Genetic influences on daytime and night-time blood pressure: similarities and differences

Association of genetically-predicted placental gene expression with adult blood pressure traits

OBJECTIVE

Blood pressure is a complex, polygenic trait, and the need to identify prehypertensive risks and new gene targets for blood pressure control therapies or prevention continues. We hypothesize a developmental origins model of blood pressure traits through the life course where the placenta is a conduit mediating genomic and nongenomic transmission of disease risk. Genetic control of placental gene expression has recently been described through expression quantitative trait loci (eQTL) studies which have identified associations with childhood phenotypes.

METHODS

We conducted a transcriptome-wide gene expression analysis estimating the predicted gene expression of placental tissue in adult individuals with genome-wide association study (GWAS) blood pressure summary statistics. We constructed predicted expression models of 15 154 genes from reference placenta eQTL data and investigated whether genetically-predicted gene expression in placental tissue is associated with blood pressure traits using published GWAS summary statistics. Functional annotation of significant genes was generated using FUMA.

RESULTS

We identified 18, 9, and 21 genes where predicted expression in placenta was significantly associated with systolic blood pressure (SBP), diastolic blood pressure (DBP), and pulse pressure (PP), respectively. There were 14 gene-tissue associations (13 unique genes) significant only in placenta.

CONCLUSIONS

In this meta-analysis using S-PrediXcan and GWAS summary statistics, the predicted expression in placenta of 48 genes was statistically significantly associated with blood pressure traits. Notable findings included the association of FGFR1 expression with increased SBP and PP. This evidence of gene expression variation in placenta preceding the onset of adult blood pressure phenotypes is an example of extreme preclinical biological changes which may benefit from intervention.

Toward Precision Medicine: Circadian Rhythm of Blood Pressure and Chronotherapy for Hypertension - 2021 NHLBI Workshop Report

Healthy individuals exhibit blood pressure variation over a 24-hour period with higher blood pressure during wakefulness and lower blood pressure during sleep. Loss or disruption of the blood pressure circadian rhythm has been linked to adverse health outcomes, for example, cardiovascular disease, dementia, and chronic kidney disease. However, the current diagnostic and therapeutic approaches lack sufficient attention to the circadian rhythmicity of blood pressure. Sleep patterns, hormone release, eating habits, digestion, body temperature, renal and cardiovascular function, and other important host functions as well as gut microbiota exhibit circadian rhythms, and influence circadian rhythms of blood pressure. Potential benefits of nonpharmacologic interventions such as meal timing, and pharmacologic chronotherapeutic interventions, such as the bedtime administration of antihypertensive medications, have recently been suggested in some studies. However, the mechanisms underlying circadian rhythm-mediated blood pressure regulation and the efficacy of chronotherapy in hypertension remain unclear. This review summarizes the results of the National Heart, Lung, and Blood Institute workshop convened on October 27 to 29, 2021 to assess knowledge gaps and research opportunities in the study of circadian rhythm of blood pressure and chronotherapy for hypertension.

Ethnic differences and heritability of blood pressure circadian rhythm in African and European American youth and young adults

BACKGROUND

The aim of this study was to investigate whether blood pressure (BP) circadian rhythm in African Americans differed from that in European Americans. We further examined the genetic and/or environmental sources of variances of the BP circadian rhythm parameters and the extent to which they depend on ethnicity or sex.

METHOD

Quantification of BP circadian rhythm was obtained using Fourier transformation from the ambulatory BP monitoring data of 760 individuals (mean age, 17.2 ± 3.3; 322 twin pairs and 116 singletons; 351 African Americans).

RESULTS

BP circadian rhythm showed a clear difference by ethnic group with African Americans having a lower amplitude (P = 1.5e-08), a lower percentage rhythm (P = 2.8e-11), a higher MESOR (P = 2.5e-05) and being more likely not to display circadian rhythm (P = 0.002) or not in phase (P = 0.003). Familial aggregation was identified for amplitude, percentage rhythm and acrophase with genetic factors and common environmental factors together accounting for 23 to 33% of the total variance of these BP circadian rhythm parameters. Unique environmental factors were the largest contributor explaining up to 67--77% of the total variance of these parameters. No sex or ethnicity difference in the variance components of BP circadian rhythm was observed.

CONCLUSION

This study suggests that ethnic differences in BP circadian rhythm already exist in youth with African Americans having a dampened circadian rhythm and better BP circadian rhythm may be achieved by changes in environmental factors.

Vitamin A deficiency indicating as low expression of LRAT may be a novel biomarker of primary hypertension

AIMS

Vitamin A (VA) deficiency triggers many diseases and is a worldwide nutrition problem. The Retinol acyltransferase (LRAT) is an indicator of VA storage function, and the relationship between LRAT and blood pressure level and the regulation mechanism will be elucidated.

METHODS

160 children aged 6-12 years were included, and the serum VA and, the transcription levels of LRAT and RARs, were measured. Spontaneously hypertensive rats (SHRs) and WKY rats were treated with VA deficiency (VAD) or normal (VAN) fodder for 20 weeks. LRAT, retinoic acid, renin angiotensin system (RAS) biomarkers, and the structure and function of the heart for SHRs were measured.

RESULTS

The serum retinol and serum retinol/BMI levels were lower in children in the low LRAT group (LRAT<P₅₀) compared with the high LRAT group (LRAT≥P₅₀)(0.82 μmol/L vs. 0.94 μmol/L, 0.04 vs. 0.05, all P < .01). Moreover, SBP, DBP, and Ang Ⅱ were lower in the low LRAT group (all P < .01). Compared with VAN-treated SHRs, LRAT, retinoic acid receptor alpha (RARα), ACE2, and Ang (1-7) protein expression levels were decreased, while ACE and AT1R expression levels were increased in VAD SHRs. Notably, heart weight (HW), left ventricle weight, the HW-to-body weight ratio and the left ventricle weight-to-body weight ratio were significantly increased in VAD SHRs compared with those in VAN SHRs (P < .01). Cardiomyocyte hypertrophy and ventricular fibrosis were significantly increased in VAD SHRs compared with those in VAN SHRs (both P < .01).

CONCLUSIONS

LRAT may be an important biomarker of vitamin A deficiency in target organs and may regulate BP by affecting RAS biomarkers.

Heritability and genetic correlations of obesity indices with ambulatory and office beat-to-beat blood pressure in the Oman Family Study

OBJECTIVE

To more precisely and comprehensively estimate the genetic and environmental correlations between various indices of obesity and BP.

METHODS

We estimated heritability and genetic correlations of obesity indices with BP in the Oman family study (n = 1231). Ambulatory and office beat-to-beat BP was measured and mean values for SBP and DBP during daytime, sleep, 24-h and 10 min at rest were calculated. Different indices were used to quantify obesity and fat distribution: BMI, percentage of body fat (%BF), waist circumference and waist-to-height ratio (WHtR). SOLAR software was used to perform univariate and bivariate quantitative genetic analyses adjusting for age, age, sex, age-sex and age--sex interactions.

RESULTS

Heritabilities of BP ranged from 30.2 to 38.2% for ambulatory daytime, 16.8--21.4% for sleeping time, 32.1--40.4% for 24-h and 22--24.4% for office beat-to-beat measurements. Heritabilities for obesity indices were 67.8% for BMI, 52.2% for %BF, 37.3% for waist circumference and 37.9% for WHtR. All obesity measures had consistently positive phenotypic correlations with ambulatory and office beat-to-beat SBP and DBP (r-range: 0.14--0.32). Genetic correlations of obesity indices with SBP and DBP were higher than environmental correlations (rG: 0.16--0.50; rE: 0.01--0.31).

CONCLUSION

The considerable genetic overlap between a variety of obesity indices and both ambulatory and office beat-to-beat BP highlights the relevance of pleiotropic genes. Future GWAS analyses should discover the specific genes both influencing obesity indices and BP to help unravel their shared genetic background.

Heritability and genetic and environmental correlations of heart rate variability and baroreceptor reflex sensitivity with ambulatory and beat-to-beat blood pressure

This family study from Oman (n = 1231) explored the heritability and genetic and environmental correlations of heart rate variability (HRV) and baroreceptor reflex sensitivity (BRS) with ambulatory and beat-to-beat blood pressure (BP). Ambulatory BP was measured for 24 hours to calculate mean values for daytime and sleep separately. Time and frequency domain HRV indices, BRS, office beat-to-beat BP, and heart rate (HR) were measured for 10 minutes at rest. SOLAR software was used to perform univariate and bivariate quantitative genetic analyses adjusting for age, age², sex, their interactions and BMI. Heritability of SBP and DBP ranged from 16.8% to 40.4% for daytime, sleeping, 24-hour and office beat-to-beat measurements. HR and BRS showed a heritability of 31.9% and 20.6%, respectively, and for HRV indices heritability ranged from 11.1% to 20.5%. All HRV measurements and BRS were found to be negatively correlated with BP, but phenotypic correlation coefficients were relatively weak; HR was positively correlated with BP. None of the genetic correlations were statistically significant while environmental factors explained most of the correlations for all HRV indices with BP. Our study found consistent but weak correlations among HRV, HR, BRS and ambulatory/office beat-to-beat BP. However, environmental rather than genetic factors contributed most to those correlations.

Genome-wide association study of nocturnal blood pressure dipping in hypertensive patients

Background

Reduced nocturnal fall (non-dipping) of blood pressure (BP) is a predictor of cardiovascular target organ damage. No genome-wide association studies (GWAS) on BP dipping have been previously reported.

Methods

To study genetic variation affecting BP dipping, we conducted a GWAS in Genetics of Drug Responsiveness in Essential Hypertension (GENRES) cohort (n = 204) using the mean night-to-day BP ratio from up to four ambulatory BP recordings conducted on placebo. Associations with P < 1 × 10^− 5 were further tested in two independent cohorts: Haemodynamics in Primary and Secondary Hypertension (DYNAMIC) (n = 183) and Dietary, Lifestyle and Genetic determinants of Obesity and Metabolic Syndrome (DILGOM) (n = 180). We also tested the genome-wide significant single nucleotide polymorphism (SNP) for association with left ventricular hypertrophy in GENRES.

Results

In GENRES GWAS, rs4905794 near BCL11B achieved genome-wide significance (β = − 4.8%, P = 9.6 × 10^− 9 for systolic and β = − 4.3%, P = 2.2 × 10^− 6 for diastolic night-to-day BP ratio). Seven additional SNPs in five loci had P values < 1 × 10^− 5. The association of rs4905794 did not significantly replicate, even though in DYNAMIC the effect was in the same direction (β = − 0.8%, P = 0.4 for systolic and β = − 1.6%, P = 0.13 for diastolic night-to-day BP ratio). In GENRES, the associations remained significant even during administration of four different antihypertensive drugs. In separate analysis in GENRES, rs4905794 was associated with echocardiographic left ventricular mass (β = − 7.6 g/m², P = 0.02).

Conclusions

rs4905794 near BCL11B showed evidence for association with nocturnal BP dipping. It also associated with left ventricular mass in GENRES. Combined with earlier data, our results provide support to the idea that BCL11B could play a role in cardiovascular pathophysiology.

Electronic supplementary material

The online version of this article (10.1186/s12881-018-0624-7) contains supplementary material, which is available to authorized users.

Associations of Urinary Caffeine and Caffeine Metabolites With Arterial Stiffness in a Large Population-Based Study

OBJECTIVE

To assess the influence of caffeine on arterial stiffness by exploring the association of urinary excretion of caffeine and its related metabolites with pulse pressure (PP) and pulse wave velocity (PWV).

PARTICIPANTS AND METHODS

Families were randomly selected from the general population of 3 Swiss cities from November 25, 2009, through April 4, 2013. Pulse pressure was defined as the difference between the systolic and diastolic blood pressures obtained by 24-hour ambulatory monitoring. Carotid-femoral PWV was determined by applanation tonometry. Urinary caffeine, paraxanthine, theophylline, and theobromine excretions were measured in 24-hour urine collections. Multivariate linear and logistic mixed models were used to explore the associations of quartiles of urinary caffeine and metabolite excretions with PP, high PP, and PWV.

RESULTS

We included 863 participants with a mean ± SD age of 47.1±17.6 years, 24-hour PP of 41.9±9.2 mm Hg, and PWV of 8.0±2.3 m/s. Mean (SE) brachial PP decreased from 43.5 (0.5) to 40.5 (0.6) mm Hg from the lowest to the highest quartiles of 24-hour urinary caffeine excretion (P<.001). The odds ratio (95% CI) of high PP decreased linearly from 1.0 to 0.52 (0.31-0.89), 0.38 (0.22-0.65), and 0.31 (0.18-0.55) from the lowest to the highest quartile of 24-hour urinary caffeine excretion (P<.001). Mean (SE) PWV in the highest caffeine excretion quartile was significantly lower than in the lowest quartile (7.8 [0.1] vs 8.1 [0.1] m/s; P=.03). Similar associations were found for paraxanthine and theophylline, whereas no associations were found with theobromine.

CONCLUSION

Urinary caffeine, paraxanthine, and theophylline excretions were associated with decreased parameters of arterial stiffness, suggesting a protective effect of caffeine intake beyond its blood pressure-lowering effect.

Genetic and Environmental Effects on Gene Expression Signatures of Blood Pressure: A Transcriptome-Wide Twin Study

Recently, 2 transcriptome-wide studies identified 40 genes that were differentially expressed in relation to blood pressure. However, to what extent these BP-related gene expression signatures and their associations with BP are driven by genetic or environmental factors has not been investigated. In this study of 391 twins (193 twin pairs and 5 singletons; age 55-69 years; 40% male; 57% monozygous) recruited from the Finnish Twin Cohort, transcriptome-wide data on peripheral leukocytes were obtained using the Illumina HT12 V4 array. Our transcriptome-wide analysis identified 1 gene (MOK [MAPK/MAK/MRK overlapping kinase], P=7.16×10-8) with its expression levels associated with systolic BP at the cutoff of false-discovery rate <0.05. This association was further replicated in the Framingham Heart Study (P=1.02×10-5). Out of the 40 genes previously reported, 12 genes could be replicated in the twin cohort with false-discovery rate <0.05 and consistent direction of effect. Univariate twin modeling showed that genetic factors contributed to the expression variations of 12 genes with heritability estimates ranging from 6% to 65%. Bivariate twin modeling showed that 53% of the phenotypic association between systolic BP and MOK expression, and 100% of the phenotypic association of systolic and diastolic BP with CD97 (cluster of differentiation 97), TIPARP (TCDD-inducible poly[ADP-ribose] polymerase), and TPPP3 expression could be explained by genetic factors shared in common. In this study of adult twins, we identified one more gene, MOK, with its expression level associated with BP, and replicated several previously identified signals. Our study further provides new insights into the genetic and environmental sources of BP-related gene expression signatures.

Sympathetic Nerve Activity in Monozygotic Twins

Microneurographic recordings of human muscle sympathetic nerve activity responses to sudden sensory stimuli (ie, arousal) have revealed 2 intraindividually reproducible response profiles in healthy young males that predict different neural and blood pressure responses to more sustained stress. Approximately 50% of subjects inhibit muscle sympathetic nerve activity during arousal, whereas the remaining 50% do not, and the latter group displays a markedly greater blood pressure increase in response to arousal, as well as during and after 3 minutes of mental arithmetic. Studying a group of monozygotic twins (10 pairs, 2 excluded from analysis), the aim of the present study was to evaluate the degree of genetic determination of these sympathetic response profiles. Muscle sympathetic burst incidence at rest was similar in twins, with a within-pair burst incidence ratio of 0.87±0.02 (SEM) compared with 0.73±0.07 found in unrelated pairs ( P =0.002), confirming a previous study from our laboratory. In contrast, the sympathetic responses to arousal showed large twin within-pair variance (arousal inhibition ratio 0.56±0.11), which did not significantly differ ( P =0.939) from the variance in pairs of unrelated subjects (0.46±0.11). The finding that human muscle sympathetic nerve responses to arousal are less determined by genotype than the resting level of corresponding sympathetic nerve activity suggests that the arousal response pattern is more prone to be altered by environmental factors. This raises the possibility that these intraindividually reproducible sympathetic neural response profiles can be modified in a positive direction from a cardiovascular risk perspective.

The Relationship Between Gene Polymorphisms and Dipping Profile in Patients With Coronary Heart Disease

BACKGROUND

The aim of this study is to report the relationship between certain single-nucleotide polymorphisms (SNPs) and blunted nighttime blood pressure (BP) fall in patients with coronary artery disease confirmed by coronary angiography.

METHODS

According to the percentage decrease in mean systolic BP (SBP) and diastolic BP (DBP) during the nighttime period, subjects were classified as dippers or nondippers (nighttime relative SBP or DBP decline ≥10% and <10%, respectively). Genetic risk score (GRS18) was constructed to evaluate additive effect of 18 SNPs for nondipping status.

RESULTS

In the present study, 1,345 subjects with coronary heart disease (CHD) were included. During follow-up period (median 8.3 years, interquartile range 5.3-9.0 years), there were 245 all-cause deaths (18.2%) including 114 cardiovascular deaths (8.5%). There were significant differences in the number of revascularizations between nondippers SBP and DBP and dippers SBP and DBP (48.0% vs. 36.4%, P < 0.01). SNPs of the genes, MIA3, MRAS, PCSK9, SMG6, and ZC3HC1, were related to a higher risk of nondipping SBP and DBP status.

CONCLUSIONS

In the present study, polymorphisms of genes related to CHD (MIA3, MRAS, PCSK9, SMG6, and ZC3HC1) were associated with nondipping SBP and DBP profile, and GRS18 was associated with nondipping status. In addition, this profile was related to a higher risk of revascularization.

Heritability of ambulatory and office blood pressure in the Swiss population

BACKGROUND

Blood pressure (BP) is known to aggregate in families. Yet, heritability estimates are population-specific and no Swiss data have been published so far. We estimated the heritability of ambulatory and office BP in a Swiss population-based sample.

METHODS

The Swiss Kidney Project on Genes in Hypertension is a population-based family study focusing on BP genetics. Office and ambulatory BP were measured in 1009 individuals from 271 nuclear families. Heritability was estimated for SBP, DBP, and pulse pressure using a maximum likelihood method implanted in the Statistical Analysis in Genetic Epidemiology software.

RESULTS

The 518 women and 491 men included in this analysis had a mean (±SD) age of 48.3 (±17.4) and 47.3 (±17.7) years, and a mean BMI of 23.8 (±4.2) and 25.9 (±4.1) kg/m, respectively. Narrow-sense heritability estimates (±standard error) for ambulatory SBP, DBP, and pulse pressure were 0.37 ± 0.07, 0.26 ± 0.07, and 0.29 ± 0.07 for 24-h BP; 0.39 ± 0.07, 0.28 ± 0.07, and 0.27 ± 0.07 for day BP; and 0.25 ± 0.07, 0.20 ± 0.07, and 0.30 ± 0.07 for night BP, respectively (all P < 0.001). Heritability estimates for office SBP, DBP, and pulse pressure were 0.21 ± 0.08, 0.25 ± 0.08, and 0.18 ± 0.07 (all P < 0.01).

CONCLUSIONS

We found significant heritability estimates for both ambulatory and office BP in this Swiss population-based study. Our findings justify the ongoing search for the genetic determinants of BP.

International Genome-Wide Association Study Consortium Identifies Novel Loci Associated With Blood Pressure in Children and Adolescents

BACKGROUND

Our aim was to identify genetic variants associated with blood pressure (BP) in childhood and adolescence.

METHODS AND RESULTS

Genome-wide association study data from participating European ancestry cohorts of the Early Genetics and Lifecourse Epidemiology (EAGLE) Consortium was meta-analyzed across 3 epochs; prepuberty (4-7 years), puberty (8-12 years), and postpuberty (13-20 years). Two novel loci were identified as having genome-wide associations with systolic BP across specific age epochs: rs1563894 (ITGA11, located in active H3K27Ac mark and transcription factor chromatin immunoprecipitation and 5'-C-phosphate-G-3' methylation site) during prepuberty (P=2.86×10(-8)) and rs872256 during puberty (P=8.67×10(-9)). Several single-nucleotide polymorphism clusters were also associated with childhood BP at P<5×10(-3). Using a P value threshold of <5×10(-3), we found some overlap in variants across the different age epochs within our study and between several single-nucleotide polymorphisms in any of the 3 epochs and adult BP-related single-nucleotide polymorphisms.

CONCLUSIONS

Our results suggest that genetic determinants of BP act from childhood, develop over the lifecourse, and show some evidence of age-specific effects.

Determinants of day-night difference in blood pressure, a comparison with determinants of daytime and night-time blood pressure

Blunted day–night difference in blood pressure (BP) is an independent cardiovascular risk factor, although there is limited information on determinants of diurnal variation in BP. We investigated determinants of day–night difference in systolic (SBP) and diastolic (DBP) BP and how these compared with determinants of daytime and night-time SBP and DBP. We analysed the association of mean daytime, mean night-time and mean day–night difference (defined as (mean daytime−mean night-time)/mean daytime) in SBP and DBP with clinical, lifestyle and biochemical parameters from 1562 adult individuals (mean age 38.6) from 509 nuclear families recruited in the GRAPHIC Study. We estimated the heritability of the various BP phenotypes. In multivariate analysis, there were significant associations of age, sex, markers of adiposity (body mass index and waist–hip ratio), plasma lipids (total and low-density lipoprotein cholesterol and triglycerides), serum uric acid, alcohol intake and current smoking status on daytime or night-time SBP and/or DBP. Of these, only age (P=4.7 × 10⁻⁵), total cholesterol (P=0.002), plasma triglycerides (P=0.006) and current smoking (P=3.8 × 10⁻⁹) associated with day–night difference in SBP, and age (P=0.001), plasma triglyceride (P=2.2 × 10⁻⁵) and current smoking (3.8 × 10⁻⁴) associated with day–night difference in DBP. 24-h, daytime and night-time SBP and DBP showed substantial heritability (ranging from 18–43%). In contrast day–night difference in SBP showed a lower heritability (13%) while heritability of day–night difference in DBP was not significant. These data suggest that specific clinical, lifestyle and biochemical factors contribute to inter-individual variation in daytime, night-time and day–night differences in SBP and DBP. Variation in day–night differences in BP is largely non-genetic.

Familial aggregation and childhood blood pressure

There is growing concern about elevated blood pressure (BP) in children. The evidence for familial aggregation of childhood BP is substantial. Twin studies have shown that a large part of the familial aggregation of childhood BP is due to genes. The first part of this review provides the latest progress in gene finding for childhood BP, focusing on the combined effects of multiple loci identified from the genome-wide association studies on adult BP. We further review the evidence on the contribution of the genetic components of other family risk factors to the familial aggregation of childhood BP including obesity, birth weight, sleep quality, sodium intake, parental smoking, and socioeconomic status. At the end, we emphasize the promise of using genomic-relatedness-matrix restricted maximum likelihood (GREML) analysis, a method that uses genome-wide data from unrelated individuals, in answering a number of unsolved questions in the familial aggregation of childhood BP.

Specific genetic influences on nighttime blood pressure

OBJECTIVES

Nighttime blood pressure (BP) has been shown to be superior to daytime BP in predicting hypertension related target organ damage and cardiac mortality. In our Georgia Cardiovascular Twin Study, we showed that apart from the genes that also influence daytime BP, specific genetic determinants explained 44% and 67% of the nighttime systolic BP (SBP) and diastolic BP (DBP) heritabilities, respectively. Here, we determined whether these results could be confirmed in a much larger twin cohort of young adults with 24-hour ambulatory BP measurements.

METHODS

Ambulatory BP was available in 703 white twins (308 pairs and 87 singletons, aged 18-34 years, 50% males) from the Prenatal Programming Twin Study. A bivariate quantitative genetic twin model was used to analyze daytime and nighttime BP. We conducted a meta-analysis to compare and integrate results from the 2 twin cohorts.

RESULTS

Model fitting showed no sex differences for any of the measures. Heritabilities were 0.60 and 0.51 for SBP and 0.54 and 0.46 for DBP at daytime and nighttime. The specific heritability due to novel genetic effects emerging during the nighttime was 0.21 for SBP and 0.26 for DBP, which comprised 41% and 57% of the total nighttime heritability for SBP and DBP, respectively. Meta-analysis confirmed absence of cohort differences with very similar combined results.

CONCLUSIONS

In addition to genes that influence both daytime and nighttime BP, a large part of the heritability is explained by genes that specifically influence BP at night.

Associations of ambulatory blood pressure with urinary caffeine and caffeine metabolite excretions

Intake of caffeinated beverages might be associated with reduced cardiovascular mortality possibly via the lowering of blood pressure. We estimated the association of ambulatory blood pressure with urinary caffeine and caffeine metabolites in a population-based sample. Families were randomly selected from the general population of Swiss cities. Ambulatory blood pressure monitoring was conducted using validated devices. Urinary caffeine, paraxanthine, theophylline, and theobromine excretions were measured in 24 hours urine using ultrahigh performance liquid chromatography tandem mass spectrometry. We used mixed models to explore the associations of urinary excretions with blood pressure although adjusting for major confounders. The 836 participants (48.9% men) included in this analysis had mean age of 47.8 and mean 24-hour systolic and diastolic blood pressure of 120.1 and 78.0 mm Hg. For each doubling of caffeine excretion, 24-hour and night-time systolic blood pressure decreased by 0.642 and 1.107 mm Hg (both P values <0.040). Similar inverse associations were observed for paraxanthine and theophylline. Adjusted night-time systolic blood pressure in the first (lowest), second, third, and fourth (highest) quartile of paraxanthine urinary excretions were 110.3, 107.3, 107.3, and 105.1 mm Hg, respectively (P trend <0.05). No associations of urinary excretions with diastolic blood pressure were generally found, and theobromine excretion was not associated with blood pressure. Anti-hypertensive therapy, diabetes mellitus, and alcohol consumption modify the association of caffeine urinary excretion with systolic blood pressure. Ambulatory systolic blood pressure was inversely associated with urinary excretions of caffeine and other caffeine metabolites. Our results are compatible with a potential protective effect of caffeine on blood pressure.

A novel SNP associated with nighttime pulse pressure in young-onset hypertension patients could be a genetic prognostic factor for cardiovascular events in a general cohort in Taiwan

Background

Pulse pressure (PP) is a risk factor for cardiovascular disease. It has been reported that ambulatory blood pressure (BP) and nighttime BP parameters are heritable traits. However, the genetic association of pulse pressure and its clinical impact remain undetermined.

Method and Results

We conducted a genome-wide association study of PP using ambulatory BP monitoring in young-onset hypertensive patients and found a significant association between nighttime PP and SNP rs897876 (p = 0.009) at chromosome 2p14, which contains the predicted gene FLJ16124. Young-onset hypertension patients carrying TT genotypes at rs897876 had higher nighttime PP than those with CT and CC genotypes (TT, 41.6±7.3 mm Hg; CT, 39.1±6.0 mm Hg; CC, 38.9±6.3 mm Hg; p<0.05,). The T risk allele resulted in a cumulative increase in nighttime PP (β = 1.036 mm Hg, se. = 0.298, p<0.001 per T allele). An independent community-based cohort containing 3325 Taiwanese individuals (mean age, 50.2 years) was studied to investigate the genetic impact of rs897876 polymorphisms in determining future cardiovascular events. After an average 7.79±0.28 years of follow-up, the TT genotype of rs897876 was independently associated with an increased risk (in a recessive model) of coronary artery disease (HR, 2.20; 95% CI, 1.20–4.03; p = 0.01) and total cardiovascular events (HR, 1.99; 95% CI, 1.29–3.06; p = 0.002), suggesting that the TT genotype of rs897876C, which is associated with nighttime pulse pressure in young-onset hypertension patients, could be a genetic prognostic factor of cardiovascular events in the general cohort.

Conclusion

The TT genotype of rs897876C at 2p14 identified in young-onset hypertensive had higher nighttime PP and could be a genetic prognostic factor of cardiovascular events in the general cohort in Taiwan.

Genetic and environmental influences on blood pressure variability: a study in twins

OBJECTIVES

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.

METHODS

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.

RESULTS

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.

CONCLUSIONS

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.

Heritability of ambulatory and beat-to-beat office blood pressure in large multigenerational Arab pedigrees: the 'Oman Family study'

OBJECTIVE

To estimate the heritability of ambulatory blood pressure (BP), heart rate (HR), and beat-to-beat office BP and HR in an isolated, environmentally and genetically homogeneous Omani Arab population.

METHODS

Ambulatory BP measurements were recorded in 1,124 subjects with a mean age of 33.8 ± 16.2 years, using the auscultatory mode of the validated Schiller ambulatory BP Monitor. Beat-to-beat BP and HR were recorded by the Task Force Monitor. Heritability was estimated using quantitative genetic analysis. This was achieved by applying the maximum-likelihood-based variance decomposition method implemented in SOLAR software.

RESULTS

We detected statistically significant heritability estimates for office beat-to-beat, 24-hour, daytime, and sleep HR of 0.31, 0.21, 0.20, and 0.07, respectively. Heritability estimates in the above mentioned conditions for systolic BP (SBP)/diastolic BP (DBP)/mean BP (MBP)were all significant and estimated at 0.19/0.19/0.19, 0.30/0.44/0.41, 0.28/0.38/0.39, and 0.21/0.18/0.20,respectively. Heritability estimates for 24-hour and daytime ambulatory SBP, DBP, and MBP ranged from 0.28 to 0.44, and were higher than the heritability estimates for beat-to-beat recordings and sleep periods,which were estimated within a narrow range of 0.18-0.21.

CONCLUSION

In this cohort, because shared environments are common to all, the environmental influence that occurs is primarily due to the variation in non-shared environment that is unique to the individual. We demonstrated significant heritability estimates for both beat-to-beat office and ambulatory BP and HR recordings, but 24-hour and daytime ambulatory heritabilities are higher than those from beat-to-beat resting levels and ambulatory night-time recordings.