The thiazide-sensitive Na(+)-Cl(-) cotransporter gene, C1784T, and adrenergic receptor-beta3 gene, T727C, may be gene polymorphisms susceptible to the antihypertensive effect of thiazide diuretics

Sensitive detection of single-nucleotide polymorphisms by conjugated polymers for personalized treatment of hypertension

Genetic variants among individuals have been associated with ineffective control of hypertension. Previous work has shown that hypertension has a polygenic nature, and interactions between these loci have been associated with variations in drug response. Rapid detection of multiple genetic loci with high sensitivity and specificity is needed for the effective implementation of personalized medicine for the treatment of hypertension. Here, we used a cationic conjugated polymer (CCP)-based multistep fluorescence resonance energy transfer (MS-FRET) technique to qualitatively analyze DNA genotypes associated with hypertension in the Chinese population. Assessment of 10 genetic loci using this technique successfully identified known hypertensive risk alleles in a retrospective study of whole-blood samples from 150 patients hospitalized with hypertension. We then applied our detection method in a prospective clinical trial of 100 patients with essential hypertension and found that personalized treatment of patients with hypertension based on results from the MS-FRET technique could effectively improve blood pressure control rate (94.0% versus 54.0%) and shorten the time duration to controlling blood pressure (4.06 ± 2.10 versus 5.82 ± 1.84 days) as compared with conventional treatment. These results suggest that CCP-based MS-FRET genetic variant detection may assist clinicians in rapid and accurate classification of risk in patients with hypertension and improve treatment outcomes.

SLC12A3 Variation and Renal Function in Chinese Patients With Hypertension

Objective

SLC12A3 (solute carrier family 12 member 3) gene variants are associated with diabetic nephropathy; however, their association with hypertensive nephropathy remains unknown. We aimed to investigate the association between SLC12A3 gene polymorphisms and renal function in patients with hypertension.

Methods

Participants from three non-diabetic hypertensive cohorts, including young-onset hypertension (cohort 1, n = 882), treatment-naïve hypertension (cohort 2, n = 90), and follow-up cohort (cohort 3, n = 166), underwent genotyping for single nucleotide polymorphisms in SLC12A3. Renal events were defined as a >25 and >50% decline in estimated glomerular filtration rate (eGFR).

Results

In cohort 1, SLC12A3 rs16963397 C/C or C/G (P = 0.005), rs13334864 C/C or C/T (P = 0.020), and rs7187932 A/A or A/G polymorphisms (P = 0.014) had higher eGFRs compared to their counterparts, with similar findings observed in cohort 2. In cohort 3, over a mean follow-up of 5.8 ± 1.7 years, participants with either SLC12A3 rs16963397 C/C or rs13334864 C/C polymorphisms had more >25 and >50% eGFR decline than their counterparts (log-rank test, P = 0.058 and P = 0.038, respectively). Cox regression analysis revealed that SLC12A3 rs16963397 C/C and rs13334864 C/C polymorphisms were significantly associated with an increased risk of >25% [hazard ratio (HR), 3.294; 95% confidence interval (CI), 1.158–9.368; P = 0.025] and >50% decline in eGFR (HR, 18.630; 95% CI, 1.529–227.005, P = 0.022) than their counterparts.

Conclusion

SLC12A3 polymorphisms are associated with renal function in Chinese patients with hypertension.

Activation of the Thiazide-Sensitive Sodium-Chloride Cotransporter by Beta3-Adrenoreceptor in the Distal Convoluted Tubule

We previously showed that the beta-3 adrenergic receptor (BAR3) is expressed in most segments of the nephron where its agonism promotes a potent antidiuretic effect. We localized BAR3 in distal convoluted tubule (DCT) cells expressing the thiazide-sensitive sodium-chloride cotransporter (NCC). Aim of this study is to investigate the possible functional role of BAR3 on NCC modulation in DCT cells. Here, we found that, in mice, the knockout of BAR3 was paralleled by a significant attenuation of NCC phosphorylation, paralleled by reduced expression and activation of STE-20/SPS1-related proline-alanine-rich kinase (SPAK) and WNKs the main kinases involved in NCC activation. Conversely, in BAR1/2 knockout mice, we found reduced NCC abundance with no changes in the phosphorylation state of NCC. Moreover, selective BAR3 agonism promotes both SPAK and NCC activation in wild-type mouse kidney slices. In conclusion, our findings suggest a novel role for BAR3 in the regulation of NCC in DCT.

Review and Analysis of Two Gitelman Syndrome Pedigrees Complicated with Proteinuria or Hashimoto's Thyroiditis Caused by Compound Heterozygous SLC12A3 Mutations

Gitelman syndrome (GS) is an autosomal recessive inherited salt-losing renal tubular disease, which is caused by a pathogenic mutation of SLC12A3 encoding thiazide-sensitive Na-Cl cotransporter, which leads to disturbance of sodium and chlorine reabsorption in renal distal convoluted tubules, resulting in phenotypes such as hypovolemia, renin angiotensin aldosterone system (RAAS) activation, hypokalemia, and metabolic alkalosis. In this study, two GS families with proteinuria or Hashimoto's thyroiditis were analyzed for genetic-phenotypic association. Sanger sequencing revealed that two probands carried SLC12A3 compound heterozygous mutations, and proband A carried two pathogenic mutations: missense mutation Arg83Gln, splicing mutation, or frameshift mutation NC_000016.10:g.56872655_56872667 (gcggacatttttg>accgaaaatttt) in exon 8. Proband B carries two missense mutations: novel Asp839Val and Arg904Gln. Both probands manifested hypokalemia, hypomagnesemia, hypocalcinuria, metabolic alkalosis, and RAAS activation; in addition, the proband A exhibited decreased urinary chloride, phosphorus, and increased magnesium ions excretion, complicated with Hashimoto's Thyroiditis, while the proband B exhibited enhanced urine sodium excretion and proteinuria. The older sister of proband B with GS also had Hashimoto's thyroiditis. Electron microscopy revealed swelling and vacuolar degeneration of glomerular epithelial cells, diffuse proliferation of mesangial cells and matrix, accompanied by a small amount of low-density electron-dense deposition, and segmental fusion of epithelial cell foot processes in proband B. Light microscopy showed mild mesangial hyperplasia in the focal segment of the glomerulus, hyperplasia, and hypertrophy of juxtaglomerular apparatus cells, mild renal tubulointerstitial lesions, and one glomerular sclerosis. So, long-term hypokalemia of GS can cause kidney damage and may also be susceptible to thyroid disease.

Genetics of Human Primary Hypertension: Focus on Hormonal Mechanisms

Increasingly, primary hypertension is being considered a syndrome and not a disease, with the individual causes (diseases) having a common sign-an elevated blood pressure. To determine these causes, genetic tools are increasingly employed. This review identified 62 proposed genes. However, only 21 of them met our inclusion criteria: (i) primary hypertension, (ii) two or more supporting cohorts from different publications or within a single publication or one supporting cohort with a confirmatory genetically modified animal study, and (iii) 600 or more subjects in the primary cohort; when including our exclusion criteria: (i) meta-analyses or reviews, (ii) secondary and monogenic hypertension, (iii) only hypertensive complications, (iv) genes related to blood pressure but not hypertension per se, (v) nonsupporting studies more common than supporting ones, and (vi) studies that did not perform a Bonferroni or similar multiassessment correction. These 21 genes were organized in a four-tiered structure: distant phenotype (hypertension); intermediate phenotype [salt-sensitive (18) or salt-resistant (0)]; subintermediate phenotypes under salt-sensitive hypertension [normal renin (4), low renin (8), and unclassified renin (6)]; and proximate phenotypes (specific genetically driven hypertensive subgroup). Many proximate hypertensive phenotypes had a substantial endocrine component. In conclusion, primary hypertension is a syndrome; many proposed genes are likely to be false positives; and deep phenotyping will be required to determine the utility of genetics in the treatment of hypertension. However, to date, the positive genes are associated with nearly 50% of primary hypertensives, suggesting that in the near term precise, mechanistically driven treatment and prevention strategies for the specific primary hypertension subgroups are feasible.

Arg913Gln of SLC12A3 gene promotes development and progression of end-stage renal disease in Chinese type 2 diabetes mellitus

Whether the Arg913Gln variation (rs11643718, G/A) of SLC12A3 contributes to diabetic nephropathy (DN) remains controversial. We undertook a case-control study to evaluate the association of the SLC12A3-Arg913Gln variation with the risk of end-stage renal disease (ESRD) in Chinese type 2 diabetes mellitus (T2DM) patients undergoing hemodialysis, and analyzed the genotype-phenotype interaction. Unrelated Chinese T2DM patients (n = 372) with diabetic retinopathy were classified into the non-DN (control) group (n = 151; duration of T2DM >15 years, no signs of renal involvement) and the DN-ESRD group (n = 221; ESRD due to T2DM, receiving hemodialysis). Polymerase chain reaction-direct sequencing was used to genotype the SLC12A3-Arg913Gln variation for all participants. The frequency of the GA+AA genotype in the DN-ESRD group was significantly higher than that of the non-DN group (23.1 vs. 9.9%; adjusted OR 2.2 (95% CI 1.3-4.5), P = 0.019). In the non-DN group, GA+AA carriers had a significantly higher urinary albumin excretion rate (UAER) and diastolic blood pressure compared with GG carriers (both P < 0.05). The SLC12A3-Arg913Gln variation may be associated with increased blood pressure and UAER and, therefore, could be used to predict the development and progression of DN-ESRD in Chinese T2DM patients undergoing hemodialysis.

β3 adrenergic receptor in the kidney may be a new player in sympathetic regulation of renal function

To date, the study of the sympathetic regulation of renal function has been restricted to the important contribution of β1- and β2-adrenergic receptors (ARs). Here we investigate the expression and the possible physiologic role of β3-adrenergic receptor (β3-AR) in mouse kidney. The β3-AR is expressed in most of the nephron segments that also express the type 2 vasopressin receptor (AVPR2), including the thick ascending limb and the cortical and outer medullary collecting duct. Ex vivo experiments in mouse kidney tubules showed that β3-AR stimulation with the selective agonist BRL37344 increased intracellular cAMP levels and promoted 2 key processes in the urine concentrating mechanism. These are accumulation of the water channel aquaporin 2 at the apical plasma membrane in the collecting duct and activation of the Na-K-2Cl symporter in the thick ascending limb. Both effects were prevented by the β3-AR antagonist L748,337 or by the protein kinase A inhibitor H89. Interestingly, genetic inactivation of β3-AR in mice was associated with significantly increased urine excretion of water, sodium, potassium, and chloride. Stimulation of β3-AR significantly reduced urine excretion of water and the same electrolytes. Moreover, BRL37344 promoted a potent antidiuretic effect in AVPR2-null mice. Thus, our findings are of potential physiologic importance as they uncover the antidiuretic effect of β3-AR stimulation in the kidney. Hence, β3-AR agonism might be useful to bypass AVPR2-inactivating mutations.

A Physiologic Approach to the Pharmacogenomics of Hypertension

Hypertension is a multifactorial condition with diverse physiological systems contributing to its pathogenesis. Individuals exhibit significant variation in their response to antihypertensive agents. Traditional markers, such as age, gender, diet, plasma renin level, and ethnicity, aid in drug selection. However, this review explores the contribution of genetics to facilitate antihypertensive agent selection and predict treatment efficacy. The findings, reproducibility, and limitations of published studies are examined, with emphasis placed on candidate genetic variants affecting drug metabolism, the renin-angiotensin system, adrenergic signalling, and renal sodium reabsorption. Single-nucleotide polymorphisms identified and replicated in unbiased genome-wide association studies of hypertension treatment are reviewed to illustrate the evolving understanding of the disease's complex and polygenic pathophysiology. Implementation efforts at academic centers seek to overcome barriers to the broad adoption of pharmacogenomics in the treatment of hypertension. The level of evidence required to support the implementation of pharmacogenomics in clinical practice is considered.

Hypertension pharmacogenomics: in search of personalized treatment approaches

Cardiovascular and renal diseases are associated with many risk factors, of which hypertension is one of the most prevalent. Worldwide, blood pressure control is only achieved in ∼50% of those treated for hypertension, despite the availability of a considerable number of antihypertensive drugs from different pharmacological classes. Although many reasons exist for poor blood pressure control, a likely contributor is the inability to predict to which antihypertensive drug an individual is most likely to respond. Hypertension pharmacogenomics and other 'omics' technologies have the potential to identify genetic signals that are predictive of response or adverse outcome to particular drugs, and guide selection of hypertension treatment for a given individual. Continued research in this field will enhance our understanding of how to maximally deploy the various antihypertensive drug classes to optimize blood pressure response at the individual level. This Review summarizes the available literature on the most convincing genetic signals associated with antihypertensive drug responses and adverse cardiovascular outcomes. Future research in this area will be facilitated by enhancing collaboration between research groups through consortia such as the International Consortium for Antihypertensives Pharmacogenomics Studies, with the goal of translating replicated findings into clinical implementation.

Risk given by AGT polymorphisms in inducing susceptibility to essential hypertension among isolated populations from a remote region of China: A case-control study among the isolated populations

INTRODUCTION

Hypertension is a serious risk factor affecting up to 30% of the world's population with a heritability of more than 30-50%. The aim of this study was to investigate the contribution of the polymorphisms localized in the angiotensinogen (AGT) gene, a main component of the renin-angiotensin-aldosterone system, in inducing the susceptibility to essential hypertension (EH) among isolated populations (Yi and Hani minorities) with low prevalence rate from the remote region of Yunnan in China.

METHODS

A case-control association study was performed, and all subjects were genotyped for the seven single nucleotide polymorphisms localized in the AGT region by polymerase chain reaction-restriction fragment length polymorphism analysis.

RESULTS

Three polymorphisms, i.e. rs5046, rs5049, and rs2478544, were significantly associated with EH among the Hani minority. The associations, found in the Yi minority, did not reach a conclusive level of statistical significance. The polymorphisms of rs2478544 and rs5046 caused the transformations of exonic splicing enhancer sites and transcription factor binding sites, respectively, in the bioinformatic analyses. The haplotype-rs5046T, rs5049A, rs11568020G, rs3789679C, rs2478544C was susceptible for EH among the Hani minority.

CONCLUSION

Our findings suggested that the AGT polymorphisms have played a vital role in determining an individual's susceptibility to EH among the isolated population, which would be helpful for EH management in the remote mountainous region of Yunnan in China.

Thiazide-sensitive Na+-Cl- cotransporter: genetic polymorphisms and human diseases

The thiazide-sensitive Na(+)-Cl(-) cotransporter (TSC) is responsible for the major sodium chloride reabsorption pathway, which is located in the apical membrane of the epithelial cells of the distal convoluted tubule. TSC is involved in several physiological activities including transepithelial ion absorption and secretion, cell volume regulation, and setting intracellular Cl(-) concentration below or above its electrochemical potential equilibrium. In addition, TSC serves as the target of thiazide-type diuretics that are the first line of therapy for the treatment of hypertension in the clinic, and its mutants are also reported to be associated with the hereditary disease, Gitelman's syndrome. This review aims to summarize the publications with regard to the TSC by focusing on the association between TSC mutants and human hypertension as well as Gitelman's syndrome.

Extracellular water and blood pressure in adults with growth hormone (GH) deficiency: a genotype-phenotype association study

Objectives

Growth hormone deficiency (GHD) in adults is associated with decreased extracellular water volume (ECW). In response to GH replacement therapy (GHRT), ECW increases and blood pressure (BP) reduces or remains unchanged. Our primary aim was to study the association between polymorphisms in genes related to renal tubular function with ECW and BP before and 1 year after GHRT. The ECW measures using bioimpedance analysis (BIA) and bioimpedance spectroscopy (BIS) were validated against a reference method, the sodium bromide dilution method (Br⁻).

Design and Methods

Using a candidate gene approach, fifteen single-nucleotide polymorphisms (SNPs) in nine genes with known impact on renal tubular function (AGT, SCNN1A, SCNN1G, SLC12A1, SLC12A3, KCNJ1, STK39, WNK1 and CASR) were genotyped and analyzed for associations with ECW and BP at baseline and with their changes after 1 year of GHRT in 311 adult GHD patients. ECW was measured with the Br⁻, BIA, and BIS.

Results

Both BIA and BIS measurements demonstrated similar ECW results as the reference method. At baseline, after adjustment for sex and BMI, SNP rs2291340 in the SLC12A1 gene was associated with ECW volume in GHD patients (p = 0.039). None of the SNPs influenced the ECW response to GHRT. One SNP in the SLC12A3 gene (rs11643718; p = 0.024) and three SNPs in the SCNN1G gene [rs5723 (p = 0.02), rs5729 (p = 0.016) and rs13331086 (p = 0.035)] were associated with the inter-individual differences in BP levels at baseline. A polymorphism in the calcium-sensing receptor (CASR) gene (rs1965357) was associated with changes in systolic BP after GHRT (p = 0.036). None of these associations remained statistically significant when corrected for multiple testing.

Conclusion

The BIA and BIS are as accurate as Br⁻ to measure ECW in GHD adults before and during GHRT. Our study provides the first evidence that individual polymorphisms may have clinically relevant effects on ECW and BP in GHD adults.

Genetic predictors of thiazide-induced serum potassium changes in nondiabetic hypertensive patients

Thiazide diuretics are associated with an increased risk of hypokalemia. However, pharmacogenetic markers of thiazide-induced changes in serum potassium are not well studied. The aim of this study was to investigate possible predictors of serum potassium changes after thiazide treatment. Nondiabetic hypertensive patients with a systolic blood pressure of ⩾140 or a diastolic blood pressure of ⩾90 mm Hg were enrolled in our study. After 2 weeks of lifestyle modification and diet instruction, patients with persistently elevated blood pressure were given 50 mg of hydrochlorothiazide every morning for 2 weeks. Twenty single-nucleotide polymorphism (SNP) markers were selected from two candidate genes, SLC12A3 and WNK1. Serum potassium levels were checked before and after hydrochlorothiazide treatment. A total of 75 patients eventually qualified for enrollment in our study. They received 50 mg of hydrochlorothiazide every morning for 2 weeks. Six SNPs in WNK1 (rs11064524, rs4980973, rs12581940, rs880054, rs953361, and rs10849582) were correlated with decreases in serum potassium. None of the SLC12A3 polymorphisms were correlated with decreases in serum potassium. After Bonferroni's correction, only rs4980973 was correlated with decreases in serum potassium (corrected P=0.014). Multivariate stepwise linear regression analysis revealed that the changes in serum potassium levels were independently associated with the baseline potassium level (β=-0.587, 95% confidence interval=-0.875--0.299, P=0.0001) and WNK1 rs4980973 (A/A and A/G vs. G/G, β=-0.418, 95% confidence interval=-0.598--0.237, P=0.00002). In conclusion, the baseline potassium level and the WNK1 rs4980973 polymorphism were independent predictors of decreases in serum potassium after short-term hydrochlorothiazide treatment in nondiabetic hypertensive patients.

Effect of NR3C2 genetic polymorphisms on the blood pressure response to enalapril treatment

AIM

The mineralocorticoid receptor (MR; also known as NR3C2) plays important roles in the modulation of blood pressure. The effect of NR3C2 polymorphisms on antihypertensive response to enalapril was investigated.

PATIENTS & METHODS

Two hundred and seventy nine essential hypertension patients treated with enalapril were genotyped for two NR3C2 tagSNPs, rs5522 and rs2070950, by Sequenom MassArray™ technology.

RESULTS

The reductions in diastolic blood pressure (DBP) were significantly greater in AA homozygotes compared with AG+GG genotype carriers for the rs5522 polymorphism (p = 0.009), and the reductions in DBP were greater in GG homozygotes compared with GC+CC genotype carriers for the rs2070950 polymorphism, with marginal significance (p = 0.065). Stepwise multiple regression analysis indicated that significant predictors of DBP reduction were baseline DBP (p < 0.001), waist:hip ratio (p = 0.001) and rs5522 genotype (p = 0.003).

CONCLUSION

NR3C2 rs5522 affects blood pressure response to enalapril treatment and may serve as a useful pharmacogenomic marker of antihypertensive response to enalapril in essential hypertension patients.

Polymorphisms, hypertension and thiazide diuretics

It is 10 years since the discovery of the human genome; however, the study of the influence of genetic variants on drug effect - pharmacogenomics - has so far failed to create a major impact on day-to-day prescription practices. In the present article we analyze the main findings in candidate gene variants, gene combinations and whole-genome scans in relation to diuretic treatment. A critical analysis of the main reasons for some contrasting results will be discussed. The hypertension phases, in clinical trials dealing with genes and related pathophysiological mechanisms, may account for these inconsistent findings. The use of previously untreated versus treated patients is addressed. Finally, a positive study with a new genetic molecular strategy is described.

Genetic variation in renin predicts the effects of thiazide diuretics

BACKGROUND

While genetic variants of renin-angiotensin-aldosterone system (RAAS) may modify the blood pressure (BP) response to thiazide diuretics, there was no evidence of genetic variations in renin (REN) playing a role. This study aimed to address the potential effects of genetic variations of RAAS on the response to initial treatment of hydrochlorothiazide (HCTZ).

MATERIALS AND METHODS

We enrolled nondiabetic hypertensive patients with a systolic blood pressure (SBP) ≥140 or a diastolic blood pressure (DBP) ≥90mmHg, who were either previously untreated or unsatisfactorily treated. After lifestyle modification and diet instruction for 2weeks, 90 patients with persistently elevated BP were given HCTZ 50 mg every morning for 2 weeks. Single nucleotide polymorphism markers were selected from genes involving in RAAS, including rs7079 and rs699 of angiotensinogen, rs4293 and rs4353 of angiotensin-converting enzyme and rs1464816 and rs11240688 of REN.

RESULTS

The patients were divided into three groups according to the SBP response after HCTZ. The upper 1/3 responders had older age (P=0·035), higher SBP (P=0·039), higher pulse pressure (P=0·006) and lower plasma REN activity (PRA) (P=0·020) when compared with the lower 1/3 responders. Renin rs11240688 CC polymorphism (β=9·931, corrected P=0·012), Log PRA (β=7·451, P=0·004) and baseline SBP (β=0·299, P=0·006) were the independent predictors for the BP lowering response.

CONCLUSIONS

In addition to PRA, renin rs11240688 CC polymorphism may also independently predict the effect of HCTZ.

Novel genetic variants in the alpha-adducin and guanine nucleotide binding protein beta-polypeptide 3 genes and salt sensitivity of blood pressure

BACKGROUND

We examined the association between 12 single-nucleotide polymorphisms (SNPs) in the alpha-adducin (ADD1) and guanine nucleotide binding protein (G protein) beta-polypeptide 3 (GNB3) genes and systolic (SBP), diastolic (DBP), and mean arterial (MAP) pressure responses to salt intake.

METHODS

A 7-day low-sodium (51.3 mmol sodium/day) followed by a 7-day high-sodium intervention (307.8 mmol sodium/day) was conducted among 1,906 Han participants from rural North China. Blood pressure (BP) measurements were obtained at baseline and at the end of each intervention period using a random-zero sphygmomanometer.

RESULTS

We identified a significant association between a rare ADD1 variant rs17833172 and SBP, DBP, and MAP responses to high sodium (P values <0.0001) and DBP response to low sodium (P value = 0.002). Participants homozygous for the variant A allele of this marker had SBP, DBP, and MAP responses (95% confidence interval) to high salt of 1.6 (-1.8, 4.9), -0.8 (-5.6, 4.0), and -0.1 (-4.0, 3.9) mm Hg, respectively, vs. corresponding responses of 4.6 (2.5, 6.6), 1.7 (-0.2, 3.6), and 2.7 (0.9, 4.4) mm Hg, respectively, for those who were heterozygous or homozygous for the G allele. In addition, participants with at least one copy of the A allele of SNP rs1129649 of the GNB3 gene had significantly decreased MAP response to low salt compared to homozygotes for the C allele (P value = 0.004) with responses of -3.4 (-3.8, -3.0) vs. -4.2 (-4.6, -3.8) mm Hg, respectively.

CONCLUSIONS

These data support a role for the ADD1 and GNB3 genes in BP salt sensitivity. Future studies aimed at replicating these novel findings are warranted.

Association of a mineralocorticoid receptor gene polymorphism with hypertension in a Spanish population

BACKGROUND

To assess the association of polymorphisms and haplotypes of the mineralocorticoid receptor (MR) (NR3C2) gene to the risk of essential hypertension (HTN) in a Spanish population.

METHODS

This is a population-based study which included 1,502 subjects (748 women) >18 years old. Twenty-four polymorphisms of NR3C2 gene were analyzed by using SNPlex (Genotyping System based on OLA/PCR technology).

RESULTS

Alleles of the single-nucleotide polymorphism (SNP) rs5522 were significantly associated with the risk of HTN, both in the recessive and codominant models adjusted by age, gender, and body mass index (BMI). Genotype GG of the rs5522 showed to be protective against HTN odds ratio (OR) 0.10 (0.02-0.56), P < 0.01. One haplotype, which included the G allele of the rs5522, was also associated with reduced risk of HTN and four haplotypes which included the A allele were associated with increased risk of HTN. When the 24-h urinary sodium excretion and the estimated glomerular filtration rate (eGFR) were added, they did not reduce the significance level. Interaction between genotypes of the rs5522 and quartiles of 24-h sodium excretion has been observed. In subjects with the AA genotype, those with higher urinary sodium excretion had the lowest risk to be hypertensive.

CONCLUSION

A functional polymorphism of the NR3C2 gene was associated with risk of HTN. The data provided in this study seems to give credit to the hypothesis of the participation of MR gene in the development of HTN, although further studies are necessary to better assess its real impact.

Protein tyrosine kinase 2beta as a candidate gene for hypertension

Protein tyrosine kinase 2beta (PTK2B) is a member of the focal adhesion kinase family and is activated by angiotensin II through Ca2+-dependent pathways. An evidence exists that PTK2B is involved in cell growth, vascular contraction, inflammatory responses, and salt and water retention through activation of the angiotensin II type 1 receptor. To examine the contribution of PTK2B, we sequenced the PTK2B gene using 48 patients with hypertension, identified 62 genetic polymorphisms, and genotyped six representative single nucleotide polymorphisms in population-based case-control samples from 3655 Japanese individuals (1520 patients with hypertension and 2135 controls). Multivariate logistic regression analysis after adjustments for age, body mass index, present illness (hyperlipidemia and diabetes mellitus), and lifestyle (smoking and drinking) showed -22A>G to have an association with hypertension in men (AA vs. AG+GG: odds ratio=1.27; 95% confidence interval: 1.02-1.57; P=0.030). Another polymorphism, 53484A>C (K838T), in linkage disequilibrium with -22A>G showed a marginal association with hypertension in men (AA vs. AC+CC: odds ratio=1.25; 95% confidence interval: 0.99-1.57; P=0.059). Diastolic blood pressure was 1.6 mmHg higher in men with the AC+CC genotype of 53484A>C than those with the AA genotype (P=0.003), after adjustments for the same factors. These polymorphisms are in linkage disequilibrium with others in a range of 113 kb in PTK2B. The intracellular distribution of the recombinant PTK2B protein and that of the mutant protein with T838 were indistinguishable even after angiotensin II stimulation, both proteins localizing at a focal point in the peripheral area in the cells. Thus, a haplotype in PTK2B may play a role in essential hypertension in Japanese.

Molecular variants of the thiazide-sensitive Na+-Cl- cotransporter in hypertensive families

BACKGROUND

The thiazide-sensitive Na-Cl cotransporter (TSC) is involved in the fine regulation of sodium excretion by the kidney, and an increase in its activity causes salt-sensitive hypertension and hypercalciuria.

METHODS

To explore the possibility that activating mutations in the TSC gene may be involved in the pathogenesis of primary hypertension, we screened genomic DNA of 68 individuals from hypertensive families of patients with hypercalciuria for variations using single-strand conformation polymorphism and investigated the functional properties using the Xenopus laevis oocyte expression system.

RESULTS

We identified 18 variants in the TSC and, of those, four were nonsynonymous. The A728T, R904Q and R919C variants were introduced into the human TSC cDNA and expressed in Xenopus oocytes to study their effect on Na transport. Although T728 and Q904 did not show any difference in Na uptake, the R919C mutant showed a 60% increase compared to wild-type human TSC and an exaggerated inhibitory action of hydrochlorothiazide. Immunocytochemical analysis revealed no difference in cell surface expression of R919C mutants compared to wild-type hTSC. There was no significant difference in the inhibitory effect of the carboxyl terminus of the serine-threonine kinase WNK4 on the R919C mutant and wild-type hTSC.

CONCLUSIONS

Our results show that the substitution of arginine for cysteine at position 919 of TSC increases Na transport function, and provide support for the hypothesis that mutations in renal tubular sodium transporters may contribute to the development of primary hypertension, a polygenic disorder, by increasing renal sodium reabsorption.

Definition of phenotype

Definition of the phenotype is crucial in designing any genetic study, especially an association study, intended to detect the disease predisposing genes. In this chapter, we review the different types of phenotypes such as discrete or continuous and discuss the issues impacting on the phenotype definition related to study design, specifically, the impact of diagnostic error (misclassification) in case-control studies and measurement error in continuous traits. We show that the power of a study depends heavily on the phenotype measured and that misclassification or measurement error can dramatically reduce the power. We also suggest some possible responses to these challenges.

Pharmacogenomics and antihypertensive drugs: a path toward personalized medicine

Pharmacogenomics focuses on genes and the transcriptome and proteome. It has the potential to enhance healthcare management by improving disease diagnosis and implementing treatments adapted to each patient. Previously, pharmacogenetics of candidate genes focused on clinical research. It is now extended by using genome-wide approaches to elucidate the inherited basis of differences between individuals in their response to drugs. We summarize relevant polymorphisms of genes involved in the pharmacokinetics and pharmacodynamics of antihypertensive drugs and we give an overview of the state of pharmacogenomic research in hypertension medicine. Even if things are getting better, current pharmacogenetic studies still lack power, adequate selection of candidate genes and knowledge of their functions at the physiological level. Finally, some specific end point phenotypes (i.e., peptides or proteins related to the metabolic cycle targeted by the drug) should be integrated to propose data that are easily applicable to personalized medicine.

Genetic Variation in the Renal Sodium Transporters NKCC2, NCC, and ENaC in Relation to the Effects of Loop Diuretic Drugs

There is little data on genetic predictors of loop diuretic efficacy in humans. Therefore, we investigated the diuretic effects of single oral doses of bumetanide, frusemide, and torsemide in a crossover study in 97 healthy Caucasians in relation to genetic variation in the renal sodium transporters NKCC2 (coded by SLC12A1), NCC (SLC12A3), and ENaC (three subunits coded by SCNN1A, SCNN1B, and SCNN1G). The NCC alanine 264 allele (Gly264Ala) and the most frequent SCNN1B haplotype were associated with stronger diuresis, indicating lower reabsorbing function of these alleles. The variant alleles of the tightly coupled polymorphisms rs5723 (Leu649Leu) and rs5729 in SCNN1G were associated with weaker diuresis, indicating higher activity. Extended haplotype homozygosity implied evolutionary selection of the NCC alanine 264 allele. In conclusion, acute diuretic effects of loop diuretics were affected by genetic variation in sodium transporters that, in the nephron, are located distally from NKCC2.

Association of Genetic Polymorphisms of Endothelin-Converting Enzyme-1 Gene with Hypertension in a Japanese Population and Rare Missense Mutation in Preproendothelin-1 in Japanese Hypertensives

Endothelin-1 (EDN1), a 21-amino acid peptide, is a potent vasoconstrictor with various pharmacological responses. EDN1 is synthesized from a 212-amino acid precursor protein, preproEDN1, through multiple proteolytic steps. Endothelin-converting enzyme (ECE) cleaves a Trp73-Val74 peptide bond in big-EDN1 to give rise to mature EDN1. In this study, we examined the possible association of genetic variations in ECE1 with hypertension in a general Japanese population and searched for missense mutations in and around the EDN1 polypeptide. We genotyped 5 single nucleotide polymorphisms (SNPs) in the ECE1 gene in 1,873 individuals from a general Japanese population and identified one SNP associated with hypertension in women (rs212528: TT vs. TC+CC: odds ratio=1.40; 95% confidence intervals: 1.04-1.89; p=0.026), after adjusting for confounding factors. The systolic blood pressure in women with the CC genotype was 6.44 mmHg higher than that in those with the TT genotype (p=0.007), after adjusting for the same factors. Next, to identify the missense mutations that may influence the biological activity of EDN1, we sequenced the genomic region that encodes EDN1 in 942 Japanese hypertensive patients. We identified a novel missense mutation, G36R, in one hypertensive patient, but no mutations were observed in EDN1. A gene polymorphism in EDN1, Lys198Asn, has been reported to be associated with hypertension in obese subjects. Taken together, these findings reveal that the EDN-ECE pathway is an important system involved in essential hypertension in Japanese.

Genetic variations of HSD11B2 in hypertensive patients and in the general population, six rare missense/frameshift mutations

Mutations in the gene encoding 11beta-hydroxysteroid dehydrogenase type 2, HSD11B2, cause a rare monogenic juvenile hypertensive syndrome called apparent mineralocorticoid excess (AME). In AME, defective HSD11B2 enzyme activity results in overstimulation of the mineralocorticoid receptor (MR) by cortisol, causing sodium retention, hypokalemia, and salt-dependent hypertension. Here, we have studied whether genetic variations in HDS11B2 are implicated in essential hypertension in Japanese hypertensives and the general population. By sequencing the entire coding region and the promoter region of HDS11B2 in 953 Japanese hypertensives, we identified five missense mutations in 11 patients (L14F, n = 5; R74H, n = 1; R147H, n = 3; T156I, n = 1; R335H, n = 1) and one novel frameshift mutation (4884Gdel, n = 1) in a heterozygous state, in addition to 19 genetic variations. All genetic variations identified were rare, with minor allele frequencies less than 0.005. Four of 12 patients with the missense/frameshift mutations showed renal failure. Four missense mutations, L14F, R74H, R147H, and R335H, were successfully genotyped in the general population, with a sample size of 3,655 individuals (2,175 normotensives and 1,480 hypertensives). Mutations L14F, R74H, R147H, and R335H were identified in hypertensives (n = 6, 8, 3, and 0, respectively) and normotensives (n = 8, 12, 5, and 0, respectively) with a similar frequency, suggesting that these missense mutations may not strongly affect the etiology of essential hypertension. Since the allele frequency of all of the genetic variations identified in this study was rare, an association study was not conducted. Taken together, our results indicate that missense mutations in HSD11B2 do not substantially contribute to essential hypertension in Japanese.

The influence of the alpha-adducin G460W polymorphism and angiotensinogen M235T polymorphism on antihypertensive medication and blood pressure

Despite the availability of a variety of effective antihypertensive drugs, inadequate control of blood pressure is common in hypertensive patients. The aim of this study was investigate whether the alpha-adducin G460W polymorphism or angiotensinogen M235T polymorphism has an effect on the mean difference in blood pressure in subjects using antihypertensive drugs. Data from the Rotterdam Study, a population-based prospective cohort study in the Netherlands, was used. This study started in 1990 and included 7983 subjects of 55 years and older. Data from three examination rounds were used. Subjects were included when their blood pressure was elevated at 1 or more examinations and/or a diuretic, beta-blocker, calcium antagonist, or ACE inhibitor was used. A marginal generalized linear model was used to assess the drug-gene interaction. In total, 3025 hypertensives were included. No drug-gene interaction on blood pressure levels was found. The mean difference in systolic blood pressure (SBP) between subjects with the W-allele and GG genotype of the alpha-adducin gene was for diuretic users 1.25 mmHg (95% CI:-2.86 to 5.35), for beta-blockers 0.02 mmHg (95% CI:-3.39 to 3.42), for calcium antagonists -0.70 mmHg (95% CI:-5.61 to 4.21), and for ACE inhibitors -3.50 mmHg (95% CI:-9.02 to 2.02). The mean difference in SBP between subjects with the TT and MM genotype was for diuretic users -2.33 mmHg (95% CI:-8.32 to 3.66), for beta-blocker -0.06 mmHg (95% CI:-4.91 to 4.79), for calcium antagonist 0.59 mmHg (95% CI:-5.95 to 7.13), and for ACE inhibitor -2.33 mmHg (95% CI:-9.66 to 5.01). The G460W polymorphism and the M235T polymorphism did not modify the difference in blood pressure levels among subjects who used diuretics, beta-blockers, calcium antagonists, or ACE inhibitors.

SLC12A3 (solute carrier family 12 member [sodium/chloride] 3) polymorphisms are associated with end-stage renal disease in diabetic nephropathy

Diabetic nephropathy is the most common cause of end-stage renal disease (ESRD). Genetic susceptibility plays an important role in the development and progression of diabetic nephropathy. Previous studies have revealed that polymorphisms in the SLC12A3 (solute carrier family 12 member [sodium/chloride] 3) gene, which encodes solute carrier family 12 member 3, might contribute to genetic susceptibility to diabetic nephropathy and essential hypertension. In this study, we examined whether the SLC12A3 gene locus is associated with ESRD resulting from diabetic nephropathy. We genotyped 11 common single nucleotide polymorphisms (SNPs) in the SLC12A3 gene in 177 patients with ESRD due to type 2 diabetes and 184 patients with diabetic retinopathy but with no signs of renal involvement. Three SNPs (g.34372G>A [Arg913Gln], g.39143G>A, and g.41727C>T) were found to be associated with ESRD due to diabetic nephropathy. These three SNPs were in complete linkage disequilibrium. Haplotype 4 in block 2 (18806C, 21822C, 34372A, 39143A, 39240T, 39375C, and 41727T) showed a significant association with ESRD due to type 2 diabetes (P = 0.0028). These results suggest that the SLC12A3 gene locus is associated with ESRD due to diabetic nephropathy.

Update on G-protein polymorphisms in hypertension

The classic candidate gene approach continues to be the most prevalent tool in the search for the genetic basis of essential hypertension. With the list of candidate genes for this disorder steadily increasing, the pertussis toxin-sensitive inhibitory G protein (Gi) protein beta3 subunit (GNB3) gene has remained "sizzling," challenging the domination of the renin-angiotensin system. Is the genetic variability of GNB3 a causative factor underlying the pathogenesis of essential hypertension? Is the "functional" polymorphism, C825T, only "another" of the countless single nucleotide polymorphisms (SNP) for this disorder after all? As such, does its presence merely reinforce our confidence that essential hypertension is indeed polygenic? Should the C825T polymorphism be used in clinical practice and individualized antihypertensive treatment? Currently, there are still more questions than answers. In this review, in conjunction with our own research, we bring readers up to date on the latest developments of GNB3 polymorphisms in the field of hypertension.

Association of Sixty-One Non-Synonymous Polymorphisms in Forty-One Hypertension Candidate Genes with Blood Pressure Variation and Hypertension

We previously selected a group of hypertension candidate genes by a key word search using the OMIM database of NCBI and validated 525 coding single nucleotide polymorphisms (SNPs) in 179 hypertension candidate genes by DNA sequencing in a Japanese population. In the present study, we examined the association between 61 non-synonymous SNPs and blood pressure variations and hypertension. We used DNA samples taken from 1,880 subjects in the Suita study, a population-based study using randomly selected subjects. Analyses of covariance adjusting for age, body mass index, hyperlipidemia, diabetes, smoking, drinking, and antihypertensive medication revealed that 17 polymorphisms in 16 genes (APOB, CAST, CLCNKB, CTNS, GHR, GYS1, HF1, IKBKAP, KCNJ11, LIPC, LPL, P2RY2, PON2, SLC4A1, TRH, VWF) were significantly associated with blood pressure variations. Multivariate logistic regression analysis with adjustment for the same factors revealed that 11 polymorphisms in 11 genes (CAST, CTLA4, F5, GC, GHR, LIPC, PLA2G7, SLC4A1, SLCI8A1, TRH, VWF) showed significant associations with hypertension. Five polymorphisms in five genes, CAST(calpastatin), LIPC (hepatic lipase), SLC4A1 (band 3 anion transporter), TRH (thyrotropin-releasing hormone), and VWF (von Willebrand factor), were significantly associated with both blood pressure variation and hypertension. Thus, our study suggests that these five genes were susceptibility genes for essential hypertension in this Japanese population.