Genetic effect on blood pressure is modulated by age: the Hypertension Genetic Epidemiology Network Study

LDER-GE estimates phenotypic variance component of gene-environment interactions in human complex traits accurately with GE interaction summary statistics and full LD information

Gene-environment (GE) interactions are essential in understanding human complex traits. Identifying these interactions is necessary for deciphering the biological basis of such traits. In this study, we review state-of-art methods for estimating the proportion of phenotypic variance explained by genome-wide GE interactions and introduce a novel statistical method Linkage-Disequilibrium Eigenvalue Regression for Gene-Environment interactions (LDER-GE). LDER-GE improves the accuracy of estimating the phenotypic variance component explained by genome-wide GE interactions using large-scale biobank association summary statistics. LDER-GE leverages the complete Linkage Disequilibrium (LD) matrix, as opposed to only the diagonal squared LD matrix utilized by LDSC (Linkage Disequilibrium Score)-based methods. Our extensive simulation studies demonstrate that LDER-GE performs better than LDSC-based approaches by enhancing statistical efficiency by ~23%. This improvement is equivalent to a sample size increase of around 51%. Additionally, LDER-GE effectively controls type-I error rate and produces unbiased results. We conducted an analysis using UK Biobank data, comprising 307 259 unrelated European-Ancestry subjects and 966 766 variants, across 217 environmental covariate-phenotype (E-Y) pairs. LDER-GE identified 34 significant E-Y pairs while LDSC-based method only identified 23 significant E-Y pairs with 22 overlapped with LDER-GE. Furthermore, we employed LDER-GE to estimate the aggregated variance component attributed to multiple GE interactions, leading to an increase in the explained phenotypic variance with GE interactions compared to considering main genetic effects only. Our results suggest the importance of impacts of GE interactions on human complex traits.

Genome-wide pleiotropy analysis identifies novel blood pressure variants and improves its polygenic risk scores

Systolic and diastolic blood pressure (S/DBP) are highly correlated modifiable risk factors for cardiovascular disease (CVD). We report here a bidirectional Mendelian Randomization (MR) and horizontal pleiotropy analysis of S/DBP summary statistics from the UK Biobank (UKB)-International Consortium for Blood Pressure (ICBP) (UKB-ICBP) BP genome-wide association study and construct a composite genetic risk score (GRS) by including pleiotropic variants. The composite GRS captures greater (1.11-3.26 fold) heritability for BP traits and increases (1.09- and 2.01-fold) Nagelkerke's R² for hypertension and CVD. We replicated 118 novel BP horizontal pleiotropic variants including 18 novel BP loci using summary statistics from the Million Veteran Program (MVP) study. An additional 219 novel BP signals and 40 novel loci were identified after a meta-analysis of the UKB-ICBP and MVP summary statistics but without further independent replication. Our study provides further insight into BP regulation and provides a novel way to construct a GRS by including pleiotropic variants for other complex diseases.

Mendelian Randomization With Repeated Measures of a Time-varying Exposure: An Application of Structural Mean Models

Mendelian randomization (MR) is often used to estimate effects of time-varying exposures on health outcomes using observational data. However, MR studies typically use a single measurement of exposure and apply conventional instrumental variable (IV) methods designed to handle time-fixed exposures. As such, MR effect estimates for time-varying exposures are often biased, and interpretations are unclear. We describe the instrumental conditions required for IV estimation with a time-varying exposure, and the additional conditions required to causally interpret MR estimates as a point effect, a period effect or a lifetime effect depending on whether researchers have measurements at a single or multiple time points. We propose methods to incorporate time-varying exposures in MR analyses based on g-estimation of structural mean models, and demonstrate its application by estimating the period effect of alcohol intake, high-density lipoprotein cholesterol and low-density lipoprotein cholesterol on intermediate coronary heart disease outcomes using data from the Framingham Heart Study. We use this data example to highlight the challenges of interpreting MR estimates as causal effects, and describe other extensions of structural mean models for more complex data scenarios.

Replication of European hypertension associations in a case-control study of 9,534 African Americans

Objective

Hypertension is more prevalent in African Americans (AA) than other ethnic groups. Genome-wide association studies (GWAS) have identified loci associated with hypertension and other cardio-metabolic traits like type 2 diabetes, coronary artery disease, and body mass index (BMI), however the AA population is underrepresented in these studies. In this study, we examined a large AA cohort for the generalizability of 14 Metabochip array SNPs with previously reported European hypertension associations.

Methods

To evaluate associations, we analyzed genotype data of 14 SNPs for their associations with a diagnosis of hypertension, systolic blood pressure (SBP), and diastolic blood pressure (DBP) in a case-control study of an AA population (N = 9,534). We also performed an age-stratified analysis (>30, 30≥59 and ≥60 years) following the hypertension definition described by the 8th Joint National Committee (JNC). Associations were adjusted for BMI, age, age², sex, clinical confounders, and genetic ancestry using multivariable regression models to estimate odds ratios (ORs) and beta-coefficients. Analyses stratified by sex were also conducted. Meta-analyses (including both BioVU and COGENT-BP cohorts) were performed using a random-effects model.

Results

We found rs880315 to be associated with systolic hypertension (SBP≥140 mmHg) in the entire cohort (OR = 1.14, p = 0.003) and within women only (OR = 1.16, p = 0.012). Variant rs17080093 associated with lower SBP and DBP (β = -2.99, p = 0.0352 and - β = 1.69, p = 0.0184) among younger individuals, particularly in younger women (β = -3.92, p = 0.0025 and β = -1.87, p = 0.0241 for SBP and DBP respectively). SNP rs1530440 associated with higher SBP and DBP measurements (younger individuals β = 4.1, p = 0.039 and β = 2.5, p = 0.043 for SBP and DBP; (younger women β = 4.5, p = 0.025 and β = 2.9, p = 0.028 for SBP and DBP), and hypertension risk in older women (OR = 1.4, p = 0.050). rs16948048 increases hypertension risk in younger individuals (OR = 1.31, p = 0.011). Among mid-age women rs880315 associated with higher risk of hypertension (OR = 1.20, p = 0.027). rs1361831 associated with DBP (β = -1.96, p = 0.02) among individuals older than 60 years. rs3096277 increases hypertension risk among older individuals (OR = 1.26 p = 0.0015), however, this variant also reduces SBP among younger women (β = -2.63, p = 0.0102).

Conclusion

These findings suggest that European-descent and AA populations share genetic loci that contribute to blood pressure traits and hypertension. However, the OR and beta-coefficient estimates differ, and some are age-dependent. Additional genetic studies of hypertension in AA are warranted to identify new loci associated with hypertension and blood pressure traits in this population.

The impact of age on genetic risk for common diseases

Inherited genetic variation contributes to individual risk for many complex diseases and is increasingly being used for predictive patient stratification. Previous work has shown that genetic factors are not equally relevant to human traits across age and other contexts, though the reasons for such variation are not clear. Here, we introduce methods to infer the form of the longitudinal relationship between genetic relative risk for disease and age and to test whether all genetic risk factors behave similarly. We use a proportional hazards model within an interval-based censoring methodology to estimate age-varying individual variant contributions to genetic relative risk for 24 common diseases within the British ancestry subset of UK Biobank, applying a Bayesian clustering approach to group variants by their relative risk profile over age and permutation tests for age dependency and multiplicity of profiles. We find evidence for age-varying relative risk profiles in nine diseases, including hypertension, skin cancer, atherosclerotic heart disease, hypothyroidism and calculus of gallbladder, several of which show evidence, albeit weak, for multiple distinct profiles of genetic relative risk. The predominant pattern shows genetic risk factors having the greatest relative impact on risk of early disease, with a monotonic decrease over time, at least for the majority of variants, although the magnitude and form of the decrease varies among diseases. As a consequence, for diseases where genetic relative risk decreases over age, genetic risk factors have stronger explanatory power among younger populations, compared to older ones. We show that these patterns cannot be explained by a simple model involving the presence of unobserved covariates such as environmental factors. We discuss possible models that can explain our observations and the implications for genetic risk prediction.

The genes we inherit from our parents influence our risk for almost all diseases, from cancer to severe infections. With the explosion of genomic technologies, we are now able to use an individual’s genome to make useful predictions about future disease risk. However, recent work has shown that the predictive value of genetic information varies by context, including age, sex and ethnicity. In this paper we introduce, validate and apply new statistical methods for investigating the relationship between age and the contributions of genetic risk. These methods allow us to ask questions such as whether relative risk is constant over time, precisely how relative risk changes over time and whether all genetic risk factors have similar age profiles. By applying the methods to data from the UK Biobank, a prospective study of 500,000 people, we show that there is a tendency for genetic relative risk to decline with increasing age. We consider a series of possible explanations for the observation and conclude that there must be processes acting that we are currently unaware of, such as distinct phases of life in which genetic risk manifests itself, or interactions between genes and the environment.

Genetically determined NLRP3 inflammasome activation associates with systemic inflammation and cardiovascular mortality

AIMS

Inflammation plays an important role in cardiovascular disease (CVD) development. The NOD-like receptor protein-3 (NLRP3) inflammasome contributes to the development of atherosclerosis in animal models. Components of the NLRP3 inflammasome pathway such as interleukin-1β can therapeutically be targeted. Associations of genetically determined inflammasome-mediated systemic inflammation with CVD and mortality in humans are unknown.

METHODS AND RESULTS

We explored the association of genetic NLRP3 variants with prevalent CVD and cardiovascular mortality in 538 167 subjects on the individual participant level in an explorative gene-centric approach without performing multiple testing. Functional relevance of single-nucleotide polymorphisms on NLRP3 inflammasome activation has been evaluated in monocyte-enriched peripheral blood mononuclear cells (PBMCs). Genetic analyses identified the highly prevalent (minor allele frequency 39.9%) intronic NLRP3 variant rs10754555 to affect NLRP3 gene expression. rs10754555 carriers showed significantly higher C-reactive protein and serum amyloid A plasma levels. Carriers of the G allele showed higher NLRP3 inflammasome activation in isolated human PBMCs. In carriers of the rs10754555 variant, the prevalence of coronary artery disease was significantly higher as compared to non-carriers with a significant interaction between rs10754555 and age. Importantly, rs10754555 carriers had significantly higher risk for cardiovascular mortality during follow-up. Inflammasome inducers (e.g. urate, triglycerides, apolipoprotein C3) modulated the association between rs10754555 and mortality.

CONCLUSION

The NLRP3 intronic variant rs10754555 is associated with increased systemic inflammation, inflammasome activation, prevalent coronary artery disease, and mortality. This study provides evidence for a substantial role of genetically driven systemic inflammation in CVD and highlights the NLRP3 inflammasome as a therapeutic target.

Epigenome-wide gene-age interaction analysis reveals reversed effects of PRODH DNA methylation on survival between young and elderly early-stage NSCLC patients

DNA methylation changes during aging, but it remains unclear whether the effect of DNA methylation on lung cancer survival varies with age. Such an effect could decrease prediction accuracy and treatment efficacy. We performed a methylation–age interaction analysis using 1,230 early-stage lung adenocarcinoma patients from five cohorts. A Cox proportional hazards model was used to investigate lung adenocarcinoma and squamous cell carcinoma patients for methylation–age interactions, which were further confirmed in a validation phase. We identified one adenocarcinoma-specific CpG probe, cg14326354_PRODH, with effects significantly modified by age (HR_interaction = 0.989; 95% CI: 0.986–0.994; P = 9.18×10–7). The effect of low methylation was reversed for young and elderly patients categorized by the boundary of 95% CI standard (HR_young = 2.44; 95% CI: 1.26–4.72; P = 8.34×10-3; HR_elderly = 0.58; 95% CI: 0.42–0.82; P = 1.67×10-3). Moreover, there was an antagonistic interaction between low cg14326354_PRODH methylation and elderly age (HR_interaction = 0.21; 95% CI: 0.11–0.40; P = 2.20×10−6). In summary, low methylation of cg14326354PRODH might benefit survival of elderly lung adenocarcinoma patients, providing new insight to age-specific prediction and potential drug targeting.

Vascular ageing in hypertension: Focus on mitochondria

Hypertension is a common age-related disease, along with vascular and neurodegenerative diseases. Vascular ageing increases during hypertension, but hypertension itself accelerates vascular ageing, thus creating a vicious circle. Vascular stiffening, endothelial dysfunction, impaired contractility and vasorelaxation are the main alterations related to vascular ageing, as a consequence of vascular smooth muscle and endothelial cells senescence. Several molecular mechanisms have been involved into the functional and morphological changes of the aged vessels. Among them, oxidative stress, inflammation, extracellular matrix deregulation and mitochondrial dysfunction are the best characterized. In the present review, we discuss relevant literature about the biology of vascular and cerebrovascular ageing with a particular focus on mitochondria signalling. We underline the therapeutic strategies, able to improve mitochondrial health, which may represent a promising tool to decrease vascular dysfunction associated with ageing and hypertension-related complications.

Gene-environment interactions related to blood pressure traits in two community-based Korean cohorts

Hypertension is a complex disorder caused by genetic and environmental risk factors. Recently, genome-wide association studies (GWASs) identified more than 100 genetic variants for blood pressure traits and hypertension. However, the interactions between these genetic variants and environmental factors have not been systematically investigated. Therefore, we examined the interaction between genetic and environmental risk factors in blood pressure traits using the genetic risk score (GRS). Two Korean community-based cohorts, Cohort I (KARE; N = 8,840) and Cohort II (CAVAS; N = 9,599), were used for this study, and GRSs were calculated from 42 GWAS single-nucleotide polymorphisms (SNPs) that were validated for their association in these cohorts. We calculated GRSs in both ways by considering the effect sizes of each SNP (weighted GRS) and not considering the effect sizes (unweighted GRS). The unweighted GRS was strongly associated with systolic blood pressure, diastolic blood pressure, and hypertension (p = 9.03 × 10 ^-47 , p = 9.41 × 10 ^-48 , and p = 3.22 × 10 ^-55 by meta-analysis, respectively) and the weighted GRS showed the similar results. The environmental factors of body mass index, waist circumference, and drinking status were significantly associated with blood pressure traits, and the interaction between these factors and GRSs were examined. However, no interactions were found with either the GRS or the individual SNPs considered for the GRS. Our findings show that it is challenging to find GRS-environment interactions regarding blood pressure traits.

Interpretation and Potential Biases of Mendelian Randomization Estimates With Time-Varying Exposures

Mendelian randomization (MR) is used to answer a variety of epidemiologic questions. One stated advantage of MR is that it estimates a "lifetime effect" of exposure, though this term remains vaguely defined. Instrumental variable analysis, on which MR is based, has focused on estimating the effects of point or time-fixed exposures rather than "lifetime effects." Here we use an empirical example with data from the Rotterdam Study (Rotterdam, the Netherlands, 2009-2013) to demonstrate how confusion can arise when estimating "lifetime effects." We provide one possible definition of a lifetime effect: the average change in outcome measured at time t when the entire exposure trajectory from conception to time t is shifted by 1 unit. We show that MR only estimates this type of lifetime effect under specific conditions-for example, when the effect of the genetic variants used on exposure does not change over time. Lastly, we simulate the magnitude of bias that would result in realistic scenarios that use genetic variants with effects that change over time. We recommend that investigators in future MR studies carefully consider the effect of interest and how genetic variants whose effects change with time may impact the interpretability and validity of their results.

Methods to evaluate rare variants gene-age interaction for triglycerides

Triglycerides are an important measure of heart health. Although more than 90 genes have been found to be associated to lipids, they only explain 12 to 15% of the variance in lipid levels. Evidence suggests that age may interact with the genetic effect on lipid levels. Existing methods to detect the main effect of rare variants cannot be readily applied for testing the gene environment interaction effect of rare variants, as those methods either have unstable results or inflated Type I error rates when the main effect exists. To overcome these difficulties, we developed two statistical methods: testing of optimally weighted combination of single-nucleotide polymorphism (SNP) environment interaction (TOW-SE) and a variable weight TOW-SE (VW-TOW-SE) to test the gene environment interaction effect of rare variants by grouping SNPs into biologically meaningful SNP-sets (SNPs in a gene or pathway) to improve power and interpretability. The proposed methods can be applied to either continuous or binary environmental variables, and to either continuous or binary outcomes. Simulation studies show that Type I error rates of the proposed methods are under control. Comparing the two methods with the existing interaction sequence kernel association test (iSKAT), the VW-TOW-SE is the most powerful test and the TOW-SE is the second most powerful test when gene environment interaction effect exists for both rare and common variants. The three tests were applied to the GAW20 simulated data, among the five regions in which the main effect of common SNPs was simulated and the gene–age interaction effect was not included. As expected, none of the tests indicated positive results.

Applicability of Precision Medicine Approaches to Managing Hypertension in Rural Populations

As part of the Heart Healthy Lenoir Project, we developed a practice level intervention to improve blood pressure control. The goal of this study was: (i) to determine if single nucleotide polymorphisms (SNPs) that associate with blood pressure variation, identified in large studies, are applicable to blood pressure control in subjects from a rural population; (ii) to measure the association of these SNPs with subjects' responsiveness to the hypertension intervention; and (iii) to identify other SNPs that may help understand patient-specific responses to an intervention. We used a combination of candidate SNPs and genome-wide analyses to test associations with either baseline systolic blood pressure (SBP) or change in systolic blood pressure one year after the intervention in two genetically defined ancestral groups: African Americans (AA) and Caucasian Americans (CAU). Of the 48 candidate SNPs, 13 SNPs associated with baseline SBP in our study; however, one candidate SNP, rs592582, also associated with a change in SBP after one year. Using our study data, we identified 4 and 15 additional loci that associated with a change in SBP in the AA and CAU groups, respectively. Our analysis of gene-age interactions identified genotypes associated with SBP improvement within different age groups of our populations. Moreover, our integrative analysis identified AQP4-AS1 and PADI2 as genes whose expression levels may contribute to the pleiotropy of complex traits involved in cardiovascular health and blood pressure regulation in response to an intervention targeting hypertension. In conclusion, the identification of SNPs associated with the success of a hypertension treatment intervention suggests that genetic factors in combination with age may contribute to an individual's success in lowering SBP. If these findings prove to be applicable to other populations, the use of this genetic variation in making patient-specific interventions may help providers with making decisions to improve patient outcomes. Further investigation is required to determine the role of this genetic variance with respect to the management of hypertension such that more precise treatment recommendations may be made in the future as part of personalized medicine.

Whole exome sequence-based association analyses of plasma amyloid-β in African and European Americans; the Atherosclerosis Risk in Communities-Neurocognitive Study

Objective

We performed single-variant and gene-based association analyses of plasma amyloid-β (aβ) concentrations using whole exome sequence from 1,414 African and European Americans. Our goal was to identify genes that influence plasma aβ₄₂ concentrations and aβ₄₂:aβ₄₀ ratios in late middle age (mean = 59 years), old age (mean = 77 years), or change over time (mean = 18 years).

Methods

Plasma aβ measures were linearly regressed onto age, gender, APOE ε4 carrier status, and time elapsed between visits (fold-changes only) separately by race. Following inverse normal transformation of the residuals, seqMeta was used to conduct race-specific single-variant and gene-based association tests while adjusting for population structure. Linear regression models were fit on autosomal variants with minor allele frequencies (MAF)≥1%. T5 burden and Sequence Kernel Association (SKAT) gene-based tests assessed functional variants with MAF≤5%. Cross-race fixed effects meta-analyses were Bonferroni-corrected for the number of variants or genes tested.

Results

Seven genes were associated with aβ in late middle age or change over time; no associations were identified in old age. Single variants in KLKB1 (rs3733402; p = 4.33x10^-10) and F12 (rs1801020; p = 3.89x10^-8) were significantly associated with midlife aβ₄₂ levels through cross-race meta-analysis; the KLKB1 variant replicated internally using 1,014 additional participants with exome chip. ITPRIP, PLIN2, and TSPAN18 were associated with the midlife aβ₄₂:aβ₄₀ ratio via the T5 test; TSPAN18 was significant via the cross-race meta-analysis, whereas ITPRIP and PLIN2 were European American-specific. NCOA1 and NT5C3B were associated with the midlife aβ₄₂:aβ₄₀ ratio and the fold-change in aβ₄₂, respectively, via SKAT in African Americans. No associations replicated externally (N = 725).

Conclusion

We discovered age-dependent genetic effects, established associations between vascular-related genes (KLKB1, F12, PLIN2) and midlife plasma aβ levels, and identified a plausible Alzheimer’s Disease candidate gene (ITPRIP) influencing cell death. Plasma aβ concentrations may have dynamic biological determinants across the lifespan; plasma aβ study designs or analyses must consider age.

Rare variants in fox-1 homolog A (RBFOX1) are associated with lower blood pressure

Many large genome-wide association studies (GWAS) have identified common blood pressure (BP) variants. However, most of the identified BP variants do not overlap with the linkage evidence observed from family studies. We thus hypothesize that multiple rare variants contribute to the observed linkage evidence. We performed linkage analysis using 517 individuals in 130 European families from the Cleveland Family Study (CFS) who have been genotyped on the Illumina OmniExpress Exome array. The largest linkage peak was observed on chromosome 16p13 (MLOD = 2.81) for systolic blood pressure (SBP). Follow-up conditional linkage and association analyses in the linkage region identified multiple rare, coding variants in RBFOX1 associated with reduced SBP. In a 17-member CFS family, carriers of the missense variant rs149974858 are normotensive despite being obese (average BMI = 60 kg/m2). Gene-based association test of rare variants using SKAT-O showed significant association with SBP (p-value = 0.00403) and DBP (p-value = 0.0258) in the CFS participants and the association was replicated in large independent replication studies (N = 57,234, p-value = 0.013 for SBP, 0.0023 for PP). RBFOX1 is expressed in brain tissues, the atrial appendage and left ventricle in the heart, and in skeletal muscle tissues, organs/tissues which are potentially related to blood pressure. Our study showed that associations of rare variants could be efficiently detected using family information.

Three Approaches to Modeling Gene-Environment Interactions in Longitudinal Family Data: Gene-Smoking Interactions in Blood Pressure

Blood pressure (BP) has been shown to be substantially heritable, yet identified genetic variants explain only a small fraction of the heritability. Gene-smoking interactions have detected novel BP loci in cross-sectional family data. Longitudinal family data are available and have additional promise to identify BP loci. However, this type of data presents unique analysis challenges. Although several methods for analyzing longitudinal family data are available, which method is the most appropriate and under what conditions has not been fully studied. Using data from three clinic visits from the Framingham Heart Study, we performed association analysis accounting for gene-smoking interactions in BP at 31,203 markers on chromosome 22. We evaluated three different modeling frameworks: generalized estimating equations (GEE), hierarchical linear modeling, and pedigree-based mixed modeling. The three models performed somewhat comparably, with multiple overlaps in the most strongly associated loci from each model. Loci with the greatest significance were more strongly supported in the longitudinal analyses than in any of the component single-visit analyses. The pedigree-based mixed model was more conservative, with less inflation in the variant main effect and greater deflation in the gene-smoking interactions. The GEE, but not the other two models, resulted in substantial inflation in the tail of the distribution when variants with minor allele frequency <1% were included in the analysis. The choice of analysis method should depend on the model and the structure and complexity of the familial and longitudinal data.

Association study of NOS3 gene polymorphisms and hypertension in the Han Chinese population

BACKGROUND

Recent studies have reported that NOS3 plays an important role in cardiovascular pathology, whereas the association of NOS3 and hypertension (HT) has been controversial between African Americans and European whites. Here, we aimed to further investigate the genetic effect of unexplored loci at NOS3 on the susceptibility of HT in the Han Chinese population.

METHODS AND RESULTS

The association of three polymorphisms; rs4496877, rs1808593 and rs3918186 to HT was tested in a case control study that included 2012 HT cases and 2210 controls. Association analysis showed that there was no significant association between rs4496877, rs1808593 and rs3918186 of NOS3 and HT in the whole study population. Stratification analysis indicated that rs3918186 was significantly associated with HT in the ≥55-year-old population (OR = 1.245, 95% CI = 1.010-1.534, P = 0.04). The rs4496877 and rs1808593 were significantly associated with HT in the male population (P = 0.015) and <55-year-old population (P = 0.025), respectively (OR = 3.254, 95% CI = 1.257-8.425 and OR = 1.683, 95% CI = 1.066-2.657, respectively). Quantitative trait analysis showed that there were significant differences in systolic blood pressure (SBP) among the genotypes (AA, AT and TT) of rs3918186 in the non-intervention populations (P = 0.016). GMDR analysis showed that drinking and rs3918186 had significant interaction effects for risk of HT.

CONCLUSIONS

The findings of this study indicated that the rs4496877, rs1808593 and rs3918186 polymorphisms of NOS3 contribute to the genetic susceptibility of HT and that rs3918186 was associated with SBP in the Chinese population. Age and gender might modify the genetic effect of NOS3 on HT, and drinking significantly interacts with rs3918186.

Influence of Smoking Status and Intensity on Discovery of Blood Pressure Loci Through Gene-Smoking Interactions

BACKGROUND

Genetic variation accounts for approximately 30% of blood pressure (BP) variability but most of that variability has not been attributed to specific variants. Interactions between genes and BP-associated factors may explain some "missing heritability." Cigarette smoking increases BP after short-term exposure and decreases BP with longer exposure. Gene-smoking interactions have discovered novel BP loci, but the contribution of smoking status and intensity to gene discovery is unknown.

METHODS

We analyzed gene-smoking intensity interactions for association with systolic BP (SBP) in three subgroups from the Framingham Heart Study: current smokers only (N = 1,057), current and former smokers ("ever smokers," N = 3,374), and all subjects (N = 6,710). We used three smoking intensity variables defined at cutoffs of 10, 15, and 20 cigarettes per day (CPD). We evaluated the 1 degree-of-freedom (df) interaction and 2df joint test using generalized estimating equations.

RESULTS

Analysis of current smokers using a CPD cutoff of 10 produced two loci associated with SBP. The rs9399633 minor allele was associated with increased SBP (5 mmHg) in heavy smokers (CPD > 10) but decreased SBP (7 mmHg) in light smokers (CPD ≤ 10). The rs11717948 minor allele was associated with decreased SBP (8 mmHg) in light smokers but decreased SBP (2 mmHg) in heavy smokers. Across all nine analyses, 19 additional loci reached P < 1 × 10(-6).

DISCUSSION

Analysis of current smokers may have the highest power to detect gene-smoking interactions, despite the reduced sample size. Associations of loci near SASH1 and KLHL6/KLHL24 with SBP may be modulated by tobacco smoking.

Kernel Approach for Modeling Interaction Effects in Genetic Association Studies of Complex Quantitative Traits

The etiology of complex traits likely involves the effects of genetic and environmental factors, along with complicated interaction effects between them. Consequently, there has been interest in applying genetic association tests of complex traits that account for potential modification of the genetic effect in the presence of an environmental factor. One can perform such an analysis using a joint test of gene and gene-environment interaction. An optimal joint test would be one that remains powerful under a variety of models ranging from those of strong gene-environment interaction effect to those of little or no gene-environment interaction effect. To fill this demand, we have extended a kernel machine based approach for association mapping of multiple SNPs to consider joint tests of gene and gene-environment interaction. The kernel-based approach for joint testing is promising, because it incorporates linkage disequilibrium information from multiple SNPs simultaneously in analysis and permits flexible modeling of interaction effects. Using simulated data, we show that our kernel machine approach typically outperforms the traditional joint test under strong gene-environment interaction models and further outperforms the traditional main-effect association test under models of weak or no gene-environment interaction effects. We illustrate our test using genome-wide association data from the Grady Trauma Project, a cohort of highly traumatized, at-risk individuals, which has previously been investigated for interaction effects.

Single nucleotide polymorphism-single nucleotide polymorphism interactions among inflammation genes in the genetic architecture of blood pressure in the Framingham Heart Study

BACKGROUND

Hypertension is a major global health burden, but, although systolic and diastolic blood pressure (BP) each have estimated heritability of at least 30%, <3% of their variance has been attributed to particular genetic variants. Few studies have shown interactions between pairs of single nucleotide polymorphisms (SNPs) to be associated with BP. Although many studies use a Bonferroni correction for multiple testing to control type I error, thereby potentially reducing power, false discovery rate (FDR) approaches are also used in genome-wide studies. Renal ion balance genes have been associated with BP regulation, but, although inflammation has been studied in connection with BP, few studies have reported associations between inflammation genes and BP.

METHODS

We analyzed SNP-SNP interactions among 31 SNPs from genes involved in renal ion balance and 30 SNPs from genes involved in inflammation using data from the Framingham Heart Study.

RESULTS

No evidence of association was found for interactions among renal ion balance SNPs for either systolic or diastolic BP. A group of 3 interactions involving 6 inflammation genes (IKBKB-NFKBIA, IKBKE-CHUK, and ADIPOR2-RETN) showed evidence of association with diastolic BP with an FDR of 4.2%; no single interaction reached experiment-wide significance.

CONCLUSIONS

This study identified promising and biologically plausible candidates for interactions between inflammation genes that may be associated with DBP. Analysis using the FDR may allow detection of signals in the presence of modest noise (false positives) that a stringent approach based on Bonferroni-corrected P value thresholds may miss.

Gene-age interactions in blood pressure regulation: a large-scale investigation with the CHARGE, Global BPgen, and ICBP Consortia

Although age-dependent effects on blood pressure (BP) have been reported, they have not been systematically investigated in large-scale genome-wide association studies (GWASs). We leveraged the infrastructure of three well-established consortia (CHARGE, GBPgen, and ICBP) and a nonstandard approach (age stratification and metaregression) to conduct a genome-wide search of common variants with age-dependent effects on systolic (SBP), diastolic (DBP), mean arterial (MAP), and pulse (PP) pressure. In a two-staged design using 99,241 individuals of European ancestry, we identified 20 genome-wide significant (p ≤ 5 × 10(-8)) loci by using joint tests of the SNP main effect and SNP-age interaction. Nine of the significant loci demonstrated nominal evidence of age-dependent effects on BP by tests of the interactions alone. Index SNPs in the EHBP1L1 (DBP and MAP), CASZ1 (SBP and MAP), and GOSR2 (PP) loci exhibited the largest age interactions, with opposite directions of effect in the young versus the old. The changes in the genetic effects over time were small but nonnegligible (up to 1.58 mm Hg over 60 years). The EHBP1L1 locus was discovered through gene-age interactions only in whites but had DBP main effects replicated (p = 8.3 × 10(-4)) in 8,682 Asians from Singapore, indicating potential interethnic heterogeneity. A secondary analysis revealed 22 loci with evidence of age-specific effects (e.g., only in 20 to 29-year-olds). Age can be used to select samples with larger genetic effect sizes and more homogenous phenotypes, which may increase statistical power. Age-dependent effects identified through novel statistical approaches can provide insight into the biology and temporal regulation underlying BP associations.

Linkage analysis incorporating gene-age interactions identifies seven novel lipid loci: the Family Blood Pressure Program

OBJECTIVE

To detect novel loci with age-dependent effects on fasting (≥ 8 h) levels of total cholesterol, high-density lipoprotein, low-density lipoprotein, and triglycerides using 3600 African Americans, 1283 Asians, 3218 European Americans, and 2026 Mexican Americans from the Family Blood Pressure Program (FBPP).

METHODS

Within each subgroup (defined by network, race, and sex), we employed stepwise linear regression (retention p ≤ 0.05) to adjust lipid levels for age, age-squared, age-cubed, body-mass-index, current smoking status, current drinking status, field center, estrogen therapy (females only), as well as antidiabetic, antihypertensive, and antilipidemic medication use. For each trait, we pooled the standardized male and female residuals within each network and race and fit a generalized variance components model that incorporated gene-age interactions. We conducted FBPP-wide and race-specific meta-analyses by combining the p-values of each linkage marker across subgroups using a modified Fisher's method.

RESULTS

We identified seven novel loci with age-dependent effects; four total cholesterol loci from the meta-analysis of Mexican Americans (on chromosomes 2q24.1, 4q21.21, 8q22.2, and 12p11.23) and three high-density lipoprotein loci from the meta-analysis of all FBPP subgroups (on chromosomes 1p12, 14q11.2, and 21q21.1). These loci lacked significant genome-wide linkage or association evidence in the literature and had logarithm of odds (LOD) score ≥ 3 in the meta-analysis with LOD ≥ 1 in at least two network and race subgroups (exclusively of non-European descent).

CONCLUSION

Incorporating gene-age interactions into the analysis of lipids using multi-ethnic cohorts can enhance gene discovery. These interaction loci can guide the selection of families for sequencing studies of lipid-associated variants.

Body mass index modulates blood pressure heritability: the Family Blood Pressure Program

BACKGROUND

Candidate gene and twin studies suggest that interactions between body mass index (BMI) and genes contribute to the variability of blood pressure (BP). To determine whether there is evidence for gene-BMI interactions, we investigated the modulation of BP heritability by BMI using 4,153 blacks, 1,538 Asians, 4,013 whites, and 2,199 Hispanic Americans from the Family Blood Pressure Program.

METHODS

To capture the BP heritability dependence on BMI, we employed a generalized variance components model incorporating linear and Gaussian interactions between BMI and the genetic component. Within each race and network subgroup, we used the Akaike information criterion and likelihood ratio test to select the appropriate interaction function for each BP trait (systolic BP (SBP), diastolic BP (DBP), mean arterial pressure (MAP), and pulse pressure (PP)) and determine interaction significance, respectively.

RESULTS

BP heritabilities were significantly modified by BMI in the GenNet and SAPPHIRe Networks, which contained the youngest and least-obese participants, respectively. GenNet Whites had unimodal SBP, MAP, and PP heritabilities that peaked between BMI values of 33 and 37kg/m(2). The SBP and MAP heritabilities in GenNet Hispanic Americans, as well as the PP heritability in GenNet blacks, were increasing functions of BMI. The DBP and SBP heritabilities in the SAPPHIRe Chinese and Japanese, respectively, were decreasing functions of BMI.

CONCLUSIONS

BP heritability differed by BMI in the youngest and least-obese networks, although the shape of this dependence differed by race. Use of nonlinear gene-BMI interactions may enhance BP gene discovery efforts in individuals of European ancestry.

Gene-education interactions identify novel blood pressure loci in the Framingham Heart Study

BACKGROUND

Blood pressure (BP) variability has a genetic component, most of which has yet to be attributed to specific variants. One promising strategy for gene discovery is analysis of interactions between single-nucleotide polymorphisms (SNPs) and BP-related factors, including age, sex, and body mass index (BMI). Educational attainment, a marker for socioeconomic status, has effects on both BP and BMI.

METHODS

We investigated SNP-education interaction effects on BP in genome-wide data on 3,836 subjects in families from the Framingham Heart Study. The ABEL suite was used to adjust for age, sex, BMI, medication use, and kinship and to perform 1 degree-of-freedrom (df) and 2 df SNP-education interaction tests.

RESULTS

An SNP in PTN was associated with increased systolic BP (5.4mm Hg per minor allele) in those without a bachelor's degree but decreased systolic BP (1.6mm Hg per allele) in those with a bachelor's degree (2 df; P = 2.08 × 10(-8)). An SNP in TOX2 was associated with increased diastolic BP (DBP; 4.1mm Hg per minor allele) in those with no more educational attainment than high school but decreased DBP in those with education past high school (-0.7; 1 df; P = 3.74 × 10(-8)). Three suggestive associations were also found: in MYO16 (pulse pressure: 2 df; P = 2.89 × 10(-7)), in HAS2 (DBP: 1 df; P = 1.41 × 10(-7)), and in DLEU2 (DBP: 2 df; P = 1.93 × 10(-7)). All 5 genes are related to BP, including roles in vasodilation and angiogenesis for PTN and TOX2.

CONCLUSIONS

PTN and TOX2 are associated with BP. Analyzing SNP-education interactions may detect novel associations. Education may be a surrogate for unmeasured exposures and behaviors modifying SNP effects on BP.

Blood pressure regulation via the epithelial sodium channel: from gene to kidney and beyond

The epithelial sodium channel (ENaC) has long been recognized as playing a vital role in blood pressure (BP) regulation due to its involvement in fluid balance. The genes encoding the three ENaC subunits are likewise important contributors to hypertension, both in rare monogenic diseases and in the general population. The unusually high numbers of genetic variants associated with complex traits, including BP, that are located in non-coding areas suggest an involvement of these variants in regulatory functions. This may involve differential regulation of expression in different tissues. Emerging evidence indicates that the ENaC plays an important role in BP determination not only via its actions in the kidney, but also in other tissues commonly involved in BP regulation. The ENaC in the central nervous system is proposed to regulate BP via sympathetic nervous system activity. Recent evidence suggests that the ENaC contributes to vascular function and the myogenic response. Additional roles potentially include initiation of the baroreceptor reflex via ENaC in the baroreceptors and driving high salt intake with a 'taste for salt' via ENaC in the tongue. The present review describes the involvement of the ENaC in the determination of BP at a genetic and physiological level, detailing recent evidence for its role in the kidney and in other pertinent tissues.

Novel findings and future directions on the genetics of hypertension

PURPOSE OF REVIEW

Modern molecular techniques are identifying pathways and genes involved in the pathogenesis of the complex disorder essential hypertension. This review provides an overview of genetic methodologies and recent results in the study of high blood pressure (BP), hypertension-attributed nephropathy, and related intermediate phenotypes.

RECENT FINDINGS

Candidate gene studies have implicated aberrations in ion channels, ion channel regulation, aldosterone signaling, vasoconstriction and inflammation in essential hypertension; genome-wide association studies (GWAS) have detected more than 50 BP loci, most previously unsuspected in essential hypertension. Mapping by admixture linkage disequilibrium (MALD; or admixture mapping) recently led to a major breakthrough in hypertension-attributed kidney disease in African Americans, demonstrating the role of the apolipoprotein L1 (APOL1) and nonmuscle myosin heavy chain 9 (MYH9) genes in this primary kidney disease residing in the spectrum of focal segmental glomerulosclerosis. GWAS have detected associations between kidney function and UMOD and SHROOM3.

SUMMARY

Genetic studies confirm that 'essential hypertension' consists of disparate mechanisms that ultimately lead to elevations in systemic BP. The cause of hypertension in the majority of cases remains unknown. It is anticipated that epigenetic phenomena, rare exonic mutations, and interactions with environmental factors make additional contributions.

Biogenetic mechanisms predisposing to complex phenotypes in parents may function differently in their children

This study focuses on the participants of the Long Life Family Study to elucidate whether biogenetic mechanisms underlying relationships among heritable complex phenotypes in parents function in the same way for the same phenotypes in their children. Our results reveal 3 characteristic groups of relationships among phenotypes in parents and children. One group composed of 3 pairs of phenotypes confirms that associations among some phenotypes can be explained by the same biogenetic mechanisms working in parents and children. Two other groups including 9 phenotype pairs show that this is not a common rule. Our findings suggest that biogenetic mechanisms underlying relationships among different phenotypes, even if they are causally related, can function differently in successive generations or in different age groups of biologically related individuals. The results suggest that the role of aging-related processes in changing environment may be conceptually underestimated in current genetic association studies using genome wide resources.

Genome-wide linkage and positional association study of blood pressure response to dietary sodium intervention: the GenSalt Study

The authors conducted a genome-wide linkage scan and positional association analysis to identify the genetic determinants of salt sensitivity of blood pressure (BP) in a large family-based, dietary-feeding study. The dietary intervention was conducted among 1,906 participants in rural China (2003-2005). A 7-day low-sodium intervention was followed by a 7-day high-sodium intervention. Salt sensitivity was defined as BP responses to low- and high-sodium interventions. Signals of the logarithm of the odds to the base 10 (LOD ≥ 3) were detected at 33-42 centimorgans of chromosome 2 (2p24.3-2p24.1), with a maximum LOD score of 3.33 for diastolic blood pressure responses to high-sodium intervention. LOD scores were 2.35-2.91 for mean arterial pressure (MAP) and 0.80-1.49 for systolic blood pressure responses in this region, respectively. Correcting for multiple tests, single nucleotide polymorphism (SNP) rs11674786 (2.7 kilobases upstream of the family with sequence similarity 84, member A, gene (FAM84A)) in the linkage region was significantly associated with diastolic blood pressure (P = 0.0007) and MAP responses (P = 0.0007), and SNP rs16983422 (2.8 kilobases upstream of the visinin-like 1 gene (VSNL1)) was marginally associated with diastolic blood pressure (P = 0.005) and MAP responses (P = 0.005). An additive interaction between SNPs rs11674786 and rs16983422 was observed, with P = 7.00 × 10(-5) and P = 7.23 × 10(-5) for diastolic blood pressure and MAP responses, respectively. The authors concluded that genetic region 2p24.3-2p24.1 might harbor functional variants for the salt sensitivity of BP.

Association of leptin receptor gene polymorphisms and essential hypertension in a Chinese population

BACKGROUND

The leptin receptor (LEPR) is an important regulator of leptin activity and resistance. Several single nucleotide polymorphisms (SNP) of LEPR have been linked to diseases accompanying obesity and/or obesity-related diseases in different populations. However, the results from published studies remain inconsistent rather than conclusive.

AIM

To investigate whether LEPR SNP are associated with essential hypertension and related metabolic traits in Chinese subjects.

MATERIALS AND METHODS

A total of 544 Chinese patients with hypertension and 357 non-hypertensive subjects were screened. The genotypes of LEPR polymorphisms were determined by PCR-restriction fragment length polymorphism methods. Demographic and biochemical characteristics including waist circumference, waist-to-hip ratio, body mass index (BMI), lipids profiles, glucose metabolism, and leptin levels were obtained for analysis.

RESULTS

This case-control study showed associations between the frequencies of AA genotype and A allele of Gln223Arg and hypertension (p=0.029, p=0.002, respectively). Furthermore, the Gln223Arg polymorphism was significantly associated with plasma leptin levels (p<0.001), while no correlations between Lys109Arg SNP and hypertension were found. Multivariate logistic regression analysis evidenced that A allele carriers of Gln223Arg (AA+AG) showed higher risks of hypertension than GG carriers after adjustment of age and sex (adjusted odds ratio: 1.549, 95% confidence interval: 1.031- 2.036, p=0.035). BMI, fasting serum insulin, oral glucose tolernace test (OGTT)-2h glucose, serum leptin, as well as LDL-cholesterol (LDL-C) levels were also independent risk factors of hypertension in this population. In addition, significant associations were observed between the Gln223Arg and Lys109Arg SNP and serum total cholesterol, LDL-C, and fasting plasma glucose levels in hypertensive patients. Besides, A allele of Gln223Arg had raised diastolic blood pressure, compared with GG carriers (p=0.001). While variance of Lys109Arg was associated with waist-to-hip ratio, OGTT-2h glucose, and homeostasis model assessment of insulin resistance (p<0.05).

CONCLUSIONS

LEPR polymorphisms may be a marker for susceptibility to essential hypertension in Chinese subjects, and be involved in the development of several features including dyslipidemia and impaired glucose regulation in hypertension subjects.

Influence of age on the association of GIRK4 with metabolic syndrome

BACKGROUND

G protein-coupled inward rectifier K+ channel 4 (GIRK4) gene expressions have been implicated in the development of obesity, a key feature of metabolic syndrome (MetS). We investigated whether sequence variants of GIRK4 may represent metabolic risk factors for the Uygur Chinese population.

METHODS

The entire GIRK4 gene, including all exons, the promoter and untranslated regions from 48 MetS individuals, was studied in order to identify genetic variations associated with the disorder. Targeted genotyping of four common single nucleotide polymorphisms (SNPs: rs11221497, rs6590357, rs4937391 and rs2604204) and one novel missense mutation (M210I) was performed using the TaqMan polymerase chain reaction method for 443 MetS and 786 non-MetS subjects.

RESULTS

When all MetS cases were compared against all non-MetS controls, no significant association was found between the three SNPs (rs2604204, rs4937391 and rs6590357) and MetS status or metabolic traits. After adjustment, rs11221497 was associated with MetS (odds ratio (OR) [95% CI]=0.731 [0.551-0.968], P=0.029). Interestingly, when the MetS group was stratified into subclasses by age, an association was found for the three SNPs (rs2604204, rs4937391 and rs6590357) having estimated false discovery rates<0.001 and age of <50 y. After adjustment, the SNPs rs2604204, rs4937391 and rs6590357 were also associated with MetS in younger subjects: ORs [95% CI]: 1.678 [1.149-2.450], 1.839 [1.204-2.809] and 0.602 [0.379-0.958], respectively. All of the four SNPs showed a trend towards lower or higher metabolic traits (P<0.05) in younger subjects. In addition, a newly identified missense mutation (M210I) was not specifically related with MetS.

CONCLUSIONS

GIRK4 sequence variants appear to associate with MetS in the Uygurian population, and this association may be influenced by age.

Between candidate genes and whole genomes: time for alternative approaches in blood pressure genetics

Blood pressure has a significant genetic component, but less than 3% of the observed variance has been attributed to genetic variants identified to date. Candidate gene studies of rare, monogenic hypertensive syndromes have conclusively implicated several genes altering renal sodium balance, and studies of essential hypertension have inconsistently implicated over 50 genes in pathways affecting renal sodium balance and other functions. Genome-wide linkage scans have replicated numerous quantitative trait loci throughout the genome, and over 50 single nucleotide polymorphisms (SNPs) have been replicated in multiple genome-wide association studies. These studies provide considerable evidence that epistasis and other interactions play a role in the genetic architecture of blood pressure regulation, but candidate gene studies have limited scope to test for epistasis, and genome-wide studies have low power for both main effects and interactions. This review summarizes the genetic findings to date for blood pressure, and it proposes focused, pathway-based approaches involving epistasis, gene-environment interactions, and next-generation sequencing to further the genetic dissection of blood pressure and hypertension.

Genetic modifiers of cardiovascular phenotype caused by elastin haploinsufficiency act by extrinsic noncomplementation

Elastin haploinsufficiency causes the cardiovascular complications associated with Williams-Beuren syndrome and isolated supravalvular aortic stenosis. Significant variability exists in the vascular pathology in these individuals. Using the Eln(+/-) mouse, we sought to identify the source of this variability. Following outcrossing of C57Bl/6J Eln(+/-), two backgrounds were identified whose cardiovascular parameters deviated significantly from the parental strain. F1 progeny of the C57Bl/6J; Eln(+/-)x129X1/SvJ were more hypertensive and their arteries less compliant. In contrast, Eln(+/-) animals crossed to DBA/2J were protected from the pathologic changes associated with elastin insufficiency. Among the crosses, aortic elastin and collagen content did not correlate with quantitative vasculopathy traits. Quantitative trait locus analysis performed on F2 C57; Eln(+/-)x129 intercrosses identified highly significant peaks on chromosome 1 (LOD 9.7) for systolic blood pressure and on chromosome 9 (LOD 8.7) for aortic diameter. Additional peaks were identified that affect only Eln(+/-), including a region upstream of Eln on chromosome 5 (LOD 4.5). Bioinformatic analysis of the quantitative trait locus peaks revealed several interesting candidates, including Ren1, Ncf1, and Nos1; genes whose functions are unrelated to elastic fiber assembly, but whose effects may synergize with elastin insufficiency to predispose to hypertension and stiffer blood vessels. Real time RT-PCR studies show background-specific increased expression of Ncf1 (a subunit of the NOX2 NAPDH oxidase) that parallel the presence of increased oxidative stress in Eln(+/-) aortas. This finding raises the possibility that polymorphisms in genes affecting the generation of reactive oxygen species alter cardiovascular function in individuals with elastin haploinsufficiency through extrinsic noncomplementation.

Age-dependent association of the polymorphisms in the mitochondria-shaping gene, OPA1, with blood pressure and hypertension in Korean population

BACKGROUND

Essential hypertension is associated with mitochondrial dysfunction. Because mitochondrial dynamics; mitochondrial morphological changes are closely linked with various mitochondrial functions, we aimed to examine whether the genetic variation of the mitochondria-shaping genes influenced the susceptibility to blood pressure (BP) and hypertension.

METHODS

The quantitative BP trait analysis and hypertension case-control analysis for the total 52 single-nucleotide polymorphisms (SNPs) in the five major mitochondria-shaping genes were performed in the Korean Association Resource (KARE) study cohort (8,512 subjects).

RESULTS

In the total subjects of the KARE study cohort, there were no statistically significant associations of the SNPs in the five mitochondria-shaping genes with BP or hypertension after adjusting for multiple tests. However, the age group analysis in the 40s, 50s, and 60s age subgroups revealed that 15 SNPs out of 26 SNPs genotyped in the OPA1 gene were significantly associated with BP and/or hypertension in the 60s age subgroup and their association P values satisfied the Bonferroni-corrected significance level (P < 0.00625). Noticeably, nine SNPs were consistently associated with all the three traits; systolic BP (SBP), diastolic BP (DBP), and hypertension. In silico lookup of the associated SNPs in the Southern German population did not reveal associations with BP traits.

CONCLUSIONS

Our results indicate that genetic variation of the mitochondrial fusion-regulating gene, OPA1, might be associated with BP and hypertension in an age-dependent and population-specific manner in the Korean study cohort, and suggest that altered mitochondrial dynamics, especially involved in the mitochondrial fusion event, may play an important role in the pathogenesis of hypertension.

Association between the angiotensinogen gene T174M polymorphism and hypertension risk in the Chinese population: a meta-analysis

No consensus has been reached on the association between the angiotensinogen gene polymorphism T174M and hypertension risk in the Chinese population. We conducted a meta-analysis to systematically pursue their possible association. Case-control studies in the Chinese and English publications were identified by searching the MEDLINE, EMBASE, CBM, CNKI, Wanfang and VIP databases. The fixed-effects model and the random-effects model were applied for dichotomous outcomes to combine the results of the individual studies. After this, we selected 16 studies that met the inclusion criteria. In total, the selected studies contributed a study population containing 3828 hypertensive patients and 3251 normotensive controls. We found no statistical association between the T174M polymorphism and hypertension risk in all subjects, in a Han Chinese subgroup or in non-Han Chinese minorities. However, a statistically significant association was observed between the T174M polymorphism and a hypertensive group (systolic blood pressure ≥160 mm Hg and/or diastolic blood pressure ≥95 mm Hg) in the dominant genetic model (MM+MT vs. TT: P=0.03, odds ratio=1.71, 95% confidence interval 1.07-2.74, P(heterogeneity)=0.27, I(2)=24%, fixed-effects model). No evidence of publication bias was observed. More studies, especially studies stratified for different stages of hypertension, should be performed in the future to fully examine this question. Studies investigating gene-gene interactions, gene-environment interactions, as well as their mutual interactions will also be important.

Flexible estimation of covariance function by penalized spline with application to longitudinal family data

Longitudinal data are routinely collected in biomedical research studies. A natural model describing longitudinal data decomposes an individual's outcome as the sum of a population mean function and random subject-specific deviations. When parametric assumptions are too restrictive, methods modeling the population mean function and the random subject-specific functions nonparametrically are in demand. In some applications, it is desirable to estimate a covariance function of random subject-specific deviations. In this work, flexible yet computationally efficient methods are developed for a general class of semiparametric mixed effects models, where the functional forms of the population mean and the subject-specific curves are unspecified. We estimate nonparametric components of the model by penalized spline (P-spline, Biometrics 2001; 57:253-259), and reparameterize the random curve covariance function by a modified Cholesky decomposition (Biometrics 2002; 58:121-128) which allows for unconstrained estimation of a positive-semidefinite matrix. To provide smooth estimates, we penalize roughness of fitted curves and derive closed-form solutions in the maximization step of an EM algorithm. In addition, we present models and methods for longitudinal family data where subjects in a family are correlated and we decompose the covariance function into a subject-level source and observation-level source. We apply these methods to the multi-level Framingham Heart Study data to estimate age-specific heritability of systolic blood pressure nonparametrically.

Glutathione-related antioxidant defense system in elderly patients treated for hypertension

The purpose of this study was to analyze glutathione antioxidant defense system in elderly patients treated for hypertension. Studies were carried out in the blood collected from 18 hypertensive and 15 age- and sex-matched controls, all subjects age over 60. Hypertensives were on their usual antihypertensive treatment at the time of blood collection. The concentration of glutathione (GSH) in whole blood and activities of glutathione peroxidase (GPx-1), glutathione transferase (GST), and glutathione reductase (GR) in erythrocytes were measured. The data from patients and controls were compared using independent-samples t test. P value of 0.05 and less was considered statistically significant. We observed increased glutathione-related antioxidant defense in treated hypertensive elderly patients (HT) when compared with healthy controls (C). Mean GSH concentration was significantly higher in HT when compared with C: 3.1 ± 0.29 and 2.6 ± 0.25 mmol/L, respectively, P < 0.001. Mean activity of GR was significantly higher in HT group if compared with C: 83.4 ± 15.25 U/g Hb versus 64.2 ± 8.26 U/g Hb, respectively, P < 0.001. Mean activity of GST was significantly higher in HT group compared with C: 3.0 ± 0.60 mmol CDNB-GSH/mgHb/min and 2.6 ± 0.36 mmol CDNB-GSH/mgHb/min, respectively, P < 0.05. No difference in GPx activity was observed between two groups. These results show that glutathione-related antioxidant defense system was enhanced in elderly hypertensive patients treated for their conditions. This suggests important role of glutathione system in blood pressure regulation. Alterations in concentration and activity of antioxidants observed during antihypertensive medication are likely to be related to the effect of the treatment on NO bioavailability.

Evaluation of the gene-age interactions in HDL cholesterol, LDL cholesterol, and triglyceride levels: the impact of the SORT1 polymorphism on LDL cholesterol levels is age dependent

Several genes that influence HDL-C, LDL-C, and triglyceride levels have been identified. The effects of genetic polymorphisms on lipid levels may be age dependent. We replicated 17 of these previously identified associations and then used cross-sectional and longitudinal analysis to investigate age-SNP interaction effects. The rs646776 SNP at the SORT1 locus showed an age interaction that was significant in cross-sectional analyses of 1350 individuals from Utah (p = 0.0003) and in 2977 individuals from the NHLBI Family Heart Study (p = 0.007) as well as in longitudinal analysis of a subsample of 1099 individuals from the Utah cohort that had been followed for over 20 years (p = 0.0001). The rs646776 genotype-specific difference in LDL-C levels was significantly greater for younger individuals than for older individuals. These findings may help elucidate the mode of action of the SORT1 gene and impact potential therapeutic interventions targeting this pathway.

Dyslipidemia and the risk of incident hypertension in a population of community-dwelling Brazilian elderly: the Bambuí cohort study of aging

This study aimed to examine the prognostic value of lipid parameters for incident hypertension in elderly living in a community. The study included 306 (81% from total) persons aged > 60 years who were free of hypertension and of cardiovascular diseases at the baseline survey of the Bambuí Cohort Study of Aging. The cumulative incidence of hypertension over three years was 37.3%. The relative risk (RR) of incident hypertension decreased 0.92 for each unit of HDL-cholesterol (95%CI: 0.86-0.99) independent of several potential confounding factors. Individuals with HDL-cholesterol in the top tercile (> 55mg/dL) had a risk of hypertension halve that those in the bottom tercile (RR = 0.54; 95%CI: 0.33-0.90). Other lipid parameters had no significant effect on the outcome. High HDL-cholesterol showed an independent protective effect on subsequent development of hypertension in the elderly.

Genetic architecture of complex traits predisposing to nephropathy: hypertension

Blood pressure and hypertension have significant genetic underpinnings that may be age-dependent. The age-dependency, significant contributions from environmental factors such as diet and exercise, and inherent moment-to-moment variability complicate the identification of the genes contributing to the development of hypertension. Although genetic abnormalities may have moderate effects, the physiologic pathways involving these genes have redundant compensating mechanisms to bring the system back into equilibrium. This has the effect of reducing or completely masking the initial genetic defects, one of the hypothesized reasons for the small genetic effects found by the recent genome-wide association studies. This review article discusses the concept of initiators versus compensators in the context of finding genes related to hypertension development. A brief review is provided of some key genes found to be associated with hypertension, including the genes identified from the nine genome-wide association studies published to date.

Blood Pressure and Hypertension Are Associated With 7 Loci in the Japanese Population

Background— Two consortium-based genome-wide association studies have recently identified robust and significant associations of common variants with systolic and diastolic blood pressures in populations of European descent, warranting further investigation in populations of non-European descent.

Methods and Results— We examined the associations at 27 loci reported by the genome-wide association studies on Europeans in a screening panel of Japanese subjects (n=1526) and chose 11 loci showing association signals (1-tailed test in the screening, P <0.3) for an extensive replication study with a follow-up panel of 3 Japanese general-population cohorts (n ≤24 300). Significant associations were replicated for 7 loci— CASZ1 , MTHFR, ITGA9 , FGF5 , CYP17A1-CNNM2 , ATP2B1 , and CSK-ULK3 —with any or all of these 3 traits: systolic blood pressure ( P =1.4×10 −14 to 0.05), diastolic blood pressure ( P =1.9×10 −12 to 0.05), and hypertension ( P =2.0×10 −14 to 0.006; odds ratio, 1.10 to 1.29). The strongest association was observed for FGF5 . In the whole study panel, the variance ( R 2 ) for blood pressure explained by the 7 single-nucleotide polymorphism loci was calculated to be R 2 =0.003 for male and 0.006 for female participants. Stratified analysis implied the potential presence of a gene-age-sex interaction, although it did not reach a conclusive level of statistical significance after adjustment for multiple testing.

Conclusions— We have confirmed 7 loci associated with blood pressure and/or hypertension in the Japanese. These loci can guide fine-mapping efforts to pinpoint causal variants and causal genes with the integration of multiethnic results.

Assessment of a polymorphism of SDK1 with hypertension in Japanese Individuals

BACKGROUND

Hypertension is a major risk factor for cardiovascular disease. Although genetic studies have suggested that several genetic variants increase the risk for hypertension, the genes that underlie genetic susceptibility to this condition remain to be identified definitively. The purpose of the present study was to identify genetic variants that confer susceptibility to hypertension in Japanese individuals.

METHODS

A total of 5,734 Japanese individuals from two independent populations were examined: subject panel A comprised 2,066 hypertensive individuals and 824 controls; and subject panel B comprised 834 hypertensive individuals and 2,010 controls. The 150 polymorphisms examined in the present study were selected by genome-wide association studies of myocardial infarction and ischemic stroke with the use of the GeneChip Human Mapping 500K Array Set (Affymetrix).

RESULTS

The chi(2)-test revealed that 10 polymorphisms were significantly (P < 0.05) related to the prevalence of hypertension in subject panel A. To validate the relations, these polymorphisms were examined in subject panel B. The A-->G polymorphism (rs645106) of SDK1 and the C-->G polymorphism (rs12078839) of RABGAP1L were significantly associated with hypertension in subject panel B. Multivariable logistic regression analysis with adjustment for covariates, as well as a stepwise forward selection procedure revealed that the A-->G polymorphism of SDK1 was significantly associated with hypertension in both subject panels A and B, with the G allele protecting against this condition.

CONCLUSIONS

SDK1 may be a susceptibility gene for hypertension in Japanese individuals, although the functional relevance of the identified polymorphism was not determined.

Strategies to improve detection of hypertension genes

Multiple factors contribute to the development of hypertension, including genetic factors and environmental exposures. Various pathophysiological mechanisms are at play in the pathogenesis of hypertension and this pathogenesis, by necessity, exhibits substantial variation at the level of the individual, as it depends on the relative contribution of inherited genes and individual lifetime environmental exposures. Over time, long-term compensatory mechanisms, including responses to either chronic hypertension or to therapeutic intervention, can only obscure the initiating mechanisms of disease. Acute compensating mechanisms can also mask initiating gene effects during or after an intervention, so that early phenotype assessments during the intervention may be more likely to detect the genetic initiators. Compensatory mechanisms, working over days, weeks or even years, will likely be variably effective in minimizing the expected blood pressure rise, making it difficult to detect genetic initiating mechanisms in cross-sectional, 'steady state', or 'in balance' studies. If the lifetime risk of hypertension indeed approaches 90%, the power to identify genetic factors can only decrease with duration of disease and treatment, and prediction of hypertension becomes of vanishing significance. With multiple factors at play, we cannot expect that all causes are mutually exclusive, but it is reasonable to assume that one of these mechanisms is predominant in the initiation of the disease in any one individual. Given the heterogeneity of essential hypertension argued above, it becomes evident that the chance of identifying genetic factors that contribute to disease development will be greatest if study subjects at highest genetic predisposition are observed during age ranges when heritability is at a maximum, using the correct phenotypes, measured in the correct tissues, during the correct time window. Genes found to be significant in such studies should be densely typed in clinical trials and large population studies to assess public health and clinical applications of the findings.

A meta-analysis of the bradykinin B2 receptor gene --58C/T polymorphism with hypertension

BACKGROUND AND OBJECTIVE

Numerous studies have attempted to associate -58C/T polymorphism of bradykinin B2 receptor gene (BDKRB2) with hypertension, whereas results were often irreproducible. We performed a meta-analysis aiming to provide a comprehensive evaluation of this polymorphism and hypertension.

METHODS

Case-control reports published in English were searched totaling four studies with six populations (823 cases and 916 controls). Random-effects model was applied irrespective of between-study heterogeneity, and study quality was assessed in duplicate.

RESULTS

Compared with -58C allele carriers, those with -58T allele had a lower yet nonsignificant risk for hypertension (OR=0.86; 95% CI: 0.68-1.09; P=0.21). Lack of significance persisted after combining those with genotypes -58TC and -58TT together (OR=0.87; 95% CI: 0.67-1.09; P=0.21) or with -58TC and -58CC together (OR=0.75; 95% CI: 0.48-1.18; P=0.22) in association with hypertension. Sensitivity analyses by race indicated that comparison of -58T versus -58C generated a protective effect for hypertension in Asians (OR=0.77; 95% CI: 0.58-1.02; P=0.07) and African-Americans (OR=0.65; 95% CI: 0.43-0.98; P=0.04), but a risk effect in Caucasians (OR=1.22; 95% CI: 0.92-1.61; P=0.17). No publication bias was observed.

CONCLUSIONS

Our results suggested that -58T allele exhibited a protective effect on hypertension in Asians and African-Americans, yet a risk effect in Caucasians.

Emilin1 gene and essential hypertension: a two-stage association study in northern Han Chinese population

Background

Elastogenesis of elastic extracellular matrix (ECM) which was recognized as a major component of blood vessels has been believed for a long time to play only a passive role in the dynamic vascular changes of typical hypertension. Emilin1 gene participated in the transcription of ECM's formation and was recognized to modulate links TGF-β maturation to blood pressure homeostasis in animal study. Recently relevant advances urge further researches to investigate the role of Emilin1 gene in regulating TGF-β signals involved in elastogenesis and vascular cell defects of essential hypertension (EH).

Methods

We designed a two-stage case-control study and selected three single nucleotide polymorphisms (SNPs), rs3754734, rs2011616 and rs2304682 from the HapMap database, which covered Emilin1 gene. Totally 2,586 subjects were recruited from the International Collaborative Study of Cardiovascular Disease in Asia (InterASIA). In stage 1, all the three SNPs of the Emilin1 gene were genotyped and tested within a subsample including 503 cases and 490 controls, significant SNPs would enter into stage 2 including 814 cases with hypertension and 779 controls and analyze on the basis of testing total 2,586 subjects.

Results

In stage 1, single locus analyses showed that SNPs rs3754734 and rs2011616 had significant association with EH (P < 0.05). In stage 2, weak association for dominant model were observed by age stratification and odds ratio (ORs) of TG+GG vs. TT of rs3754734 were 0.768 (0.584-1.009), 0.985 (0.735-1.320) and 1.346 (1.003-1.806) in < 50, 50-59 and ≥ 60 years group and ORs of GA+AA vs. GG of rs2011616 were 0.745 (0.568-0.977), 1.013 (0.758-1.353) and 1.437 (1.072-1.926) in < 50, 50-59 and ≥ 60 years group respectively. Accordingly, significant interactions were detected between genotypes of rs3754734 and rs2011616 and age for EH, and ORs were 1.758 (1.180-2.620), P = 0.006 and 1.903 (1.281-2.825), P = 0.001, respectively. Results of haplotypes analysis showed that there weren't any haplotypes associated with EH directly, but the interaction of hap2 (GA) and age-group found to be significant after being adjusted for the covariates, OR was 1.220 (1.031-1.444), P value was 0.020.

Conclusion

Our findings don't support positive association of Emilin1 gene with EH, but the interaction of age and genotype variation of rs3754734 and rs2011616 might increase the risk to hypertension.