 7.04±0.04 m/s, p=0.007). TT homozygotes of rs2244529 (SELP) had higher foot PWV (7.28±0.07 vs. 7.06±0.03 m/s, p=0.002) than CT heterozygotes and CC homozygotes. There appeared to be a decrease in foot PWV in youth with the 241Arg allele (ICAM1) as compared to those without (6.96±0.08 vs. 7.14±0.03 m/s, p=0.005). For the Asp693Asp (C to T) polymorphism (VCAM1), CC genotype had higher foot PWV than CT and TT genotypes (7.18±0.04 vs. 6.95±0.06 m/s, p<0.0001). There was an epistatic interaction between Ser290Asn, Gly241Arg, and Asp693Asp on foot PWV (p=0.017), explaining 3.6% variance of the foot PWV.
Genetic variation of adhesion molecules may be implicated in the development of arterial stiffness. Screening for adhesion molecule polymorphisms may help identify high-risk youth.
adhesion molecules; polymorphisms; PWV; arterial stiffness; youth
Genetic contribution to left ventricular (LV) structure is generally recognized, but whether and how this influence varies by ethnicity or with age is unknown.
Design and methods
Participants were 517 European American (EA) and African American (AA) twin pairs (mean age: 14.6 ± 3.0) at visit 1 and 422 EA and AA at follow-up 4.1 years later. Echocardiograms were obtained on both visits. Data were analyzed using structural equation modeling software Mx.
Body mass index (BMI) was a strong predictor for all LV measures at both visit 1 and 2, accounting for 3.5-24.2% of the total variance. Hemodynamics explained up to 4.5% additional LV measures variance. After adjusting for BMI, LV measures showed substantial heritability (range: 21%-71%). Best-fitting longitudinal models revealed considerable novel genetic effects on the interventricular septum, posterior wall and relative wall thickness (but not LV inner diameter), accounting for 32-41% of the phenotypic variance at visit 2, with no significant gender and ethnic effects. There was a gender difference for LV mass index in AA (P < 0.01), with a significant influence of novel genetic effects in males (47%), but not in females. No gender difference was seen in EA, with 34% of the phenotypic variance at visit 2 attributable to novel genetic effects.
The heritability of cardiac structure and geometry was equally substantial in both AA and EA. Significant novel genetic influences were detected for all measures but LV inner diameter and LV mass index in AA females. Further developmental genetic studies are warranted to elucidate the nature of the emerging gene effects during the transition from adolescence into adulthood.
heritability; left ventricular mass; ethnicity
Blood pressure variability (BPV) and its reduction in response to antihypertensive treatment are predictors of clinical outcomes; however, little is known about its heritability. In this study, we examined the relative influence of genetic and environmental sources of variance of BPV and the extent to which it may depend on race or sex in young twins.
Twins were enrolled from two studies. One study included 703 white twins (308 pairs and 87 singletons) aged 18–34 years, whereas another study included 242 white twins (108 pairs and 26 singletons) and 188 black twins (79 pairs and 30 singletons) aged 12–30 years. BPV was calculated from 24-h ambulatory blood pressure recording.
Twin modeling showed similar results in the separate analysis in both twin studies and in the meta-analysis. Familial aggregation was identified for SBP variability (SBPV) and DBP variability (DBPV) with genetic factors and common environmental factors together accounting for 18–40% and 23–31% of the total variance of SBPV and DBPV, respectively. Unique environmental factors were the largest contributor explaining up to 82–77% of the total variance of SBPV and DBPV. No sex or race difference in BPV variance components was observed. The results remained the same after adjustment for 24-h blood pressure levels.
The variance in BPV is predominantly determined by unique environment in youth and young adults, although familial aggregation due to additive genetic and/or common environment influences was also identified explaining about 25% of the variance in BPV.
blacks; blood pressure variability; heritability; meta-analysis; twin study
Prostasin, a serine protease, is suggested to be a novel mechanism regulating the epithelial sodium channel expressed in the distal nephron. This study aimed to evaluate whether the human prostasin gene is a novel candidate gene underlying blood pressure (BP) elevation.
In a sample of healthy African American (AA) and European American (EA) twin subjects aged 17.6±3.3 years (n=920, 45% AAs), race-specific tagging single nucleotide polymorphisms (tSNPs) were identified to tag all the available SNPs ± 2Kb up- and downstream of the prostasin gene from HapMap at r2 of 0.8 – 1.0. Selection yielded four tSNPs in AAs and one in EAs, with one tSNP (rs12597511: C to T) present in both AAs and EAs.
For rs12597511, CT and TT genotypes exhibited higher systolic BP than CC genotype (115.9±1.1 mmHg vs. 113.7±0.6 mmHg, p=0.025 [AAs]; and 110.7±0.5 mmHg vs. 109.6±0.6 mmHg, p=0.115 [EAs]). CT and TT genotypes compared to CC genotype showed a significant increase in diastolic BP in both racial groups (62.5±0.7 mmHg vs. 60.4±0.4 mmHg, p=0.003 [AAs]; and 58.2±0.3 mmHg vs. 56.7±0.4 mmHg, p=0.007 [EAs]). Furthermore, there was an increase in radial pulse wave velocity (PWV) in subjects with CT and TT genotype as compared to those with CC genotype (6.5±0.1 vs. 6.1±0.1 m/s, p<0.0001) [EAs]; and 6.7±0.1 vs. 6.6±0.1 m/s, p=0.354 [AAs]). Analyses combining AAs and EAs consistently demonstrated a statistical significance of rs1259751 on all the phenotypes including systolic/diastolic BP, and PWV.
Genetic variation of the prostasin gene may be implicated in the development of hypertension in youths.
Prostasin; ENaC; Polymorphisms; Blood Pressure; Arterial stiffness
A genome-wide association study of educational attainment was conducted in a discovery sample of 101,069 individuals and a replication sample of 25,490. Three independent SNPs are genome-wide significant (rs9320913, rs11584700, rs4851266), and all three replicate. Estimated effects sizes are small (R2 ≈ 0.02%), approximately 1 month of schooling per allele. A linear polygenic score from all measured SNPs accounts for ≈ 2% of the variance in both educational attainment and cognitive function. Genes in the region of the loci have previously been associated with health, cognitive, and central nervous system phenotypes, and bioinformatics analyses suggest the involvement of the anterior caudate nucleus. These findings provide promising candidate SNPs for follow-up work, and our effect size estimates can anchor power analyses in social-science genetics.
Chronic kidney disease (CKD), the result of permanent loss of kidney function, is a major global problem. We identify common genetic variants at chr2p12-p13, chr6q26, chr17q23 and chr19q13 associated with serum creatinine, a marker of kidney function (P=10−10 to 10−15). SNPs rs10206899 (near NAT8, chr2p12-p13) and rs4805834 (near SLC7A9, chr19q13) were also associated with CKD. Our findings provide new insight into metabolic, solute and drug-transport pathways underlying susceptibility to CKD.
Elevated serum urate concentrations can cause gout, a prevalent and painful inflammatory arthritis. By combining data from >140,000 individuals of European ancestry within the Global Urate Genetics Consortium (GUGC), we identified and replicated 28 genome-wide significant loci in association with serum urate concentrations (18 new regions in or near TRIM46, INHBB, SFMBT1, TMEM171, VEGFA, BAZ1B, PRKAG2, STC1, HNF4G, A1CF, ATXN2, UBE2Q2, IGF1R, NFAT5, MAF, HLF, ACVR1B-ACVRL1 and B3GNT4). Associations for many of the loci were of similar magnitude in individuals of non-European ancestry. We further characterized these loci for associations with gout, transcript expression and the fractional excretion of urate. Network analyses implicate the inhibins-activins signaling pathways and glucose metabolism in systemic urate control. New candidate genes for serum urate concentration highlight the importance of metabolic control of urate production and excretion, which may have implications for the treatment and prevention of gout.
We tested whether the heritability of heart rate variability (HRV) under stress is different from rest and its dependency on ethnicity or gender. HRV indexed by root mean square of successive differences (RMSSD) and high-frequency (HF) power was measured at rest and during 3 stressors in 427 European and 308 African American twins. No ethnic or gender differences were found for any measures. There was a nonsignificant increase in heritability of RMSSD (from 0.48 to 0.58) and HF (from 0.50 to 0.58) under stress. Up to 81% and 60% of the heritabilities of RMSSD and HF under stress could be attributed to genes influencing rest levels. The heritabilities due to genes expressed under stress were 0.11 for RMSSD and 0.23 for HF. The findings suggest that, independent of ethnicity and gender, HRV regulation at rest and under stress is largely influenced by the same genes with a small but significant contribution of stress-specific genetic effects.
Heart rate variability; Stress; Ethnicity; Twin study
To determine to what extent the genetic influences on blood pressure (BP) measured in the office, under psychologically stressful conditions in the laboratory and during real life are different from each other. Office BP, BP during a video game challenge and a social stressor interview, and 24-h ambulatory BP were measured in 238 European American and 186 African American twins. BP values across the two tasks were averaged to represent stress levels. Genetic model fitting showed no ethnic or gender differences for any of the measures. The model fitting resulted in heritability estimates of 63, 75 and 71% for office, stress and 24-h systolic BP (SBP) and 59, 67 and 69% for diastolic BP (DBP), respectively. Up to 81% of the heritability of office SBP and 71% of office DBP were attributed to genes that also influenced stress BP. However, only 45% of the heritability of 24-h SBP and 49% of 24-h DBP were attributed to genes that also influence office BP. Similarly, about 39% of the heritability of 24-h SBP and 42% of 24-h DBP were attributed to genes that also influence stress BP. Substantial overlap exists between genes that influence BP measured in the office, under laboratory stress and during real life. However, significant genetic components specific to each BP measurement also exist. These findings suggest that partly different genes or sets of genes contribute to BP regulation in different conditions.
African American; ambulatory blood pressure; heritability; stress; twin
This study evaluates the tracking stability of office blood pressure (BP), ambulatory BP (ABP), BP variability (BPV) and nocturnal BP drops (dipping) from childhood to early adulthood, and their dependence on ethnicity, gender and family history (FH) of essential hypertension (EH). Generalized estimating equations (GEEs) were used to estimate tracking coefficients for 295 European Americans and 252 African Americans, with a maximum of 12 measurements over a 15-year period. Office BP and ABP had moderate-to-relatively high tracking coefficients (r= 0.30–0.59; P≤0.001). Twenty-four hour readings tracked better than office readings for diastolic BP (DBP; 0.57 vs. 0.46, P=1.72×10−6) and pulse pressure (PP) (0.59 vs. 0.51, P=2.70×10−4), and equally well for systolic BP (SBP; 0.55 vs. 0.54, P=0.805). Daytime readings tracked better than their night-time counterparts for SBP (0.50 vs. 0.37, P=7.62×10−13), DBP (0.49 vs. 0.30, P=7.98×10−32) and PP (0.55 vs. 0.50, P=0.0061). All BPV (r=0.08–0.28; P≤0.001) and dipping measures (r=0.07–0.12; odds ratio, 1.60–1.73; P≤0.001) had low tracking coefficients. Males had significantly higher tracking stability for office SBP, DBP and ambulatory PP than females (P<0.01). Subjects with a positive FH of EH had significantly higher tracking stability for daytime and night-time DBP and dipping indexed by continuous variables than those with a negative FH (P<0.001). No significant ethnic differences were observed. The high tracking stability of 24-h ABP highlights the importance of using ambulatory BP monitoring in both research and clinical settings.
ambulatory blood pressure; blood pressure variability; dipping; longitudinal study; tracking
To examine whether the genetic influences on blood pressure (BP) during night-time are different from those during daytime and the extent to which they depend on ethnicity or sex.
Ambulatory BP was measured in 240 European–American and 190 African–American twins (mean ± SD age, 17.2 ± 3.4). Individuals with night-time BP falls more than 10% of the daytime values were defined as dippers. A bivariate analysis of the daytime and the night-time BP levels, as well as a liability-threshold model of dippers vs. nondippers were used.
Bivariate model fitting showed no ethnic or sex differences for any of the measures, with heritabilities of 0.70 and 0.68 for SBP and 0.70 and 0.64 for DBP at daytime and at night-time. The genetic influences on daytime and night-time were not significantly different for SBP or DBP. The bivariate analysis also indicated that about 56 and 33% of the heritabilities of night-time SBP and DBP could be attributed to genes that also influenced daytime levels. The specific heritabilities due to genetic effects only influencing night-time values were 0.30 for SBP and 0.43 for DBP. The heritabilities of systolic and diastolic dipping were 0.59 and 0.81, respectively.
Independent of ethnicity and sex, an overlap exists between genes that influence daytime and night-time BP, as well as a significant genetic component that is specific to the night-time BP. These findings suggest that different genes or sets of genes contribute to BP regulation at daytime and night-time.
ambulatory blood pressure monitoring; blacks; dipping; heritability; twin study
High blood pressure variability is increasingly used as a predictor of target-organ damage and cardiovascular events. However, little is known about blood pressure variability changes with age and its possible sociodemographic, anthropometric, and genetic moderators.
Twenty-four-hour ambulatory blood pressure was measured up to 12 times over a 15-year period in 344 European Americans and 297 African–Americans with an average age of 14 years at the initial visit. Blood pressure variability was indexed by the weighted 24-h standard deviation of ambulatory blood pressure recordings.
Both systolic and diastolic blood pressure variability increased with age and ambulatory blood pressure mean values. Men had higher levels of blood pressure variability (P<0.001) and showed steeper linear increase rates with age than women. African–Americans showed higher values of blood pressure variability (P<0.05) than European Americans. Body mass index and waist circumference were also associated with higher blood pressure variability levels (P< 0.001). Individuals with higher father’s education level showed lower blood pressure variability. In the full model which included all the above factors, ethnic difference in systolic blood pressure variability was no longer significant.
The results of the present study suggest that men and African–Americans have higher blood pressure variability than women and European Americans. Apart from these ethnicity and sex effects, blood pressure variability increases with increases in age (especially in men), ambulatory blood pressure mean values and adiposity as well as decreased socioeconomic status
blood pressure variability; ethnicity; longitudinal study; sex; youth