Genetic variants in novel pathways influence blood pressure and cardiovascular disease risk

The enigma of genetics etiology of atherosclerosis in the post-GWAS era

Coronary atherosclerosis is a complex heritable trait with an enigmatic genetic etiology. Genome-wide association studies (GWAS) have successfully led to identification of over 100 different loci for susceptibility to coronary atherosclerosis. Most identified single nucleotide polymorphisms (SNP)s and genes have not been previously implicated in the pathogenesis of atherosclerosis and hence, have modest biological plausibility. The novel discoveries, however, might provide the opportunity for identification of new pathways and consequently novel preventive and therapeutic targets. A notable outcome of GWAS is relatively modest effect sizes of the associated SNPs. Collectively, the identified SNPs account for a relatively small fraction of heritability of coronary atherosclerosis, which raises the question of "missing heritability". Because GWAS test the common disease-comment variant hypothesis, a plausible explanation might be the presence of uncommon and rare variants in the genome that are untested in GWAS but that might exert large effect sizes on the risk of atherosclerosis. The latter, however, remains an empiric question pending validation through experimentation. Alternative mechanisms, such as transgenerational epigenetics including microRNAs, might in part account for the heritability of coronary atherosclerosis. Collectively, the recent findings are indicative of the etiological complexity of coronary atherosclerosis. Hence, it is expected that genetic etiology of coronary atherosclerosis will remain enigmatic in the foreseeable future.

Effect of environmental and lifestyle factors on hypertension: Shimane COHRE study

Background

In recent years there has been increasing evidence of an association between residential remoteness and hypertension (HTN); however, no study has examined the effects of residential remoteness-lifestyle associations on HTN. The objective of this study was to evaluate the effects of residential remoteness, as measured by road network distance and elevation, and lifestyle associations, including access to daily products as a measure of car use, on HTN in a rural region in Japan.

Method

This is a cross-sectional population based study. We analyzed data from the Shimane COHRE study conducted from 2006 to 2009 in the rural mountainous regions of Japan. After excluding missing data, we conducted a logistic regression analysis of the data for 1,348 individuals and examined the effects of residential remoteness and lifestyle associations, including road network distance, elevation and access to daily products as a measure of car use, on the prevalence of HTN.

Principal Findings

In participants without access to car use, the odds ratios for self-reported HTN (i.e. taking antihypertensive medication) were significantly increased in those living in moderate (odds ratio (OR): 2.21, 95% confidence interval (CI): 1.19–4.08) and far (OR: 2.55, 95% CI: 1.00–6.51) road distances, whereas there were no significant associations in participants with access to car use. There were no significant associations between elevation and HTN for participants either with or without access to car transportation.

Conclusions

Our findings show that specific residential remoteness-hypertension associations vary according to access to daily products as a measure of car use in a rural mountainous area of Japan. These results advance the understanding and importance of considering residential environment, “where people live,” in establishing health policy.

Genetic susceptibility to hypertensive renal disease

Hypertensive renal disease occurs at increased frequency among the relatives of patients with this disease compared to individuals who lack a family history of disease. This suggests a heritable risk in which genetic variation may play a role. These observations have motivated a search for genetic variation contributing to this risk in both experimental animal models and in human populations. Studies of animal models indicate the capacity of natural genetic variants to contribute to disease risk and have produced a few insights into the disease mechanism. In its current phase, human population genetic studies have sought to associate genetic variation with disease in large populations by testing genotypes at a large number of common genetic variations in the genome, expecting that common genetic variants contributing to renal disease risk will be identified. These genome-wide association studies (GWAS) have been productive and are a clear technical success; they have also identified narrowly defined loci and genes containing variation contributing to disease risk. Further extension and refinement of these GWAS are likely to extend this success. However, it is also clear that few additional variants with substantial effects accounting for the greatest part of heritability will be uncovered by GWAS. This raises an interesting biological question regarding where the remaining unaccounted heritable risk may be located. At present, much consideration is being given to this question and to the challenge of testing hypotheses that lead from the various alternative mechanisms under consideration. One result of the progress of GWAS is likely to be a renewed interest in mechanisms by which related individuals can share and transmit traits independently of Mendelian inheritance. This paper reviews the current progress in this area and considers other mechanisms by which familial aggregation of risk for renal disease may arise.

Genetic predisposition to high blood pressure associates with cardiovascular complications among patients with type 2 diabetes: two independent studies

Hypertension and type 2 diabetes (T2D) commonly coexist, and both conditions are major risk factors for cardiovascular disease (CVD). We aimed to examine the association between genetic predisposition to high blood pressure and risk of CVD in individuals with T2D. The current study included 1,005 men and 1,299 women with T2D from the Health Professionals Follow-up Study and Nurses' Health Study, of whom 732 developed CVD. A genetic predisposition score was calculated on the basis of 29 established blood pressure-associated variants. The genetic predisposition score showed consistent associations with risk of CVD in men and women. In the combined results, each additional blood pressure-increasing allele was associated with a 6% increased risk of CVD (odds ratio [OR] 1.06 [95% CI 1.03-1.10]). The OR was 1.62 (1.22-2.14) for risk of CVD comparing the extreme quartiles of the genetic predisposition score. The genetic association for CVD risk was significantly stronger in patients with T2D than that estimated in the general populations by a meta-analysis (OR per SD of genetic score 1.22 [95% CI 1.10-1.35] vs. 1.10 [1.08-1.12]; I² = 71%). Our data indicate that genetic predisposition to high blood pressure is associated with an increased risk of CVD in individuals with T2D.

Systems-level approaches reveal conservation of trans-regulated genes in the rat and genetic determinants of blood pressure in humans

AIMS

Human genome-wide association studies (GWAS) of hypertension identified only few susceptibility loci with large effect that were replicated across populations. The vast majority of genes detected by GWAS has small effect and the regulatory mechanisms through which these genetic variants cause disease remain mostly unclear. Here, we used comparative genomics between human and an established rat model of hypertension to explore the transcriptional mechanisms mediating the effect of genes identified in 15 hypertension GWAS.

METHODS AND RESULTS

Time series analysis of radiotelemetric blood pressure (BP) was performed to assess 11 parameters of BP variation in recombinant inbred strains derived from the spontaneously hypertensive rat. BP data were integrated with ∼27 000 expression quantative trait loci (eQTLs) mapped across seven tissues, detecting >8000 significant associations between eQTL genes and BP variation in the rat. We then compiled a large catalogue of human genes from GWAS of hypertension and identified a subset of 2292 rat-human orthologous genes. Expression levels for 795 (34%) of these genes correlated with BP variation across rat tissues: 51 genes were cis-regulated, whereas 459 were trans-regulated and enriched for 'calcium signalling pathway' (P = 9.6 × 10(-6)) and 'ion channel' genes (P = 3.5 × 10(-7)), which are important determinants of hypertension. We identified 158 clusters of trans-eQTLs, annotated the underlying 'master regulator' genes and found significant over-representation in the human hypertension gene set (enrichment P = 5 × 10(-4)).

CONCLUSION

We showed extensive conservation of trans-regulated genes and their master regulators between rat and human hypertension. These findings reveal that small-effect genes associated with hypertension by human GWAS are likely to exert their action through coordinate regulation of pathogenic pathways.

Pharmacogenomics of drug-metabolizing enzymes: a recent update on clinical implications and endogenous effects

Interindividual differences in drug disposition are important causes for adverse drug reactions and lack of drug response. The majority of phase I and phase II drug-metabolizing enzymes (DMEs) are polymorphic and constitute essential factors for the outcome of drug therapy. Recently, both genome-wide association (GWA) studies with a focus on drug response, as well as more targeted studies of genes encoding DMEs have revealed in-depth information and provided additional information for variation in drug metabolism and drug response, resulting in increased knowledge that aids drug development and clinical practice. In addition, an increasing number of meta-analyses have been published based on several original and often conflicting pharmacogenetic studies. Here, we review data regarding the pharmacogenomics of DMEs, with particular emphasis on novelties. We conclude that recent studies have emphasized the importance of CYP2C19 polymorphism for the effects of clopidogrel, whereas the CYP2C9 polymorphism appears to have a role in anticoagulant treatment, although inferior to VKORC1. Furthermore, the analgesic and side effects of codeine in relation to CYP2D6 polymorphism are supported and the influence of CYP2D6 genotype on breast cancer recurrence during tamoxifen treatment appears relevant as based on three large studies. The influence of CYP2D6 polymorphism on the effect of antidepressants in a clinical setting is yet without any firm evidence, and the relation between CYP2D6 ultrarapid metabolizers and suicide behavior warrants further studies. There is evidence for the influence of CYP3A5 polymorphism on tacrolimus dose, although the influence on response is less studied. Recent large GWA studies support a link between CYP1A2 polymorphism and blood pressure as well as coffee consumption, and between CYP2A6 polymorphism and cigarette consumption, which in turn appears to influence the lung cancer incidence. Regarding phase II enzyme polymorphism, the anticancer treatment with mercaptopurines and irinotecan is still considered important in relation to the polymorphism of TPMT and UGT1A1, respectively. There is a need for further clarification of the clinical importance and use of all these findings, but the recent research in the field that encompasses larger studies and a whole genome perspective, improves the possibilities be able to make firm and cost-effective recommendations for drug treatment in the future.

A nutrient-wide association study on blood pressure

BACKGROUND

A nutrient-wide approach may be useful to comprehensively test and validate associations between nutrients (derived from foods and supplements) and blood pressure (BP) in an unbiased manner.

METHODS AND RESULTS

Data from 4680 participants aged 40 to 59 years in the cross-sectional International Study of Macro/Micronutrients and Blood Pressure (INTERMAP) were stratified randomly into training and testing sets. US National Health and Nutrition Examination Survey (NHANES) four cross-sectional cohorts (1999-2000, 2001-2002, 2003-2004, 2005-2006) were used for external validation. We performed multiple linear regression analyses associating each of 82 nutrients and 3 urine electrolytes with systolic and diastolic BP in the INTERMAP training set. Significant findings were validated in the INTERMAP testing set and further in the NHANES cohorts (false discovery rate <5% in training, P<0.05 for internal and external validation). Among the validated nutrients, alcohol and urinary sodium-to-potassium ratio were directly associated with systolic BP, and dietary phosphorus, magnesium, iron, thiamin, folacin, and riboflavin were inversely associated with systolic BP. In addition, dietary folacin and riboflavin were inversely associated with diastolic BP. The absolute effect sizes in the validation data (NHANES) ranged from 0.97 mm Hg lower systolic BP (phosphorus) to 0.39 mm Hg lower systolic BP (thiamin) per 1-SD difference in nutrient variable. Inclusion of nutrient intake from supplements in addition to foods gave similar results for some nutrients, though it attenuated the associations of folacin, thiamin, and riboflavin intake with BP.

CONCLUSIONS

We identified significant inverse associations between B vitamins and BP, relationships hitherto poorly investigated. Our analyses represent a systematic unbiased approach to the evaluation and validation of nutrient-BP associations.

Hypertension susceptibility loci and blood pressure response to antihypertensives: results from the pharmacogenomic evaluation of antihypertensive responses study

BACKGROUND

To date, 39 single nucleotide polymorphisms (SNPs) have been associated with blood pressure (BP) or hypertension in genome-wide association studies in whites. Our hypothesis is that the loci/SNPs associated with BP/hypertension are also associated with BP response to antihypertensive drugs.

METHODS AND RESULTS

We assessed the association of these loci with BP response to atenolol or hydrochlorothiazide monotherapy in 768 hypertensive participants in the Pharmacogenomics Responses of Antihypertensive Responses study. Linear regression analysis was performed on whites for each SNP in an additive model adjusting for baseline BP, age, sex, and principal components for ancestry. Genetic scores were constructed to include SNPs with nominal associations, and empirical P values were determined by permutation test. Genotypes of 37 loci were obtained from Illumina 50K cardiovascular or Omni1M genome-wide association study chips. In whites, no SNPs reached Bonferroni-corrected α of 0.0014, 6 reached nominal significance (P<0.05), and 3 were associated with atenolol BP response at P<0.01. The genetic score of the atenolol BP-lowering alleles was associated with response to atenolol (P=3.3 × 10(-6) for systolic BP; P=1.6 × 10(-6) for diastolic BP). The genetic score of the hydrochlorothiazide BP-lowering alleles was associated with response to hydrochlorothiazide (P=0.0006 for systolic BP; P=0.0003 for diastolic BP). Both risk score P values were <0.01 based on the empirical distribution from the permutation test.

CONCLUSIONS

These findings suggest that selected signals from hypertension genome-wide association studies may predict BP response to atenolol and hydrochlorothiazide when assessed through risk scoring. Clinical Trial Registration Information- clinicaltrials.gov; Identifier: NCT00246519.

Effect of long-term exposure to lower low-density lipoprotein cholesterol beginning early in life on the risk of coronary heart disease: a Mendelian randomization analysis

OBJECTIVES

The purpose of this study was to estimate the effect of long-term exposure to lower plasma low-density lipoprotein cholesterol (LDL-C) on the risk of coronary heart disease (CHD).

BACKGROUND

LDL-C is causally related to the risk of CHD. However, the association between long-term exposure to lower LDL-C beginning early in life and the risk of CHD has not been reliably quantified.

METHODS

We conducted a series of meta-analyses to estimate the effect of long-term exposure to lower LDL-C on the risk of CHD mediated by 9 polymorphisms in 6 different genes. We then combined these Mendelian randomization studies in a meta-analysis to obtain a more precise estimate of the effect of long-term exposure to lower LDL-C and compared it with the clinical benefit associated with the same magnitude of LDL-C reduction during treatment with a statin.

RESULTS

All 9 polymorphisms were associated with a highly consistent reduction in the risk of CHD per unit lower LDL-C, with no evidence of heterogeneity of effect (I(2) = 0.0%). In a meta-analysis combining nonoverlapping data from 312,321 participants, naturally random allocation to long-term exposure to lower LDL-C was associated with a 54.5% (95% confidence interval: 48.8% to 59.5%) reduction in the risk of CHD for each mmol/l (38.7 mg/dl) lower LDL-C. This represents a 3-fold greater reduction in the risk of CHD per unit lower LDL-C than that observed during treatment with a statin started later in life (p = 8.43 × 10(-19)).

CONCLUSIONS

Prolonged exposure to lower LDL-C beginning early in life is associated with a substantially greater reduction in the risk of CHD than the current practice of lowering LDL-C beginning later in life.

Human genetics offers an emerging picture of common pathways and mechanisms in autoimmunity

In genetic studies of autoimmune and inflammatory diseases, one clear finding that has emerged from genome-wide association studies is that a substantial fraction of variation modifying risk in one disease also contributes mediate risk to multiple, additional autoimmune and inflammatory diseases. The unexpected magnitude of this overlap presents the unique opportunity to dissect the pathogenic mechanisms underlying multiple disease states in the expectation that this may lead to both more sensitive diagnostics and novel therapies. Here, we review the current evidence for this shared genetic architecture and, based on these data, outline models for shared pathways, the underlying hypotheses for them, how these models can be tested and validated.

Task3 potassium channel gene invalidation causes low renin and salt-sensitive arterial hypertension

Task1 and Task3 potassium channels (Task: tandem of P domains in a weak inward rectifying K(+) channel-related acid-sensitive K(+) channel) are believed to control the membrane voltage of aldosterone-producing adrenal glomerulosa cells. This study aimed at understanding the role of Task3 for the control of aldosterone secretion. The adrenal phenotype of Task3(-/-) mice was investigated using electrophysiology, adrenal slices, and blood pressure measurements. Primary adrenocortical cells of Task3(-/-) mice were strongly depolarized compared with wild-type (-52 vs. -79 mV), and in fresh adrenal slices Ca(2+) signaling of Task3(-/-) glomerulosa cells was abnormal. In living Task3(-/-) mice, the regulation of aldosterone secretion showed specific deficits: Under low Na(+) and high K(+) diets, protocols known to increase aldosterone, and under standard diet, Task3 inactivation was compensated and aldosterone was normal. However, high Na(+) and low K(+) diets, two protocols known to lower aldosterone, failed to lower aldosterone in Task3(-/-) mice. The physiological regulation of aldosterone was disturbed: aldosterone-renin ratio, an indicator of autonomous aldosterone secretion, was 3-fold elevated at standard and high Na(+) diets. Isolated adrenal glands of Task3(-/-) produced 2-fold more aldosterone. As a consequence, Task3(-/-) mice showed salt-sensitive arterial hypertension (plus 10 mm Hg). In conclusion, Task3 plays an important role in the adaptation of aldosterone secretion to dietary salt intake.

Platt versus Pickering: what molecular insight to primary hyperaldosteronism tells us about hypertension

Recent genome-wide analyses have found 50 loci associated with variation in blood pressure but failed to advance understanding of the molecular basis of hypertension. Whether hypertension is not after all due to multiple common variants or is simply an order of magnitude more complex than previously suspected remains unsettled - in part because only a minority of subjects in the analyses had true hypertension. A better starting point than normotensive subjects for explaining hypertension may be the most common distinct cause of hypertension, primary hyperaldosteronism (PHA). The findings that 40% of patients with an aldosterone-producing adenoma (APA) of the adrenal have somatic gain-of-function mutations in a single gene, KCNJ5, and that this gene is, less frequently, mutated in inherited cases of PHA, potentially transform the understanding and management of hypertension. Firstly, they illustrate how hypertension could be due to a multiplicity of uncommon variants. Mutations that present with abnormal electrolytes and anatomy are the easiest to detect but are likely the tip of the iceberg. Secondly, we found a genotype:phenotype pattern, with KCNJ5 mutations inducing larger APAs in the cortisol-secreting zona fasciculata in young women. Smaller APAs without KCNJ5 mutations usually present in older men with resistant hypertension, having been overlooked earlier because of their size. This reflects their compact zona glomerulosa cells. Routine measurement of plasma renin in hypertension and a new positron emission tomography/computerized tomography allow prompt diagnosis and management of PHA before resistant hypertension ensues. Wider recognition of distinct phenotypes should permit earlier, specific treatment and reduce life-time risk of complications.

Alanine-glyoxylate aminotransferase-2 metabolizes endogenous methylarginines, regulates NO, and controls blood pressure

OBJECTIVE

Asymmetric dimethylarginine is an endogenous inhibitor of NO synthesis that may mediate cardiovascular disease. Alanine-glyoxylate aminotransferase-2 (AGXT2) has been proposed to degrade asymmetric dimethylarginine. We investigated the significance of AGXT2 in methylarginine metabolism in vivo and examined the effect of this enzyme on blood pressure.

METHODS AND RESULTS

In isolated mouse kidney mitochondria, we show asymmetric dimethylarginine deamination under physiological conditions. We demonstrate increased asymmetric dimethylarginine, reduced NO, and hypertension in an AGXT2 knockout mouse. We provide evidence for a role of AGXT2 in methylarginine metabolism in humans by demonstrating an inverse relationship between renal (allograft) gene expression and circulating substrate levels and an association between expression and urinary concentrations of the product. Finally, we examined data from a meta-analysis of blood pressure genome-wide association studies. No genome-wide significance was observed, but taking a hypothesis-driven approach, there was a suggestive association between the T allele at rs37369 (which causes a valine-isoleucine substitution and altered levels of AGXT2 substrate) and a modest increase in diastolic blood pressure (P=0.0052).

CONCLUSIONS

Although the effect of variation at rs37369 needs further study, these findings suggest that AGXT2 is an important regulator of methylarginines and represents a novel mechanism through which the kidney regulates blood pressure.

Associations between variation in CHRNA5-CHRNA3-CHRNB4, body mass index and blood pressure in the Northern Finland Birth Cohort 1966

BACKGROUND

The CHRNA5-CHRNA3-CHRNB4 gene cluster on 15q25 has consistently been associated with smoking quantity, nicotine dependence and lung cancer. Recent research also points towards its involvement in cardiovascular homeostasis, but studies in large human samples are lacking, especially on the role of the gene cluster in blood pressure regulation.

METHODOLOGY/PRINCIPAL FINDINGS

We studied the associations between 18 single nucleotide polymorphisms (SNPs) in CHRNA5-CHRNA3-CHRNB4 and systolic blood pressure (SBP), diastolic blood pressure (DBP), and body mass index (BMI) in 5402 young adults from the Northern Finland Birth Cohort 1966. We observed some evidence for associations between two SNPs and SBP and between six SNPs and BMI; the evidence for associations with DBP was weaker. The associations with the three phenotypes were driven by different loci with low linkage disequilibrium with each other. The associations appeared more pronounced in smokers, such that the smoking-increasing alleles would predict lower SBP and BMI. Each additional copy of the rs1948 G-allele and the rs950776 A-allele reduced SBP on average by -1.21 (95% CI -2.01, -0.40) mmHg in smokers. The variants associated with BMI included rs2036534, rs6495309, rs1996371, rs6495314, rs4887077 and rs11638372 and had an average effect size of -0.38 (-0.68, -0.08) kg/m(2) per an additional copy of the risk allele in smokers. Formal assessments of interactions provided weaker support for these findings, especially after adjustment for multiple testing.

CONCLUSIONS

Variation at 15q25 appears to interact with smoking status in influencing SBP and BMI. The genetic loci associated with SBP were in low linkage disequilibrium with those associated with BMI suggesting that the gene cluster might regulate SBP through biological mechanisms that partly differ from those regulating BMI. Further studies in larger samples are needed for more precise evaluation of the possible interactions, and to understand the mechanisms behind.

Several lipid-related gene polymorphisms interact with overweight/obesity to modulate blood pressure levels

Little is known about the interactions of single nucleotide polymorphisms (SNPs) and overweight/obesity on blood pressure levels. The present study was undertaken to detect 10 lipid-related gene SNPs and their interactions with overweight/obesity on blood pressure levels. Genotyping of ATP-binding cassette transporter A1 (ABCA-1) V825I, acyl-CoA:cholesterol acyltransferase-1 (ACAT-1) rs1044925, low density lipoprotein receptor (LDL-R) AvaII hepatic lipase gene (LIPC) −250G > A, endothelial lipase gene (LIPG) 584C > T, methylenetetrahydrofolate reductase (MTHFR) 677C > T, the E3 ubiquitin ligase myosin regulatory light chain-interacting protein (MYLIP) rs3757354, proprotein convertase subtilisin-like kexin type 9 (PCSK9) E670G, peroxisome proliferator-activated receptor delta (PPARD) +294T > C, and Scavenger receptor class B type 1 (SCARB1) rs5888 was performed in 978 normal weight and 751 overweight/obese subjects. The interactions were detected by factorial regression analysis. The genotypes of ACAT-1 AC, LIPC GA and AA, and SCARB1 TT; LDL-R A-A- and LIPC GA; and SCARB1 TT were interacted with overweight/obesity to increase systolic, diastolic blood pressure (SBP, DBP) and pulse pressure (PP) levels; respectively. The genotypes of ACAT-1 CC; ACAT-1 AA and CC were interacted with overweight/obesity to decrease SBP, PP levels (p < 0.01–0.001); respectively. The differences in blood pressure levels between normal weight and overweight/obese subjects might partly result from different interactions of several SNPs and overweight/obesity.

Genetic biomarkers of hypertension and future challenges integrating epigenomics

Essential hypertension is a multifactorial disease, considered to be one of the world's greatest public health problems. Despite recent, major, technical advances aiming to elucidate its genetic component, the discovered biomarkers up to now were reported to have only small effects, explaining consequently a tiny fraction of its phenotypic variance and resulting in a large proportion of missing heritability. Likewise, little evidence is available with regard to the epigenetic regulation of essential hypertension, since no robust biomarkers have yet been reported. In the current review, we discuss the main approaches used exclusively to study the genetics and epigenetics of essential hypertension, the biomarkers identified, their clinical utility and the difficulties to be overcome. Furthermore, we propose a new category of functional genetic-epigenetic biomarkers, eMethSNPs, and we provide their hypothetical gene expression profiles for a genetic functional regulation of hypertension via DNA methylation. Though believed to be infrequent, eMethSNPs could constitute a new category of mechanistically-based genetic biomarkers predisposing to essential hypertension.

Endothelial actions of atrial and B-type natriuretic peptides

The cardiac hormone atrial natriuretic peptide (ANP) is critically involved in the maintenance of arterial blood pressure and intravascular volume homeostasis. Its cGMP-producing GC-A receptor is densely expressed in the microvascular endothelium of the lung and systemic circulation, but the functional relevance is controversial. Some studies reported that ANP stimulates endothelial cell permeability, whereas others described that the peptide attenuates endothelial barrier dysfunction provoked by inflammatory agents such as thrombin or histamine. Many studies in vitro addressed the effects of ANP on endothelial proliferation and migration. Again, both pro- and anti-angiogenic properties were described. To unravel the role of the endothelial actions of ANP in vivo, we inactivated the murine GC-A gene selectively in endothelial cells by homologous loxP/Cre-mediated recombination. Our studies in these mice indicate that ANP, via endothelial GC-A, increases endothelial albumin permeability in the microcirculation of the skin and skeletal muscle. This effect is critically involved in the endocrine hypovolaemic, hypotensive actions of the cardiac hormone. On the other hand the homologous GC-A-activating B-type NP (BNP), which is produced by cardiac myocytes and many other cell types in response to stressors such as hypoxia, possibly exerts more paracrine than endocrine actions. For instance, within the ischaemic skeletal muscle BNP released from activated satellite cells can improve the regeneration of neighbouring endothelia. This review will focus on recent advancements in our understanding of endothelial NP/GC-A signalling in the pulmonary versus systemic circulation. It will discuss possible mechanisms accounting for the discrepant observations made for the endothelial actions of this hormone-receptor system and distinguish between (patho)physiological and pharmacological actions. Lastly it will emphasize the potential therapeutical implications derived from the actions of NPs on endothelial permeability and regeneration.

Association of genetic variation in the mitochondrial genome with blood pressure and metabolic traits

Elevated blood pressure (BP) is a major risk factor for cardiovascular disease. Several studies have noted a consistent maternal effect on BP; consequently, mitochondrial DNA variation has become an additional target of investigation of the missing BP heritability. Analyses of common mitochondrial DNA polymorphisms, however, have not found evidence of association with hypertension. To explore associations of uncommon (frequency>5%) mitochon drial DNA variants with BP, we identified uncommon/rare variants through sequencing the entire mitochondrial genome in 32 unrelated individuals with extreme-high BP in the Framingham Heart Study and genotyped 40 mitochondrial single nucleotide polymorphisms in 7219 Framingham Heart Study participants. The nonsynonymous mitochondrial single nucleotide polymorphism 5913G>A (Asp4Asn) in the cytochrome c oxidase subunit 1 of respiratory complex IV demonstrated significant associations with BP and fasting blood glucose (FBG) levels. Individuals with the rare 5913A allele had, on average, 7-mm Hg higher systolic BP at baseline (Pempirical=0.05) and 17-mg/dL higher mean FBG over 25 years of follow-up (Pempirical=0.009). Significant associations with FBG levels were also detected for nonsynonymous mitochondrial single nucleotide polymorphism 3316G>A (Ala4Thr) in the NADH dehydrogenase subunit 1 of complex I. On average, individuals with rare allele 3316A had 17- and 25-mg/dL higher FBG at baseline (Pempirical=0.01) and over 25 years of follow-up (Pempirical=0.007). Our findings provide the first evidence of putative association of variants in the mitochondrial genome with systolic BP and FBG in the general population. Replication in independent samples, however, is needed to confirm these putative associations.

Genetic variants associated with adult blood pressure and kidney function do not affect fetal kidney volume. The Generation R Study

BACKGROUND

Smaller kidneys with reduced number of nephrons in early life lead to impaired kidney function and risk for hypertension and chronic kidney disease. These associations might be partly explained by common genetic variation.

AIMS

To assess the associations between common genetic variants, which have recently shown to be associated with blood pressure or kidney function, with fetal kidney volume.

STUDY DESIGN

A prospective population based cohort study in Rotterdam, The Netherlands.

SUBJECTS

855 children, followed from early fetal life onwards (born 2003-2005).

PREDICTOR

Common genetic variants previously associated with blood pressure or kidney function.

OUTCOME MEASURES

Combined third trimester fetal kidney volume.

RESULTS

After taking into account multiple testing, only rs12940887 (near ZNF652) was significantly associated with fetal kidney volume (β: 0.88 (95% CI: 0.40; 1.37) cm(3) per minor allele, P-value<0.001), but the effect showed the opposite direction as expected. The remaining common genetic variants were not associated with fetal kidney volume. We also did not find associations of genetic variants previously shown to affect newborn kidney volume, with third trimester fetal kidney volume.

CONCLUSIONS

Our results suggest that common genetic variants, associated with kidney function or disease and blood pressure, do not affect the third trimester fetal kidney volume. Further studies are needed to elucidate the mechanisms underlying the associations between small kidney size and increased risks of hypertension and impaired kidney function in adulthood.

Genetic and genomic approaches to the detection of heart transplant rejection

Since Christiaan Barnard performed the first heart transplant in 1967, over 100,000 heart transplants have been performed worldwide. As was true then, rejection remains the major threat to the function and survival of the allograft. The development of the endomyocardial biopsy as a means to monitor for rejection has allowed heart transplantation to thrive as a therapy for patients with end-stage heart disease. The need for a noninvasive method of rejection surveillance led to the development of the first genetic test for allograft rejection, the AlloMap^®. In this article, after presenting the pathological and clinical features of cardiac allograft rejection, the authors discuss the development and application of gene-expression testing for the detection of cardiac allograft rejection. We then explore emerging 'omic' approaches that will be the rejection detection methods of the future.

New susceptibility loci associated with kidney disease in type 1 diabetes

Diabetic kidney disease, or diabetic nephropathy (DN), is a major complication of diabetes and the leading cause of end-stage renal disease (ESRD) that requires dialysis treatment or kidney transplantation. In addition to the decrease in the quality of life, DN accounts for a large proportion of the excess mortality associated with type 1 diabetes (T1D). Whereas the degree of glycemia plays a pivotal role in DN, a subset of individuals with poorly controlled T1D do not develop DN. Furthermore, strong familial aggregation supports genetic susceptibility to DN. However, the genes and the molecular mechanisms behind the disease remain poorly understood, and current therapeutic strategies rarely result in reversal of DN. In the GEnetics of Nephropathy: an International Effort (GENIE) consortium, we have undertaken a meta-analysis of genome-wide association studies (GWAS) of T1D DN comprising ~2.4 million single nucleotide polymorphisms (SNPs) imputed in 6,691 individuals. After additional genotyping of 41 top ranked SNPs representing 24 independent signals in 5,873 individuals, combined meta-analysis revealed association of two SNPs with ESRD: rs7583877 in the AFF3 gene (P = 1.2 × 10(-8)) and an intergenic SNP on chromosome 15q26 between the genes RGMA and MCTP2, rs12437854 (P = 2.0 × 10(-9)). Functional data suggest that AFF3 influences renal tubule fibrosis via the transforming growth factor-beta (TGF-β1) pathway. The strongest association with DN as a primary phenotype was seen for an intronic SNP in the ERBB4 gene (rs7588550, P = 2.1 × 10(-7)), a gene with type 2 diabetes DN differential expression and in the same intron as a variant with cis-eQTL expression of ERBB4. All these detected associations represent new signals in the pathogenesis of DN.

Neutral endopeptidase inhibition and the natriuretic peptide system: an evolving strategy in cardiovascular therapeutics

Hypertension and heart failure (HF) are common diseases that, despite advances in medical therapy, continue to be associated with high morbidity and mortality. Therefore, innovative therapeutic strategies are needed. Inhibition of the neutral endopeptidase (NEPinh) had been investigated as a potential novel therapeutic approach because of its ability to increase the plasma concentrations of the natriuretic peptides (NPs). Indeed, the NPs have potent natriuretic and vasodilator properties, inhibit the activity of the renin-angiotensin-aldosterone system, lower sympathetic drive, and have antiproliferative and antihypertrophic effects. Such potentially beneficial effects can be theoretically achieved by the use of NEPinh. However, studies have shown that NEPinh alone does not result in clinically meaningful blood pressure-lowering actions. More recently, NEPinh has been used in combination with other cardiovascular agents, such as angiotensin-converting enzyme inhibitors, and antagonists of the angiotensin receptor. Another future possible combination would be the use of NEPinh with NPs or their newly developed chimeric peptides. This review summarizes the current knowledge of the use and effects of NEPinh alone or in combination with other therapeutic agents for the treatment of human cardiovascular disease such as HF and hypertension.

Pharmacogenetic implications for eight common blood pressure-associated single-nucleotide polymorphisms

OBJECTIVE

We aimed to test whether eight common recently identified single-nucleotide polymorphisms (SNPs), strongly associated with blood pressure (BP) in the population, also have impact on the degree of BP reduction by antihypertensive agents with different mechanisms.

METHODS

In 3863 Swedish hypertensive patients, we related number of unfavorable alleles of each SNP (i.e. alleles associated with higher baseline BP) to the magnitude of BP reduction during 6 months of monotherapy with either a beta-blocker, a thiazide diuretic or diltiazem.

RESULTS

For six SNPs (rs16998073, rs1378942, rs3184504, rs1530440, rs16948048, rs17367504) no pharmacogenetic interactions were suggested, whereas two SNPs showed nominal evidence of association with treatment response: PLCD3-rs12946454 associated with more SBP (beta = 1.53 mmHg per unfavorable allele; P = 0.010) and DBP (beta = 0.73 mmHg per unfavorable allele; P = 0.014) reduction in patients treated with diltiazem, in contrast to those treated with beta-blockers or diuretics wherein no treatment response association was found. CYP17A1-rs11191548 associated with less DBP reduction (beta = -1.26 mmHg per unfavorable allele; P = 0.018) in patients treated with beta-blockers or diuretics, whereas there was no treatment response association in diltiazem-treated patients. However, if accounting for multiple testing, the significant associations for rs12946454 and rs11191548 were attenuated.

CONCLUSION

For a majority of these, eight recently identified BP-associated SNPs, there are probably no important pharmacogenetic interactions for BP reduction with use of beta-blockers, diuretics or diltiazem. Whether the nominally significant associations for rs12946454 and rs11191548 are true signals and could be of possible clinical relevance for deciding treatment of polygenic essential hypertension should be further tested.

Burden of risk alleles for hypertension increases risk of intracerebral hemorrhage

BACKGROUND AND PURPOSE

Genetic variation influences risk of intracerebral hemorrhage (ICH). Hypertension (HTN) is a potent risk factor for ICH and several common genetic variants (single nucleotide polymorphisms [SNPs]) associated with blood pressure levels have been identified. We sought to determine whether the cumulative burden of blood pressure-related SNPs is associated with risk of ICH and pre-ICH diagnosis of HTN.

METHODS

We conducted a prospective multicenter case-control study in 2272 subjects of European ancestry (1025 cases and 1247 control subjects). Thirty-nine SNPs reported to be associated with blood pressure levels were identified from the National Human Genome Research Institute genomewide association study catalog. Single-SNP association analyses were performed for the outcomes ICH and pre-ICH HTN. Subsequently, weighted and unweighted genetic risk scores were constructed using these SNPs and entered as the independent variable in logistic regression models with ICH and pre-ICH HTN as the dependent variables.

RESULTS

No single SNP was associated with either ICH or pre-ICH HTN. The blood pressure-based unweighted genetic risk score was associated with risk of ICH (OR, 1.11; 95% CI, 1.02-1.21; P=0.01) and the subset of ICH in deep regions (OR, 1.18; 95% CI, 1.07-1.30; P=0.001), but not with the subset of lobar ICH. The score was associated with a history of HTN among control subjects (OR, 1.17; 95% CI, 1.04-1.31; P=0.009) and ICH cases (OR, 1.15; 95% CI, 1.01-1.31; P=0.04). Similar results were obtained when using a weighted score.

CONCLUSIONS

Increasing numbers of high blood pressure-related alleles are associated with increased risk of deep ICH as well as with clinically identified HTN.

The genetics of coronary artery disease

PURPOSE OF REVIEW

Prevention of coronary artery disease (CAD) is an appropriate goal for the 21st century. Randomized clinical studies consistently show a 30-40% reduction in mortality and morbidity by modifying known risk factors. However, genetic risk, estimated to account for 40-60% of susceptibility to CAD, has until recently been unknown. Comprehensive prevention will require knowledge of both.

RECENT FINDINGS

The 21st century technology has responded to the challenge. Whereas the first genetic risk variant was not discovered until 2007 (9p21), a total of 36 genetic risk factors for CAD have been discovered and verified in large sample sizes. A startling discovery was that over two-thirds of these factors do not act through known risk factors or mechanisms. This obviously has great implications for the pathogenesis of CAD and presents many potential targets for new therapy. These genetic risk factors occur more commonly in the population than expected, with over half of them occurring in more than 50% of the population, and 10 of them occurring in at least 75% of the population.

SUMMARY

The role of genetic risk factors in genetic screening for prevention of heart disease is yet to be defined. The technology is already available, but functional analysis may be a prerequisite for their clinical application.

Intracellular pH in the resistance vasculature: regulation and functional implications

Net acid extrusion from vascular smooth muscle (VSMCs) and endothelial cells (ECs) in the wall of resistance arteries is mediated by the Na(+),HCO(3)(-) cotransporter NBCn1 (SLC4A7) and the Na(+)/H(+) exchanger NHE1 (SLC9A1) and is essential for intracellular pH (pH(i)) control. Experimental evidence suggests that the pH(i) of VSMCs and ECs modulates both vasocontractile and vasodilatory functions in resistance arteries with implications for blood pressure regulation. The connection between disturbed pH(i) and altered cardiovascular function has been substantiated by a genome-wide association study showing a link between NBCn1 and human hypertension. On this basis, we here review the current evidence regarding (a) molecular mechanisms involved in pH(i) control in VSMCs and ECs of resistance arteries at rest and during contractions, (b) implications of disturbed pH(i) for resistance artery function, and (c) involvement of disturbed pH(i) in the pathogenesis of vascular disease. The current evidence clearly implies that pH(i) of VSMCs and ECs modulates vascular function and suggests that disturbed pH(i) either consequent to disturbed regulation or due to metabolic challenges needs to be taken into consideration as a mechanistic component of artery dysfunction and disturbed blood pressure regulation.

Genomic epidemiology of blood pressure salt sensitivity

High blood pressure (BP) is a complex trait determined by genetic and environmental factors, as well as their interactions. Over the past few decades, there has been substantial progress elucidating the genetic determinants underlying BP response to sodium intake, or BP salt sensitivity. Research of monogenic BP disorders has highlighted the importance of renal salt handling in BP regulation, implicating genes and biological pathways subsequently identified in candidate gene studies of salt sensitivity. Despite these advancements, certain candidate gene findings await replication evidence, and some biological pathways warrant further investigation. Furthermore, results from genome-wide association studies (GWASs) and sequencing work have yet to be reported. GWAS will be valuable for uncovering novel mechanisms underlying salt sensitivity, whereas future sequencing efforts promise the discovery of functional variants related to this complex trait. Delineating the genetic architecture of salt sensitivity will be critical to understanding how genes and dietary sodium interact to influence BP.

Hypertension in developing countries

Data from different national and regional surveys show that hypertension is common in developing countries, particularly in urban areas, and that rates of awareness, treatment, and control are low. Several hypertension risk factors seem to be more common in developing countries than in developed regions. Findings from serial surveys show an increasing prevalence of hypertension in developing countries, possibly caused by urbanisation, ageing of population, changes to dietary habits, and social stress. High illiteracy rates, poor access to health facilities, bad dietary habits, poverty, and high costs of drugs contribute to poor blood pressure control. The health system in many developing countries is inadequate because of low funds, poor infrastructure, and inexperience. Priority is given to acute disorders, child and maternal health care, and control of communicable diseases. Governments, together with medical societies and non-governmental organisations, should support and promote preventive programmes aiming to increase public awareness, educate physicians, and reduce salt intake. Regulations for the food industry and the production and availability of generic drugs should be reinforced.

Plasma HDL cholesterol and risk of myocardial infarction: a mendelian randomisation study

BACKGROUND

High plasma HDL cholesterol is associated with reduced risk of myocardial infarction, but whether this association is causal is unclear. Exploiting the fact that genotypes are randomly assigned at meiosis, are independent of non-genetic confounding, and are unmodified by disease processes, mendelian randomisation can be used to test the hypothesis that the association of a plasma biomarker with disease is causal.

METHODS

We performed two mendelian randomisation analyses. First, we used as an instrument a single nucleotide polymorphism (SNP) in the endothelial lipase gene (LIPG Asn396Ser) and tested this SNP in 20 studies (20,913 myocardial infarction cases, 95,407 controls). Second, we used as an instrument a genetic score consisting of 14 common SNPs that exclusively associate with HDL cholesterol and tested this score in up to 12,482 cases of myocardial infarction and 41,331 controls. As a positive control, we also tested a genetic score of 13 common SNPs exclusively associated with LDL cholesterol.

FINDINGS

Carriers of the LIPG 396Ser allele (2·6% frequency) had higher HDL cholesterol (0·14 mmol/L higher, p=8×10(-13)) but similar levels of other lipid and non-lipid risk factors for myocardial infarction compared with non-carriers. This difference in HDL cholesterol is expected to decrease risk of myocardial infarction by 13% (odds ratio [OR] 0·87, 95% CI 0·84-0·91). However, we noted that the 396Ser allele was not associated with risk of myocardial infarction (OR 0·99, 95% CI 0·88-1·11, p=0·85). From observational epidemiology, an increase of 1 SD in HDL cholesterol was associated with reduced risk of myocardial infarction (OR 0·62, 95% CI 0·58-0·66). However, a 1 SD increase in HDL cholesterol due to genetic score was not associated with risk of myocardial infarction (OR 0·93, 95% CI 0·68-1·26, p=0·63). For LDL cholesterol, the estimate from observational epidemiology (a 1 SD increase in LDL cholesterol associated with OR 1·54, 95% CI 1·45-1·63) was concordant with that from genetic score (OR 2·13, 95% CI 1·69-2·69, p=2×10(-10)).

INTERPRETATION

Some genetic mechanisms that raise plasma HDL cholesterol do not seem to lower risk of myocardial infarction. These data challenge the concept that raising of plasma HDL cholesterol will uniformly translate into reductions in risk of myocardial infarction.

FUNDING

US National Institutes of Health, The Wellcome Trust, European Union, British Heart Foundation, and the German Federal Ministry of Education and Research.

P.R4810K, a polymorphism of RNF213, the susceptibility gene for moyamoya disease, is associated with blood pressure

BACKGROUND

Moyamoya disease-an idiopathic vascular disorder of intracranial arteries-is often accompanied by hypertension. RNF213 has been identified as a susceptibility gene for moyamoya disease. In the present study, the association of p.R4810K (G>A) with blood pressure (BP) was investigated in a Japanese population.

METHODOLOGY/PRINCIPAL FINDINGS

Three independent study populations, the Nyukawa (n = 984), Noshiro (n = 2,443) and Field (n = 881) studies, joined this study. BP, body weight and height were measured. Past and present symptoms and disease and medication histories were assessed by interview. Associations of p.R4810K (rs112735431, ss179362673) of RNF213 with BP were investigated. Two linkage disequilibrium blocks were constructed for moyamoya patients with p.R4810K (n = 140) and the general population (n = 384) using 39 single nucleotide polymorphisms (SNPs) spanning 390 kb around RNF213. A total of 60 carriers (3 for AA genotype and 57 for GA genotype) were found in these samples, and the minor allele frequencies were 1.4 % in the Nyukawa and Field studies and 0.2 % in the Noshiro study. Regression analyses adjusted for age, sex and body mass index based on an additive model demonstrated significant associations with systolic BP (mmHg/allele): β (standard error) was 8.2 (2.9) in the Nyukawa study (P = 4.7 × 10(-3)), 18.7 (5.4) in the Noshiro study (P = 4.6 × 10(-4)) and 8.9 (2.0) (P = 1.0 × 10(-5)) in the three populations. In contrast, diastolic BP showed significant associations only in the Noshiro study. Linkage disequilibrium blocks contained none of the BP-associated proxy SNPs reported by previous studies.

CONCLUSIONS/SIGNIFICANCE

Our study suggests that p.R4810K of RNF213 is associated strongly with systolic BP.

The metabochip, a custom genotyping array for genetic studies of metabolic, cardiovascular, and anthropometric traits

Genome-wide association studies have identified hundreds of loci for type 2 diabetes, coronary artery disease and myocardial infarction, as well as for related traits such as body mass index, glucose and insulin levels, lipid levels, and blood pressure. These studies also have pointed to thousands of loci with promising but not yet compelling association evidence. To establish association at additional loci and to characterize the genome-wide significant loci by fine-mapping, we designed the "Metabochip," a custom genotyping array that assays nearly 200,000 SNP markers. Here, we describe the Metabochip and its component SNP sets, evaluate its performance in capturing variation across the allele-frequency spectrum, describe solutions to methodological challenges commonly encountered in its analysis, and evaluate its performance as a platform for genotype imputation. The metabochip achieves dramatic cost efficiencies compared to designing single-trait follow-up reagents, and provides the opportunity to compare results across a range of related traits. The metabochip and similar custom genotyping arrays offer a powerful and cost-effective approach to follow-up large-scale genotyping and sequencing studies and advance our understanding of the genetic basis of complex human diseases and traits.

Hypothesis-based analysis of gene-gene interactions and risk of myocardial infarction

The genetic loci that have been found by genome-wide association studies to modulate risk of coronary heart disease explain only a fraction of its total variance, and gene-gene interactions have been proposed as a potential source of the remaining heritability. Given the potentially large testing burden, we sought to enrich our search space with real interactions by analyzing variants that may be more likely to interact on the basis of two distinct hypotheses: a biological hypothesis, under which MI risk is modulated by interactions between variants that are known to be relevant for its risk factors; and a statistical hypothesis, under which interacting variants individually show weak marginal association with MI. In a discovery sample of 2,967 cases of early-onset myocardial infarction (MI) and 3,075 controls from the MIGen study, we performed pair-wise SNP interaction testing using a logistic regression framework. Despite having reasonable power to detect interaction effects of plausible magnitudes, we observed no statistically significant evidence of interaction under these hypotheses, and no clear consistency between the top results in our discovery sample and those in a large validation sample of 1,766 cases of coronary heart disease and 2,938 controls from the Wellcome Trust Case-Control Consortium. Our results do not support the existence of strong interaction effects as a common risk factor for MI. Within the scope of the hypotheses we have explored, this study places a modest upper limit on the magnitude that epistatic risk effects are likely to have at the population level (odds ratio for MI risk 1.3-2.0, depending on allele frequency and interaction model).

Multiple genetic variants explain measurable variance in type 2 diabetes-related traits in Pakistanis

AIMS/HYPOTHESIS

Multiple genetic variants are associated with type 2 diabetes-related traits in Europeans, but their role in South Asian populations needs further study. We hypothesised that genetic variants associated with diabetes-related traits in Europeans would explain a similar proportion of phenotypic variance in a Pakistani population and could be used in Mendelian randomisation analyses.

METHODS

We used data from 2,131 individuals from the Control of Blood Pressure and Risk Attenuation Trial (COBRA) in Karachi, Pakistan. Individuals were aged 40 years or older.

RESULTS

Combining information from multiple genetic variants showed that fasting glucose, BMI, triacylglycerol, and systolic and diastolic blood pressure variants explained 2.9%, 0.7%, 5.5%, 1.2% and 1.8% of the variance in those traits respectively. Genetic risk scores of fasting glucose, triacylglycerol, BMI, systolic blood pressure and diastolic blood pressure variants were associated with these traits, with per allele SD effects of 0.057 (95% CI 0.041, 0.074), p=3.44 × 10(-12), 0.130 (95% CI 0.105, 0.155), p=2.9 × 10(-21), 0.04 (95% CI 0.014, 0.072), p=0.004, 0.031 (95% CI 0.016, 0.047), p=7.9 × 10(-5), 0.028 (95% CI 0.015, 0.042), p = 5.5 × 10(-5), respectively. These effects are consistent with those observed in Europeans, except that the effect of triacylglycerol variants in South Asians was slightly lower. Mendelian randomisation provided evidence that genetically influenced, raised triacylglycerol levels do not causally affect type 2 diabetes risk to the extent predicted from observational data (p=0.0003 for difference between observed and instrumental variables correlations).

CONCLUSIONS/INTERPRETATION

Genetic variants identified in Europeans are associated with type 2 diabetes-related traits in Pakistanis, with comparable effect sizes. Larger studies are needed to perform adequately powered Mendelian randomisation and help dissect the relationships between type 2 diabetes-related traits in diverse South Asian subgroups.

Gene expression profiles in white blood cells of volunteers exposed to a 50 Hz electromagnetic field

Consistent and independently replicated laboratory evidence to support a causative relationship between environmental exposure to extremely low-frequency electromagnetic fields (EMFs) at power line frequencies and the associated increase in risk of childhood leukemia has not been obtained. In particular, although gene expression responses have been reported in a wide variety of cells, none has emerged as robust, widely replicated effects. DNA microarrays facilitate comprehensive searches for changes in gene expression without a requirement to select candidate responsive genes. To determine if gene expression changes occur in white blood cells of volunteers exposed to an ELF-EMF, each of 17 pairs of male volunteers age 20-30 was subjected either to a 50 Hz EMF exposure of 62.0 ± 7.1 μT for 2 h or to a sham exposure (0.21 ± 0.05 μT) at the same time (11:00 a.m. to 13:00 p.m.). The alternative regime for each volunteer was repeated on the following day and the two-day sequence was repeated 6 days later, with the exception that a null exposure (0.085 ± 0.01 μT) replaced the sham exposure. Five blood samples (10 ml) were collected at 2 h intervals from 9:00 to 17:00 with five additional samples during the exposure and sham or null exposure periods on each study day. RNA samples were pooled for the same time on each study day for the group of 17 volunteers that were subjected to the ELF-EMF exposure/sham or null exposure sequence and were analyzed on Illumina microarrays. Time courses for 16 mammalian genes previously reported to be responsive to ELF-EMF exposure, including immediate early genes, stress response, cell proliferation and apoptotic genes were examined in detail. No genes or gene sets showed consistent response profiles to repeated ELF-EMF exposures. A stress response was detected as a transient increase in plasma cortisol at the onset of either exposure or sham exposure on the first study day. The cortisol response diminished progressively on subsequent exposures or sham exposures, and was attributable to mild stress associated with the experimental protocol.

Mapping genetic variants associated with beta-adrenergic responses in inbred mice

β-blockers and β-agonists are primarily used to treat cardiovascular diseases. Inter-individual variability in response to both drug classes is well recognized, yet the identity and relative contribution of the genetic players involved are poorly understood. This work is the first genome-wide association study (GWAS) addressing the values and susceptibility of cardiovascular-related traits to a selective β₁-blocker, Atenolol (ate), and a β-agonist, Isoproterenol (iso). The phenotypic dataset consisted of 27 highly heritable traits, each measured across 22 inbred mouse strains and four pharmacological conditions. The genotypic panel comprised 79922 informative SNPs of the mouse HapMap resource. Associations were mapped by Efficient Mixed Model Association (EMMA), a method that corrects for the population structure and genetic relatedness of the various strains. A total of 205 separate genome-wide scans were analyzed. The most significant hits include three candidate loci related to cardiac and body weight, three loci for electrocardiographic (ECG) values, two loci for the susceptibility of atrial weight index to iso, four loci for the susceptibility of systolic blood pressure (SBP) to perturbations of the β-adrenergic system, and one locus for the responsiveness of QTc (p<10⁻⁸). An additional 60 loci were suggestive for one or the other of the 27 traits, while 46 others were suggestive for one or the other drug effects (p<10⁻⁶). Most hits tagged unexpected regions, yet at least two loci for the susceptibility of SBP to β-adrenergic drugs pointed at members of the hypothalamic-pituitary-thyroid axis. Loci for cardiac-related traits were preferentially enriched in genes expressed in the heart, while 23% of the testable loci were replicated with datasets of the Mouse Phenome Database (MPD). Altogether these data and validation tests indicate that the mapped loci are relevant to the traits and responses studied.

Dahl (S x R) congenic strain analysis confirms and defines a chromosome 5 female-specific blood pressure quantitative trait locus to <7 Mbp

The detection of multiple sex-specific blood pressure (BP) quantitative trait loci (QTLs) in independent total genome analyses of F2 (Dahl S x R)-intercross male and female rat cohorts confirms clinical observations of sex-specific disease cause and response to treatment among hypertensive patients, and mandate the identification of sex-specific hypertension genes/mechanisms. We developed and studied two congenic strains, S.R5A and S.R5B introgressing Dahl R-chromosome 5 segments into Dahl S chromosome 5 region spanning putative BP-f1 and BP-f2 QTLs. Radiotelemetric non-stressed 24-hour BP analysis at four weeks post-high salt diet (8% NaCl) challenge, identified only S.R5B congenic rats with lower SBP (−26.5 mmHg, P = 0.002), DBP (−23.7 mmHg, P = 0.004) and MAP (−25.1 mmHg, P = 0.002) compared with Dahl S female controls at four months of age confirming BP-f1 but not BP-f2 QTL on rat chromosome 5. The S.R5B congenic segment did not affect pulse pressure and relative heart weight indicating that the gene underlying BP-f1 does not influence arterial stiffness and cardiac hypertrophy. The results of our congenic analysis narrowed BP-f1 to chromosome 5 coordinates 134.9–141.5 Mbp setting up the basis for further fine mapping of BP-f1 and eventual identification of the specific gene variant accounting for BP-f1 effect on blood pressure.

Childhood Physical, Environmental, and Genetic Predictors of Adult Hypertension

Background—

Hypertension is a major modifiable cardiovascular risk factor. The present longitudinal study aimed to examine the best combination of childhood physical and environmental factors to predict adult hypertension and furthermore whether newly identified genetic variants for blood pressure increase the prediction of adult hypertension.

Methods and Results—

The study cohort included 2625 individuals from the Cardiovascular Risk in Young Finns Study who were followed up for 21 to 27 years since baseline (1980; age, 3–18 years). In addition to dietary factors and biomarkers related to blood pressure, we examined whether a genetic risk score based on 29 newly identified single-nucleotide polymorphisms enhances the prediction of adult hypertension. Hypertension in adulthood was defined as systolic blood pressure ≥130 mm Hg and/or diastolic blood pressure ≥85 mm Hg or medication for the condition. Independent childhood risk factors for adult hypertension included the individual's own blood pressure ( P <0.0001), parental hypertension ( P <0.0001), childhood overweight/obesity ( P =0.005), low parental occupational status ( P =0.003), and high genetic risk score ( P <0.0001). Risk assessment based on childhood overweight/obesity status, parental hypertension, and parental occupational status was superior in predicting hypertension compared with the approach using only data on childhood blood pressure levels (C statistics, 0.718 versus 0.733; P =0.0007). Inclusion of both parental hypertension history and data on novel genetic variants for hypertension further improved the C statistics (0.742; P =0.015).

Conclusions—

Prediction of adult hypertension was enhanced by taking into account known physical and environmental childhood risk factors, family history of hypertension, and novel genetic variants. A multifactorial approach may be useful in identifying children at high risk for adult hypertension.

Functional epistatic interaction between rs6046G>A in F7 and rs5355C>T in SELE modifies systolic blood pressure levels

Background

Although numerous genetic studies have been performed, only 0.9% of blood pressure phenotypic variance has been elucidated. This phenomenon could be partially due to epistatic interactions. Our aim was to identify epistatic interaction(s) associated with blood pressure levels in a pre-planned two-phase approach.

Methods and Results

In a discovery cohort composed of 3,600 French individuals, we found rs6046A allele in F7 associated with decreased blood pressure levels (P≤3.7×10⁻³) and rs5355T allele in SELE associated with decreased diastolic blood pressure levels (P = 5×10⁻³). Both variants interacted in order to influence blood pressure levels (P≤0.048). This interaction was replicated with systolic blood pressure in 4,620 additional European individuals (P = 0.03). Similarly, in this replication cohort, rs6046A was associated with decreased blood pressure levels (P≤8.5×10⁻⁴). Furthermore, in peripheral blood mononuclear cells of a subsample of 90 supposed healthy individuals, we found rs6046A positively associated with NAMPT mRNA levels (P≤9.1×10⁻⁵), suggesting an eventual involvement of NAMPT expression in blood pressure regulation. Confirming this hypothesis, further transcriptomic analyses showed that increased NAMPT mRNA levels were positively correlated with ICAM1, SELL, FPR1, DEFA1-3, and LL-37 genes expression (P≤5×10⁻³). The last two mRNA levels were positively associated with systolic blood pressure levels (P≤0.01) and explained 4% of its phenotypic variation.

Conclusion

These findings reveal the importance of epistatic interactions in blood pressure genetics and give new insights for the role of inflammation in its complex regulation.

Hypertension: management perspectives

INTRODUCTION

The increasing worldwide prevalence of hypertension and the related increase in cost due to diagnosis, management and negative outcomes forces public health institutions and clinical researchers to find new strategies to improve blood pressure (BP) control. So what are the possible future perspectives for high BP management?

AREAS COVERED

Three main points are briefly discussed in this article: individualized therapy, the known genetic contribution to hypertension development and control, and the improvement of disease management, including perspectives on new antihypertensive drug development.

EXPERT OPINION

It is likely that the integration of the best available current knowledge with recent diagnostic and therapeutic achievements for the management of hypertension prevention and treatment will lead to the early detection of at-risk conditions, early diagnosis, and individualized and efficacious treatment. The most promising antihypertensive drugs currently in development are innovative renin-angiotensin-aldosterone system modulators. Further drugs have potentially interesting mechanisms of action, but renalase analogs are in the very early phases of development, and available endothelin antagonists have a poor safety profile.

Validated SNPs for eGFR and their associations with albuminuria

Albuminuria and reduced glomerular filtration rate are manifestations of chronic kidney disease (CKD) that predict end-stage renal disease, acute kidney injury, cardiovascular disease and death. We hypothesized that SNPs identified in association with the estimated glomerular filtration rate (eGFR) would also be associated with albuminuria. Within the CKDGen Consortium cohort (n= 31 580, European ancestry), we tested 16 eGFR-associated SNPs for association with the urinary albumin-to-creatinine ratio (UACR) and albuminuria [UACR >25 mg/g (women); 17 mg/g (men)]. In parallel, within the CARe Renal Consortium (n= 5569, African ancestry), we tested seven eGFR-associated SNPs for association with the UACR. We used a Bonferroni-corrected P-value of 0.003 (0.05/16) in CKDGen and 0.007 (0.05/7) in CARe. We also assessed whether the 16 eGFR SNPs were associated with the UACR in aggregate using a beta-weighted genotype score. In the CKDGen Consortium, the minor A allele of rs17319721 in the SHROOM3 gene, known to be associated with a lower eGFR, was associated with lower ln(UACR) levels (beta = -0.034, P-value = 0.0002). No additional eGFR-associated SNPs met the Bonferroni-corrected P-value threshold of 0.003 for either UACR or albuminuria. In the CARe Renal Consortium, there were no associations between SNPs and UACR with a P< 0.007. Although we found the genotype score to be associated with albuminuria (P= 0.0006), this result was driven almost entirely by the known SHROOM3 variant, rs17319721. Removal of rs17319721 resulted in a P-value 0.03, indicating a weak residual aggregate signal. No alleles, previously demonstrated to be associated with a lower eGFR, were associated with the UACR or albuminuria, suggesting that there may be distinct genetic components for these traits.

Meta-analysis identifies multiple loci associated with kidney function-related traits in east Asian populations

Chronic kidney disease (CKD), impairment of kidney function, is a serious public health problem, and the assessment of genetic factors influencing kidney function has substantial clinical relevance. Here, we report a meta-analysis of genome-wide association studies for kidney function-related traits, including 71,149 east Asian individuals from 18 studies in 11 population-, hospital- or family-based cohorts, conducted as part of the Asian Genetic Epidemiology Network (AGEN). Our meta-analysis identified 17 loci newly associated with kidney function-related traits, including the concentrations of blood urea nitrogen, uric acid and serum creatinine and estimated glomerular filtration rate based on serum creatinine levels (eGFRcrea) (P < 5.0 × 10(-8)). We further examined these loci with in silico replication in individuals of European ancestry from the KidneyGen, CKDGen and GUGC consortia, including a combined total of ∼110,347 individuals. We identify pleiotropic associations among these loci with kidney function-related traits and risk of CKD. These findings provide new insights into the genetics of kidney function.