Genetics of renal mechanisms of primary hypertension: the role of adducin

A Review of the Epidemiological Evidence for Adducin Family Gene Polymorphisms and Hypertension

Hypertension is one of the most common cardiovascular diseases that seriously endangers human health and has become a significant public health problem worldwide. In the vast majority of patients, the cause of hypertension is unknown, called essential hypertension (EH), accounting for more than 95% of total hypertension. Epidemiological and genetic studies of humans and animals provide strong evidence of a causal relationship between high salt intake and hypertension. Adducin is one of the important candidate genes for essential hypertension. Adducin is a heterodimeric or heterotetrameric protein that consists of α, β, and γ subunits; the three subunits are encoded by genes (ADD1, ADD2, and ADD3) that map to three different chromosomes. Animal model experiments and clinical studies suggest that changes in single-nucleotide polymorphisms (SNPs) at part of the adducin family gene increase the Na⁺-K⁺-ATPase activity of the renal tubular basement membrane and increase the reabsorption of Na⁺ by renal tubular epithelial cells, which may cause hypertension. This review makes a summary on the structure, function, and mechanism of adducin and the role of adducin on the onset of EH, providing a basis for the early screening, prevention, and treatment of EH.

Clustering high-dimensional mixed data to uncover sub-phenotypes: joint analysis of phenotypic and genotypic data

The LIPGENE-SU.VI.MAX study, like many others, recorded high-dimensional continuous phenotypic data and categorical genotypic data. LIPGENE-SU.VI.MAX focuses on the need to account for both phenotypic and genetic factors when studying the metabolic syndrome (MetS), a complex disorder that can lead to higher risk of type 2 diabetes and cardiovascular disease. Interest lies in clustering the LIPGENE-SU.VI.MAX participants into homogeneous groups or sub-phenotypes, by jointly considering their phenotypic and genotypic data, and in determining which variables are discriminatory. A novel latent variable model that elegantly accommodates high dimensional, mixed data is developed to cluster LIPGENE-SU.VI.MAX participants using a Bayesian finite mixture model. A computationally efficient variable selection algorithm is incorporated, estimation is via a Gibbs sampling algorithm and an approximate BIC-MCMC criterion is developed to select the optimal model. Two clusters or sub-phenotypes ('healthy' and 'at risk') are uncovered. A small subset of variables is deemed discriminatory, which notably includes phenotypic and genotypic variables, highlighting the need to jointly consider both factors. Further, 7 years after the LIPGENE-SU.VI.MAX data were collected, participants underwent further analysis to diagnose presence or absence of the MetS. The two uncovered sub-phenotypes strongly correspond to the 7-year follow-up disease classification, highlighting the role of phenotypic and genotypic factors in the MetS and emphasising the potential utility of the clustering approach in early screening. Additionally, the ability of the proposed approach to define the uncertainty in sub-phenotype membership at the participant level is synonymous with the concepts of precision medicine and nutrition. Copyright © 2017 John Wiley & Sons, Ltd.

Genetic basis of the impaired renal myogenic response in FHH rats

This study examined the effect of substitution of a 2.4-megabase pair (Mbp) region of Brown Norway (BN) rat chromosome 1 (RNO1) between 258.8 and 261.2 Mbp onto the genetic background of fawn-hooded hypertensive (FHH) rats on autoregulation of renal blood flow (RBF), myogenic response of renal afferent arterioles (AF-art), K(+) channel activity in renal vascular smooth muscle cells (VSMCs), and development of proteinuria and renal injury. FHH rats exhibited poor autoregulation of RBF, while FHH.1BN congenic strains with the 2.4-Mbp BN region exhibited nearly perfect autoregulation of RBF. The diameter of AF-art from FHH rats increased in response to pressure but decreased in congenic strains containing the 2.4-Mbp BN region. Protein excretion and glomerular and interstitial damage were significantly higher in FHH rats than in congenic strains containing the 2.4-Mbp BN region. K(+) channel current was fivefold greater in VSMCs from renal arterioles of FHH rats than cells obtained from congenic strains containing the 2.4-Mbp region. Sequence analysis of the known and predicted genes in the 2.4-Mbp region of FHH rats revealed amino acid-altering variants in the exons of three genes: Add3, Rbm20, and Soc-2. Quantitative PCR studies indicated that Mxi1 and Rbm20 were differentially expressed in the renal vasculature of FHH and FHH.1BN congenic strain F. These data indicate that transfer of this 2.4-Mbp region from BN to FHH rats restores the myogenic response of AF-art and autoregulation of RBF, decreases K(+) current, and slows the progression of proteinuria and renal injury.

Association of α-adducin and G-protein β3 genetic polymorphisms with hypertension: a meta-analysis of Chinese populations

Background

Mounting evidence has suggested that α-adducin and G-protein β3 (GNB3) genes are logical candidates for salt-sensitive hypertension. Some, but not all, studies have reported that α-adducin G460T and GNB3 C825T polymorphisms may influence the risk of the disease. To comprehensively address this issue, we performed a meta-analysis to evaluate the influence of these two polymorphisms on hypertension and potential biases in Chinese.

Methods

Data were analyzed using Stata (v11.0) and random-effects model was applied irrespective of between-studies heterogeneity, which was evaluated via subgroup and meta-regression analyses. Study quality was assessed in duplicate. Publication bias was weighed using Egger's test and funnel plot.

Results

36 study populations totaling 9042 hypertensive patients and 8399 controls were finally identified. Overall, in allelic/genotypic/dominant/recessive models, no significant association was identified for both G460T and C825T polymorphisms (P>0.05) and there was possible heterogeneity (I²>25%). Subgroup analyses by study design indicated that the magnitude of association in population-based studies was marginally significantly strengthened for α-adducin G460T allelic model (OR = 1.12; 95% CI: 1:00–1.25; P = 0.043). Moreover, subgroup analyses by geographic distribution indicated comparison of 825T with 825C yielded a marginally significant increased risk in southern Chinese only (OR = 1.48; 95% CI: 1.01–2.16; P = 0.045). Further meta-regression analyses showed that geographic regions were a significant source of between-study heterogeneity for both polymorphisms. There was a possibility of publication bias for G460T, but not for C825T.

Conclusions

Our overall results suggest null association of α-adducin G460T and GNB3 C825T polymorphisms with hypertension in Chinese but indicate local marginal significance of C825T, as a putative salt-sensitive switch, in southern Chinese.

Alpha-adducin polymorphism associated with increased risk of adverse cardiovascular outcomes: results from GENEtic Substudy of the INternational VErapamil SR-trandolapril STudy (INVEST-GENES)

BACKGROUND

The alpha-adducin (ADD1) Gly460Trp polymorphism has been associated with hypertension and response to diuretic therapy, but controversy exists.

METHODS

The present study was conducted to prospectively investigate the relationship among the ADD1 Gly460Trp polymorphism, diuretic use, and adverse cardiovascular outcomes among 5,979 patients with hypertensive coronary artery disease, who participated in the INVEST and provided genomic DNA. The primary outcome was defined as the first occurrence of nonfatal stroke, nonfatal myocardial infarction, or all-cause death. Secondary outcomes were the components of the primary outcome. Ancestry informative markers were used to control for population stratification.

RESULTS

In blacks, ADD1 variant carriers were at higher risk for a primary outcome event than wild-type homozygotes (adjusted hazard ratio 2.62, 95% CI 1.23-5.58, P = .012), with a similar trend in whites and Hispanics, albeit a smaller magnitude of effect (adjusted hazard ratio 1.43, 0.86-2.39 in Hispanics; 1.24, 0.90-1.71 in whites). Secondary outcome analysis showed that the all-cause death was driving the differences in primary outcomes by genotype. There was no interaction between the ADD1 polymorphism and diuretic use for either primary outcome or secondary outcomes.

CONCLUSIONS

In hypertensive patients with coronary artery disease, black ADD1 variant carriers showed a 2.6-fold excess risk for a primary outcome event and an 8-fold increase risk of death. White and Hispanic ADD1 variant carriers showed an increased but nonsignificant excess risk. However, the effect of diuretic use on risk of cardiovascular outcomes did not vary by ADD1 carrier status.

Angiotensin converting enzyme DD genotype is associated with hypertensive crisis

OBJECTIVE

The genetic background of hypertensive crisis is unknown. We examined the association of polymorphisms in genes involved in the renin-angiotensin-aldosterone-system with hypertensive crisis.

DESIGN

Population-based case-control study.

SETTING

Emergency department at a tertiary care university hospital.

PATIENTS

A total of 182 patients with essential hypertension who were admitted to an emergency department for treatment of hypertensive crisis and 182 age- and sex-matched healthy individuals.

INTERVENTIONS

None.

MEASUREMENTS

Analysis of polymorphisms in genes coding for angiotensinogen (AJT 704T-->C), angiotensin II receptor 1 (AGTR1 1166A-->C), renin (REN 2646G-->A), renin-binding protein (RENBP 61T-->C), alpha-adducin (ADD1 1378G-->T), beta-2-adrenergic receptor (ADRB2 46A-->G, 79C-->G), and angiotensin I converting enzyme (ACE I/D) was performed by polymerase chain reaction and restriction fragment length polymorphism analysis. MAIN RESULTS Among patients, the ACE I/D polymorphism showed a deviation from Hardy-Weinberg equilibrium (p =.01). In controls, all polymorphisms were in the Hardy-Weinberg equilibrium. The frequency of the DD genotype was increased in patients (n = 70, 38.5%) vs. controls (n = 51; 28.0%;p =.03; odds ratio, 1.61; 95% confidence interval, 1.03-2.50), which was due to the DD genotype in 40 male patients (44%) vs. 23 in male controls (25.3%;p =.004; odds ratio, 3.48; 95% confidence interval, 1.47-8.30). There were no differences in genotype distributions among other polymorphisms.

CONCLUSION

We demonstrate a possible association of the DD genotype with hypertensive crisis in men.

ADD1 460W allele associated with cardiovascular disease in hypertensive individuals

High blood pressure is a predictor of cardiovascular disease. Hence, genes contributing to essential hypertension may play a role in the etiology of cardiovascular disease. For this reason, we examined the association between the alpha-adducin (ADD1) G460W and G-protein beta3 subunit (GNB3) 825C>T polymorphisms and the prevalence of peripheral arterial disease (PAD) and incidence of coronary heart disease (CHD) in non-Hispanic whites from the Atherosclerosis Risk in Communities (ARIC) Study. PAD prevalence was defined by an ankle-brachial index, ie, the ratio of ankle systolic blood pressure to brachial artery systolic blood pressure, of </=0.90 for men and </=0.85 for women. CHD incidence was determined by following the ARIC cohort for a median of 5.3 years for potential coronary events. Stratified random samples of the ARIC cohort (n=703 and n=684) were used, respectively, as the comparison groups for the PAD (n=144) and incident CHD (n=408) cases. The GNB3 825T allele and the ADD1 460W allele were not significantly associated with prevalence of PAD or incidence of CHD. However, a test of the interaction between hypertension status and the ADD1 G460W polymorphism indicated that further evaluation of the ADD1 polymorphism in only hypertensive individuals was warranted. The ADD1 460W allele was significantly associated with PAD (odds ratio [OR]: 2.61, 95% CI, 1.27-5.37, P=0.01) and CHD (hazard rate ratio [HRR]: 2.30, 95% CI, 1.20-4.42, P=0.01) in hypertensive individuals after adjustment for multiple cardiovascular disease risk factors. An interaction with hypertension in the association between the ADD1 G460W polymorphism and cardiovascular disease merits further testing in additional populations.

G-protein beta3 subunit and alpha-adducin polymorphisms and risk of subclinical and clinical stroke

BACKGROUND AND PURPOSE

Essential hypertension is a significant risk factor for stroke. Genes contributing to interindividual variation in blood pressure levels and essential hypertension status may play a role in the etiology of stroke either through their effects on blood pressure levels or through separate pathways. For this reason, we sought to examine the association between the alpha-adducin (ADD1) G/W460 and G-protein beta3 subunit (GNbeta3) 825C/T polymorphisms and subclinical and clinical stroke in the Atherosclerosis Risk in Communities (ARIC) Study.

METHODS

Subclinical stroke was determined by cerebral MRI. Subclinical cerebral infarct cases (n=202) were compared with a stratified random sample (MRI-CRS) identified from individuals participating in the MRI examination (n=211). Incidence of clinical ischemic stroke was determined by following the ARIC cohort for an average of 7.2 years for potential cerebrovascular events; 231 validated clinical ischemic strokes were identified. A stratified random sample of the ARIC cohort (CRS) (n=984) was used as the comparison group for the clinical cases.

RESULTS

The frequency of the ADD1 W460 allele was determined for the subclinical cases (0.12), MRI-CRS (0.16), clinical cases (0.14), and CRS (0.17). The frequency of the GNbeta3 825T allele was determined in whites and blacks, respectively, for the subclinical cases (0.26, 0.73), MRI-CRS (0.31, 0.75), clinical cases (0.36, 0.72), and CRS (0.30, 0.72). The ADD1 W460 and GNbeta3 825T alleles were not significantly associated with subclinical stroke. The ADD1 W460 allele was also not a significant predictor of clinical stroke. The GNbeta3 825T allele was significantly associated with clinical stroke in whites after adjustment for age and sex (hazard rate ratio, 1.45; 95% CI, 1.05 to 2.00) and after further adjustment for multiple stroke risk factors (hazard rate ratio, 1.68; 95% CI, 1.18 to 2.41). The GNbeta3 825T allele was not significantly associated with clinical stroke in blacks for either adjustment model.

CONCLUSIONS

The GNbeta3 gene 825C/T polymorphism is significantly associated with incident clinical ischemic stroke in a white middle-aged American population, but not in blacks. This association does not appear to be mediated by established stroke risk factors, specifically blood pressure levels or hypertension status.

Linkage analysis of candidate genes and gene-gene interactions in chinese hypertensive sib pairs

Previous studies of hypertension in humans and experimental animal models have identified a number of candidate genes that have since been implicated as possibly contributing to essential hypertension. Among them are the genes encoding angiotensinogen, renin, the beta- and gamma-subunits of the epithelial sodium channel (beta/gamma-ENaC), alpha-adducin, and kallikrein (KLK). To examine the role of possible contribution of these genes in ethnic Chinese, as well as the epistatic interaction among them, we studied a large cohort of hypertensive sib pairs from China. DNA samples from 310 concordant affected sibling pairs with hypertension were tested for linkage with the use of excess allele-sharing algorithms based on genotyping with highly informative GT-repeat microsatellite markers localized in the immediate vicinity of the genes encoding angiotensinogen, renin, beta- and gamma-ENaC, alpha-adducin, and KLK. Affected sib pair analysis conducted according to 3 different methods (Statistical Analysis for Genetic Epidemiology [S.A.G.E. ]/SIBPAL, MAPMAKER/SIBS, and affected pedigree member [APM] methods) revealed no evidence for linkage of any of these genes to primary hypertension in the population studied. Moreover, 2-locus sib pair linkage analyses to test for gene-gene interactions among each possible pair of candidate genes failed to yield any statistically significant results. Our findings provide no support for a significant contribution of the angiotensinogen, renin, beta/gamma-ENaC, alpha-adducin, or KLK genes, alone or in concert, to the pathogenesis of essential hypertension among Chinese. Our results emphasize the possible role of ethnic differences for complex disease genetics, as well as the need for large, well-characterized investigations.

Seven lessons from two candidate genes in human essential hypertension: angiotensinogen and epithelial sodium channel

The candidate gene approach to understanding the genetics of human essential hypertension is discussed by analyzing the contribution of 2 genes, angiotensinogen (AGT) and epithelial amiloride-sensitive sodium channel (ENaC). From a large series of studies conducted in humans and animals, it appears that the AGT gene plays a significant but modest role in human blood pressure variance. Mutations of the beta- and gamma-ENaC subunits are responsible for Liddle's syndrome, but the implication of the 3 ENaC subunits in essential hypertension is still questionable. Several lessons can be learned from these studies and applied to other candidate genes in essential hypertension: (1) Many linkage or association studies have a limited statistical power; (2) The genetic findings may vary greatly according to the populations studied; (3) There is a need for better phenotyping of the hypertensive population; (4) The causal relationship between molecular variants and hypertension is and will be difficult to establish firmly; (5) The contribution of genetic studied in rodents to the molecular genetics of human hypertension must be re-examined; (6) Most molecular variants lead to a low attributable risk in the population or a low individual effect at the individual level; and (7) It is too early to propose dietary recommendations and specific drug treatment according to patients' genotypes.

Use of animal models to search for candidate genes associated with essential hypertension

The use of inbred genetically hypertensive animal models enables the dissection of the underlying complex genetic traits into its individual components, and thus the elucidation and characterization of causative genes and gene variants. In addition, genetically hypertensive animal models will also be useful for the investigation of genetic characteristics that influence the effectiveness of antihypertensive therapy with specific pharmacologic agents. This report will discuss three different strategies that have recently been used for the identification of candidate gene loci or candidate genes for hypertension. The possibility to transfer of genetic data derived in animal models to human hypertension will also be considered.

Cardiac genes and gene databases for cardiovascular disease genetics

Genes play a very important role in the etiology of hypertension. This paper reviews the current pool of candidate genes for human hypertension. Some of the genes studied in rat models of hypertension are also discussed. The methods for studying the genetics of hypertension are reviewed. A discussion of the role of cardiac gene libraries and gene databases in the characterization of cardiovascular disease is also included. This review is concluded by a discussion on the future role of genomics and cardiovascular gene databases in medical research.

Genomics and hypertension: concepts, potentials, and opportunities

We are at the beginning of a biological revolution, spurred on by the Human Genome Project and associated studies. Within the next few years, expressed sequence tags (ESTs) representing all sequences expressed in humans will be determined and their genomic positions will be defined (STSs). The discovery of all the variants in the human genome that contribute to the genetic diversity of the human population will result in the construction of dense polymorphic maps. The rapid growth of the EST, STS, and single-nucleotide polymorphism (SNP) databases, coupled with impressive technological advances, will surely have a dramatic effect on biomedical research. In this review, we will examine the recent advances in genetics and genomics and place these within the context of medical research and patient care, with an emphasis on studies in the cardiovascular system.