No association between alpha-adducin 460 polymorphism and essential hypertension in a Japanese population

The Association between Gly460Trp-Polymorphism of Alpha-Adducin 1 Gene (ADD1) and Arterial Hypertension Development in Ukrainian Population

Arterial hypertension (AH) belongs to the diseases with genetic predisposition that determines the necessity of research on the genetic component's influence on this disease development. It is suggested that one of the salt-sensitive arterial hypertension potential markers may be the alpha-adducin gene because its protein product is involved in the ion transport regulation in the renal epithelium. Thus, the aim of the study was to investigate the association between ADD1 Gly460Trp-polymorphism and the AH development risk among patients with different risk factors in the Ukrainian population. The study included 232 Ukrainians: 120 patients with diagnosed arterial hypertension and 112 practically healthy individuals. Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis was used for ADD1 Gly460Trp-polymorphism genotyping. The ADD1 Gly460Trp-polymorphic locus is an important predictor of arterial hypertension development in the Ukrainian population, but other nongenetic factors should be considered in further studies.

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.

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.

Relationship between ADD1 Gly460Trp gene polymorphism and essential hypertension in Madeira Island

Essential hypertension (EH) is a complex disease in which physiological, environmental, and genetic factors are involved in its genesis. The genetic variant of the alpha-adducin gene (ADD1) has been described as a risk factor for EH, but with controversial results.The objective of this study was to evaluate the association of ADD1 (Gly460Trp) gene polymorphism with the EH risk in a population from Madeira Island.A case-control study with 1614 individuals of Caucasian origin was performed, including 817 individuals with EH and 797 controls. Cases and controls were matched for sex and age, by frequency-matching method. All participants collected blood for biochemical and genotypic analysis for the Gly460Trp polymorphism. We further investigated which variables were independently associated to EH, and, consequently, analyzed their interactions.In our study, we found a significant association between the ADD1 gene polymorphism and EH (odds ratio 2.484, P = .01). This association remained statistically significant after the multivariate analysis (odds ratio 2.548, P = .02).The ADD1 Gly460Trp gene polymorphism is significantly and independently associated with EH risk in our population. The knowledge of genetic polymorphisms associated with EH is of paramount importance because it leads to a better understanding of the etiology and pathophysiology of this pathology.

Association of alpha-ADD1 Gene and Hypertension Risk: A Meta-Analysis

Background

Results regarding the association between α-adducin (ADD1) gene and essential hypertension (EH) risk remain inconsistent. Therefore, we performed this meta-analysis to investigate this association.

Material/Methods

We comprehensively searched published literature from PubMed and Embase. All studies analyzing the association between ADD1 Gly460Trp polymorphism and EH risk were included. Fixed- or random-effects model was used to calculate pooled odds ratio (OR) with 95% confidence interval (CI).

Results

Data synthesis showed an increased risk of EH in T allele variant carriers with Asian descent, for GG vs. TT (OR=0.750, 95%CI: 0.585–0.960; P=0.022), recessive model (OR=1.196, 95%CI: 1.009–1.418; P=0.039), dominant model (OR=0.826, 95%CI: 0.693–0.985; P=0.033), and allelic model (OR=0.859, 95%CI: 0.756–0.964; P=0.01), respectively. However, no statistical differences were observed in Blacks and Caucasians.

Conclusions

The findings showed the association of the T allele in ADD1 gene with EH susceptibility in Asians. However, well-designed studies involving gene-gene and gene-environment interactions should be considered in future.

Gly460Trp polymorphism of the ADD1 gene and essential hypertension in an Indian population: A meta-analysis on hypertension risk

BACKGROUND:

Essential hypertension is a complex genetic trait. Genetic variant of alpha adducin (ADD1) gene have been implicated as a risk factor for hypertension. Given its clinical significance, we investigated the association between ADD1 Gly460Trp gene polymorphism and essential hypertension in an Indian population. Further, a meta-analysis was carried out to estimate the risk of hypertension.

METHODS:

In the current study, 432 hypertensive cases and 461 healthy controls were genotyped for the Gly460Trp ADD1 gene polymorphism. Genotyping was determined by real time PCR using Taqman assay. Multiple logistic regression analysis was used to detect the association between Gly460Trp polymorphism and hypertension.

RESULTS:

No significant association was found in the genotype and allele distribution of Gly460Trp polymorphism with hypertension in our study. A total of 15 case-control studies were included in the meta-analysis. There was no evidence of the association of Gly460Trp polymorphism with hypertension in general or in any of the sub group.

CONCLUSIONS:

We found that the Gly460Trp polymorphism is not a risk factor for essential hypertension in a south Indian Tamilian population. However, the role of ADD1 polymorphism may not be excluded by a negative association study. Further, large and rigorous case-control studies that investigate gene–gene–environment interactions may generate more conclusive claims about the molecular genetics of hypertension.

Alpha-adducin Gly460Trp polymorphism and hypertension risk: a meta-analysis of 22 studies including 14303 cases and 15961 controls

Background

No clear consensus has been reached on the alpha-adducin polymorphism (Gly460Trp) and essential hypertension risk. We performed a meta-analysis in an effort to systematically summarize the possible association.

Methodology/Principal Findings

Studies were identified by searching MEDLINE and EMBASE databases complemented with perusal of bibliographies of retrieved articles and correspondence with original authors. The fixed-effects model and the random-effects model were applied for dichotomous outcomes to combine the results of the individual studies. We selected 22 studies that met the inclusion criteria including a total of 14303 hypertensive patients and 15961 normotensive controls. Overall, the 460Trp allele showed no statistically significant association with hypertension risk compared to Gly460 allele (P = 0.69, OR = 1.02, 95% CI 0.94–1.10, P_{heterogeneity}<0.0001) in all subjects. Meta-analysis under other genetic contrasts still did not reveal any significant association in all subjects, Caucasians, East Asians and others. The results were similar but heterogeneity did not persist when sensitivity analyses were limited to these studies.

Conclusions/Significance

Our meta-analysis failed to provide evidence for the genetic association of α-adducin gene Gly460Trp polymorphism with hypertension. Further studies investigating the effect of genetic networks, environmental factors, individual biological characteristics and their mutual interactions are needed to elucidate the possible mechanism for hypertension in humans.

Association between alpha-adducin gene polymorphism (Gly460Trp) and genetic predisposition to salt sensitivity: a meta-analysis

Linkage and association studies suggested the relationship between alpha-adducin polymorphism (Gly460Trp; rs4961) and genetic susceptibility to salt-sensitivity. However, the currently available results were inconsistent. This study aimed to define quantitatively the association between salt-sensitivity and alpha-adducin Gly460Trp polymorphism in all published case-control studies. Publications from PubMed and other databases were retrieved. The major inclusion criteria were: (1) case-control design; (2) salt-sensitivity confirmed by sodium loading tests, and (3) the distribution of genotypes given in detail. Seven case-control studies fulfilled the inclusion criteria. In total they involved 820 subjects (454 salt-sensitive and 366 non-salt-sensitive). The meta-analysis shows that Gly460Trp polymorphism in general is not significantly associated with salt-sensitivity [OR (95%CI): 1.40 (0.96, 2.04), P = 0.08]. Subgroup analysis showed that the association is statistically significant in Asian people [OR (95%CI):1.33 (1.06, 1.69), P = 0.02] but not in Caucasian people [OR (95%CI):1.98 (0.57, 6.92), P = 0.28]. This indicates that blood pressure response to sodium varies between ethnical groups. More studies based on a larger population are required to evaluate further the role of alpha-adducin Gly460Trp polymorphism in salt-sensitive hypertension.

Relevance of Genetics and Genomics for Prevention and Treatment of Cardiovascular Disease

Atherosclerotic cardiovascular disease (CVD) is a major health problem in the United States and around the world. Evidence accumulated over decades convincingly demonstrates that family history in a parent or a sibling is associated with atherosclerotic CVD, manifested as coronary heart disease, stroke, and/or peripheral arterial disease. Although there are several mendelian disorders that contribute to CVD, most common forms of CVD are believed to be multifactorial and to result from many genes, each with a relatively small effect working alone or in combination with modifier genes and/or environmental factors. The identification and the characterization of these genes and their modifiers would enhance prediction of CVD risk and improve prevention, treatment, and quality of care. This scientific statement describes the approaches researchers are using to advance understanding of the genetic basis of CVD and details the current state of knowledge regarding the genetics of myocardial infarction, atherosclerotic CVD, hypercholesterolemia, and hypertension. Current areas of interest and investigation--including gene-environment interaction, pharmacogenetics, and genetic counseling--are also discussed. The statement concludes with a list of specific recommendations intended to help incorporate usable knowledge into current clinical and public health practice, foster and guide future research, and prepare both researchers and practitioners for the changes likely to occur as molecular genetics moves from the laboratory to clinic.

Molecular mechanisms linking sodium to hypertension: report of a symposium

There is abundant clinical and epidemiologic data linking excess body sodium with hypertension. The mechanism(s) at the molecular level to explain this relationship are unknown. Recent studies by multiple investigators, have identified several ion transport mechanisms in the vascular wall that interact to control vascular tone and contractility. These new data include 1) biochemical, pharmacologic, and molecule structural studies, 2) experiments in transgenic and knockout mice, and 3) results in clinical hypertension. The overall results provide compelling evidence for the concept that salt-dependent hypertension involves the secretion of endogenous ouabain (EO), an adrenal steroid synthesized with the same initial steps as aldosterone and secreted by the zona glomerulosa. Circulating EO inhibits arterial smooth muscle Na+ pumps with alpha 2 subunits. These are functionally coupled to the type 1 Na/Ca exchanger (NCX1). Thus when a2 Na pumps are inhibited in arterial smooth muscle, the resulting subplasma membrane increase in Na+ concentration triggers, via NCX1 Ca2+ entry, a rise in cytosolic Ca2+ concentration and increased myogenic tone and contractility. The ultimate result is a rise in peripheral vascular resistance-the hemodynamic hallmark of hypertension. The elucidation of this pathway has facilitated the development of pharmacologic agents that have therapeutic potential for hypertension and other cardiovascular diseases. These include agents that compete with EO for binding to the Na+ pump and inhibitors of NCX1.

Genetic variations of tubular sodium reabsorption leading to “primary” hypertension: from gene polymorphism to clinical symptoms

The definition of the most appropriate strategy to demonstrate causation of a given genetic-molecular mechanism in a complex multifactorial polygenic disease like hypertension is hampered by the underestimation of the complexity arising from the genetic and environmental interactions. To disentangle this complexity, we developed a strategy based on six steps: 1) isolation of a rodent model of hypertension (Milan hypertensive strain and Milan normotensive strain) that shares some pathophysiological abnormalities with human primary hypertension; 2) definition in the model of the sequence of events linking these abnormalities to a genetic molecular mechanism; 3) determination of the polymorphism of the three adducin genes discovered in the model both in rats and in humans; 4) comparison at biochemical and physiological levels between the rodent models and the hypertensive carriers of the “mutated” gene variants; 5) evaluation of the impact of the adducin genes in hypertension and its organ complications with association and linkage studies in humans, also considering the genetic and environmental interactions; and 6) development of a pharmacogenomic approach aimed at establishing the therapeutic benefit of a drug interfering with the sequence of events triggered by adducin and their effect's size. The bulk of data obtained demonstrates the importance of a multidisciplinary approach considering a variety of genetic and environmental interactions. Adducin functions within the cells as a heterodimer composed of a combination of three subunits. Each of these subunits is coded by genes mapping to different chromosomes. Therefore, the interaction among these genes, taken together with the interactions with other modulatory genes or with the environment, is indispensable to establish the adducin clinical impact. The hypothesis that adducin polymorphism favors the development of hypertension via an increased tubular sodium reabsorption is well supported by a series of consistent experimental and clinical data. Many mechanistic aspects, underlying the link between these genes and clinical symptoms, need to be clarified. The clinical effect size of adducin must be established also with the contribution of pharmacogenomics with a drug that selectively interferes with the sequence of events triggered by the mutated adducin.

Associations of baseline blood pressure levels and efficacy of Benazepril treatment with interaction of alpha-adducin and ACE gene polymorphisms in hypertensives

The molecular mechanisms underlying essential hypertension are not fully elucidated. Although Benazepril is being widely used in antihypertensive medication, the agent is efficacious in only a portion of hypertensive patients. To evaluate the interaction of alpha-adducin gene Gly460Trp and angiotensin I-converting enzyme (ACE) gene I/D polymorphisms in regard to baseline blood pressure (BP) levels and the reductions of blood pressures after Benazepril treatment, we conducted an investigation of 954 Chinese hypertensive patients in Anhui province, China. We found that compared with the baseline systolic BP (SBP) of subjects with one ACE I allele and one alpha-adducin Trp allele, the baseline SBP of those with ACE DD and alpha-adducin Gly/Gly genotypes was significantly higher [Crude: beta(SE) = 7.83(3.09), p = .01; Adjusted: beta(SE) = 5.83(2.83), p = .04]. However, no associations were found between the interaction of ACE I/D and alpha-adducin Gly460Trp polymorphisms and the baseline diastolic BP or the BP response to Benazepril treatment. Our results suggested that the interaction effect of alpha-adducin Gly460Trp and ACE I/D polymorphisms might play a significant role in regulating baseline BP but not BP response to Benazepril.

Sodium-lithium countertransport and the Gly460-->Trp alpha-adducin polymorphism in essential hypertension

A polymorphism of the alpha-subunit of adducin, Gly460-->Trp, may affect membrane ion transport and be associated with human EH (essential hypertension). The alpha-adducin Gly460-->Trp polymorphism was determined in 242 NC (normal controls) and 73 patients with EH and was related to the membrane ion transport marker in EH, erythrocyte Na/LiCT (sodium-lithium countertransport), in a subgroup of these subjects. The Km for external sodium was lower in patients with EH than NC. The Km of the Trp allele was lower than with the Gly/Gly genotype [NC, 105+/-6 compared with 88+/-5 mmol Na/l respectively (P=0.05); patients with EH, 76+/-5 compared with 64+/-4 mmol Na/l respectively (P=0.06)]. The Km was lower in patients with EH than NC for any adducin genotype. Thiol alkylation with NEM (N-ethylmaleimide) caused a decrease in Km in NC, but not in patients with EH. With a Trp allele, NEM lowered Km less in NC (-20 compared with -35) and increased it in patients with EH (+24 compared with +3; P=0.007 for genotype effect). Thiol alkylation with NEM caused an increase in Vmax in patients with EH but not in NC. With a Trp allele, NEM increased Vmax substantially in patients with EH (+0.12 compared with +0.03) but did not cause a decrease in NC (+0.02 compared with -0.06; P=0.007 for genotype effect). In conclusion, the Gly460-->Trp polymorphism of alpha-adducin modifies the kinetics of Na/LiCT. The effect of this genotype is different in patients with EH compared with NC and it does not explain the abnormal kinetics in patients with EH. The Trp allele was not associated with disease in the population studied. Several cytoskeletal proteins may interact with adducin in the overall phenotype of EH.

Genetics of human hypertension

Hypertension is a complex genetic disorder caused by interplay between several "risk" genes and environmental factors (genetic heritability approximately 30%). Most genetic studies of hypertension use a candidate gene approach and two conclusions have been made: there is no association or linkage with the genes studied, or the hypertension phenotype is heterogeneous and subgroups with hypertension related to certain polymorphisms cannot be identified because of background noise. Studies using intermediate phenotypes suggest the latter is most likely. Another problem is the reliability of gene structure assessment: usually only one or two gene polymorphisms are assessed. The use of intermediate phenotypes and dense mapping of candidate genes would provide a better approach for identifying genotype-phenotype correlations, which might enable the use of genotypes to identify more-specific therapeutic and preventative measures for hypertensives.

Blood pressure in relation to three candidate genes in a Chinese population

OBJECTIVE

In a prospective analysis of a Caucasian population, we recently found that the genes encoding angiotensin-converting enzyme (ACE, I/D polymorphism), alpha-adducin (Gly460Trp) and aldosterone synthase (-344C/T) jointly influence the incidence of hypertension. We therefore investigated the association between blood pressure and these three genes in a Chinese population.

METHODS

We genotyped 479 Han Chinese from 125 nuclear families recruited in northern China via random sampling (approximately 75%) and at specialized hypertension clinics (approximately 25%). We performed population-based and family-based association analyses using generalized estimating equations (GEE) and the quantitative transmission disequilibrium test (QTDT), respectively, while controlling for covariables.

RESULTS

The participants included 239 (49.9%) women and 132 (27.6%) hypertensive patients, of whom 77 took antihypertensive drugs. The blood pressure, measured at the subjects' homes, averaged 126/80 mmHg. Mean values of urinary sodium, potassium and Na/K ratio were 226 mmol/day, 37 mmol/day and 6.31, respectively. In adjusted GEE analyses, systolic blood pressure was 9.3 mmHg (95% confidence interval 3.6-15.0 mmHg; P = 0.001) and 14.6 mmHg (95% confidence interval 3.4-25.8 mmHg; P = 0.01) higher in the ACE DD than II subjects among the alpha-adducin TrpTrp (n = 141) and aldosterone synthase CC (n = 33) homozygotes, respectively (P < or =0.05 for interactions of the ACE genotype with the alpha-adducin and aldosterone synthase polymorphisms). Among 40 informative offspring homozygous for the alpha-adducin Trp allele, systolic blood pressure was significantly associated with transmission of the ACE D allele (beta = 5.5 mmHg; P = 0.046).

CONCLUSIONS

The ACE I/D, alpha-adducin Gly460Trp and aldosterone synthase -344C/T polymorphisms interact to influence systolic blood pressure in Chinese, suggesting that these genes might indeed predispose to hypertension, especially in an ecogenetic context characterized by a high salt intake.

Alpha-adducin Gly460Trp polymorphism and essential hypertension in Korea

Previous studies have suggested that the Gly460Trp polymorphism of the alpha-adducin gene (ADD-1) is associated with salt sensitivity and primary hypertension. The results of linkage or association studies of ADD-1 of different populations are controversial. This study investigated the relationship between the Gly460Trp polymorphism of ADD-1 and essential hypertension in a Korean population. The subjects (n=903) were participants in a population-based study in Jangseong County, Korea. The Gly460Trp polymorphism of ADD-1 was determined using a polymerase chain reaction method. The frequency of the 460Trp allele was 59.4% in normotensives and 61.1% in hypertensives (p=0.523). The frequencies of the genotypes did not differ significantly between the hypertensive and normotensive groups (16.3% Gly/Gly, 45.8% Gly/Trp, and 38.0% Trp/Trp in normotensives; 16.2% Gly/Gly, 45.8% Gly/Trp, and 38.0% Trp/Trp in hypertensives; p=0.928). After adjusting for other risk factors, Gly/Trp and Trp/Trp were not associated with hypertension (OR 1.00, 95% CI 0.65-1.53, Gly/Trp vs. Gly/Gly; OR 1.22, 95% CI 0.79-1.90, Trp/Trp vs. Gly/Gly). These findings suggest that the Gly460Trp polymorphism of ADD-1 is not associated with hypertension.

Alpha-adducin gene polymorphism is associated with essential hypertension in Chinese: a case-control and family-based study

OBJECTIVE

A polymorphism at position 460(G <-- W) of the alpha-adducin gene was found to be associated with essential hypertension in some but not all studies. The aim of the present study was to further investigate the association of the alpha-adducin 460W allele with essential hypertension in Chinese population.

METHODS

Individuals from a population-based sample (n = 748) and 95 nuclear families and 47 discordant sibships were studied by questionnaire as well as by physical examination and biochemical analyses. The alpha-adducin gene G460W polymorphism was determined by polymerase chain reaction and restriction enzyme digestion. Chi-square test, one-way analysis of variance, logistic regression, linear regression, haplotype-based haplotype relative risk and transmission/disequilibrium test analyses were used to determine the association between the alpha-adducin G460W polymorphism and essential hypertension.

RESULTS

In the case-control study, the prevalence of hypertension was higher in individuals with the WW genotype (40.0%) as compared with those with the GW and GG genotype (31.7%) (chi2 = 4.768, P = 0.029, odds ratio = 1.43). Adjusted for the conventional risk factors of hypertension, alpha-adducin polymorphism still plays an independent role on systolic blood pressure. We confirmed the results of our case-control study by observing a significant preferential transmission of the 460W allele of the alpha-adducin to the affected subjects in another northern Chinese population (for haplotype-based haplotype relative risk, chi2 = 6.24, P = 0.01; and for the transmission/disequilibrium test, chi2 = 4.69, P = 0.03).

CONCLUSIONS

The present findings show a positive association between the alpha-adducin G460W polymorphism and essential hypertension in a northern Chinese population. This evidence indicates that the alpha-adducin gene may be a susceptible gene to essential hypertension.

Interaction between ACE and ADD1 gene polymorphisms in the progression of IgA nephropathy in Japanese patients

An interaction effect between the angiotensin-converting enzyme insertion/deletion (ACE I/D) and alpha-adducin (ADD1) Gly460Trp polymorphisms (G460W) on blood pressure regulation has recently been suggested, although its significance in the prognosis of renal function in IgA nephropathy (IgAN) has not been fully investigated. Therefore, we evaluated the clinical manifestations and renal prognosis in 276 Japanese patients with histologically proven IgAN with respect to their ACE I/D and ADD1 G460W polymorphisms. The prognosis of renal function was analyzed by Kaplan-Meier survival curves and multivariate Cox proportional-hazards regression models. Baseline data, including blood pressures, proteinuria, renal function, and incidence of hypertension, were similar for the different genotypes of ACE and ADD1. The individual genotypes taken alone were not associated with the progression of renal dysfunction. However, renal survival of patients with the 460WW polymorphism of ADD1 was significantly worse within the group with the II genotype of ACE (Kaplan-Meier, log rank test; chi2=6.062, P=0.0138) but not for those with other ACE genotypes. In the Cox proportional-hazards regression model with adjustment for clinical risk factors, including hypertension, proteinuria, and no administration of an angiotensin-converting enzyme inhibitors or angiotensin II receptor blockers, the 460WW variant of ADD1 was a highly significant and independent risk factor only for patients with the ACE II genotype, with a hazard ratio of 3.65 (P=0.0016), but not for those with other ACE genotypes (hazard ratio=0.65, P=0.2902). These findings suggest an interaction between ACE and ADD1 polymorphisms not only on blood pressure regulation but also on the progression of renal dysfunction in patients with IgAN.

Problems of reporting genetic associations with complex outcomes

Inability to replicate many results has led to increasing scepticism about the value of simple association study designs for detection of genetic variants contributing to common complex traits. Much attention has been drawn to the problems that might, in theory, bedevil this approach, including confounding from population structure, misclassification of outcome, and allelic heterogeneity. Other researchers have argued that absence of replication may indicate true heterogeneity in gene-disease associations. We suggest that the most important factors underlying inability to replicate these associations are publication bias, failure to attribute results to chance, and inadequate sample sizes, problems that are all rectifiable. Without changes to present practice, we risk wastage of scientific effort and rejection of a potentially useful research strategy.

Association between hypertension and variation in the alpha- and beta-adducin genes in a white population

BACKGROUND

The substitution of tryptophan for glycine at amino acid 460 (Gly460Trp polymorphism) of the alpha-subunit of the heterodimeric cytoskeleton protein adducin increases renal sodium reabsorption and may be involved in the pathophysiology of essential hypertension. In the present study, we investigated in multivariate analyses whether the risk of hypertension was associated with the C1797T polymorphism of the beta-adducin gene.

METHODS

A total of 1848 subjects randomly selected from a white population were genotyped. Study nurses measured blood pressure at the participants' homes.

RESULTS

The frequencies of the alpha-adducin Trp and beta-adducin T alleles were 0.23 and 0.11, respectively. In men (N = 904), the beta-adducin T allele was not associated with hypertension [adjusted relative risk (RR) vs. CC homozygotes 0.94, P = 0.77], but T allele carriers had lower plasma renin activity (PRA) and 24-hour urinary aldosterone excretion (P < 0.04). In all women (N = 944), beta-adducin T allele carriers had a higher risk of hypertension than CC homozygotes (RR 1.81, CI 1.18-2.77, P = 0.007), but similar PRA and 24-hour urinary aldosterone excretion (P> 0.29). In 345 post-menopausal women and 190 users of oral contraceptives, the RRs of hypertension were 2.47 (CI 1.34-4.64, P = 0.003) and 2.56 (CI 0.83-7.86, P = 0.10), respectively. For systolic pressure in women, there was a significant interaction (P = 0.02) between the alpha- and beta-adducin polymorphisms. Only in female carriers of the mutated alpha-adducin Trp allele was the systolic pressure significantly higher in beta-adducin T allele carriers compared with CC homozygotes (+3.8 mm Hg, P = 0.02). Furthermore, in the presence of the mutated alpha-adducin Trp allele, the RRs associated with the beta-adducin T allele were 2.35 (P = 0.01) in all women, 2.92 (P = 0.03) in post-menopausal subjects, and 3.79 (P = 0.09) in users of oral contraceptives.

CONCLUSIONS

The 1797T allele of the beta-adducin gene is associated with increased risk of hypertension in post-menopausal women and in users of oral contraceptives, particularly in the presence of the mutated alpha-adducin Trp allele. We hypothesize that inhibition of the renin-aldosterone system in men and absence of such a compensatory mechanism in women may explain, at least to some extent, the sexual dimorphism of the blood pressure phenotype in relation to the C1797T beta-adducin polymorphism.

alpha-Adducin Gly460Trp polymorphism is associated with low renin hypertension in younger subjects in the Ohasama study

BACKGROUND

The Gly460Trp polymorphism of the alpha-adducin gene (ADD-1 ) has been examined as a candidate gene for essential hypertension with salt sensitivity in the Caucasian population. However, we failed to detect a positive association between the Gly460Trp polymorphism of ADD-1 and hypertension in a small series of Japanese subjects.

OBJECTIVE

To examine the precise association between the Gly460Trp polymorphism of ADD-1 and blood pressure (BP), we carried out an association study using a Japanese population: the Ohasama Study.

DESIGN

Subjects (n = 1490) were recruited from participants in the Ohasama Study, which is a cohort in a rural community of northern Japan.

METHODS

DNA was extracted from the buffy coat of the participants who gave informed consent for genetic analysis, and the Gly460Trp polymorphism of ADD-1 was determined by the TaqMan polymerase chain reaction method. Various BP values (casual BP, ambulatory BP and home BP) were measured in the Ohasama study. We used the mean values of these BP measurements for analysis.

RESULTS

The frequencies of genotypes in the Ohasama population were 23% Gly/Gly, 49% Gly/Trp, and 28% Trp/Trp. In the baseline characteristics, age, sex, body mass index, frequency of diabetes and hyperlipidemia were significantly different between hypertensive or normotensive subjects. In total subjects, all BP values were not different among genotypes. In the younger subjects ( 60 years old) with low plasma renin activity (< 1.0 ng/ml per h), however, ambulatory BP and home BP were significantly higher in the subjects with the Gly/Trp or Trp/Trp genotypes of ADD-1 polymorphism than in those with the Gly/Gly genotype. In the same population, the frequency of the Gly/Trp or Trp/Trp genotypes of was significantly higher in hypertensives than in normotensives (83 versus 72%, chi1(2) = 4.04, P<0.05; odds ratio, 2.12; 95% confidence interval, 1.02-4.68).

CONCLUSIONS

These findings suggest the possibility that the Gly460Trp polymorphism of ADD-1 is associated with low renin hypertension.

Linkage analysis of twelve candidate gene loci regulating water and sodium metabolism and membrane ion transport in essential hypertension

To investigate the relationship between 12 candidate genes responsible for water regulation, sodium metabolism and membrane ion transport and essential hypertension (EH) in the Chinese. Linkage analysis of EH was performed in 95 Chinese nuclear families including 477 subjects using a technique of fluorescence-based gene scanning with 12 microsatellite markers. Markers were selected on the chromosomal regions covering 12 candidate genes responsible for regulating water and sodium metabolism and membrane ion transport. These candidate genes included sodium hydrogen exchanger 3, sodium hydrogen exchanger 5, chloride bicarbonate exchanger 3, sodium calcium exchanger 1, mineralocorticoid receptor, plasma membrane calcium ATPase 2, ATPase,Na/K transporting alpha, a-adducin, SA gene, kidney epithelial sodium channel-gamma, vasopressin receptor 1A, and 11beta-hydroxysteroid dehydrogenase type 2 genes. Two-point non-parametric linkage analysis (NPL), maximum LOD score analysis and transmission/disequilibrium test (TDT) were performed using the GENEHUNTER software package. The NPL analysis and LOD score suggested a significant linkage at D12S398 (Z = 2.08, p<0.05 and LOD score = 1.26, p<0.01, respectively). TDT indicated a significant disequilibrium of transmission at the locus chi2 = 9.00, p < 0.005). No significant linkages were found at the other loci tested (p > 0.05 or LOD < -1). In conclusion, D12S398, a marker near the vasopressin receptor 1A gene (V1AR), showed a positive linkage with EH based on the results of three statistical methods (NPL, LOD score, and TDT). This region warrants further exploration.

Role of the alpha-adducin genotype on renal disease progression

BACKGROUND

A genetic susceptibility to hypertension may predispose to the development of end-stage renal disease (ESRD) and promote a more rapid loss of renal function in patients with renal diseases. The alpha-adducin (ADD) gene, alone or in combination with the angiotensinogen (AGT) and the angiotensin-converting enzyme (ACE), is a candidate for abnormal blood pressure regulation and thus for increased susceptibility or faster progression to ESRD.

METHODS

Genotyping for the G460W-ADD, M235T-AGT and the insertion/deletion (I/D)-ACE gene polymorphisms was performed in 260 control subjects and 260 ESRD patients using polymerase chain reaction, gel analysis and appropriate restriction digest.

RESULTS

The frequencies of the ADD, AGT and ACE genotypes in ESRD patients did not differ from observed frequencies in control subjects. The average (+/-SE) time from diagnosis to the onset of ESRD tended to be shorter in the presence of the ADD-460WW (5.1 +/- 1.1 years, N = 10) than with the GW (9.9 +/- 0.7 years, N = 81) and GG (11.3 +/- 1.0 years, N = 164) genotypes (F-ratio=2.71, P = 0.068; WW vs. GW P < 0.06 and vs. GG <0.03). In the 167 patients homozygous for the ADD-G allele, a more rapid progression with the ACE-DD genotype as compared to ACE-DI and II was found (P < 0.02).

CONCLUSIONS

The ADD genotype is predictive of the course of renal function loss in an unselected renal population and influences the effect of the ACE genotype to modulate the rate of progression to ESRD. Thus, the ADD genotype may play a role for the understanding of interindividual differences in the course of renal diseases.

Low-renin hypertension, altered sodium homeostasis, and an alpha-adducin polymorphism

Defining the genetic basis of common forms of human essential hypertension is most informative when correlated with physiological mechanisms that underlie blood pressure regulation. A polymorphism of the alpha-adducin gene as been associated with elevated blood pressure in the rat, but previous studies of the 460Trp polymorphism of the human alpha-adducin gene have not clearly identified an association with hypertension. In this study, the frequency of the 460Trp allele was 19% and 9 of 279 subjects (3.2%) were homozygous for the 460Trp allele. The systolic blood pressure response to changes in dietary sodium was significantly greater in subjects homozygous for the 460Trp allele (25 +/- 4 mm Hg) compared with subjects heterozygous for 460Trp (12 +/- 2 mm Hg) or homozygous for the 460Gly allele (14 +/- 1 mm Hg). Intracellular erythrocyte sodium content, sodium-lithium countertransport, and renal fractional excretion of sodium were significantly decreased in subjects homozygous for the 460Trp polymorphism (P<0.05). There was a significant association between homozygosity for the 460Trp allele and low-renin hypertension. Subjects heterozygous for the 460Trp allele did not have increased salt-sensitivity or an increased frequency of low-renin hypertension. Therefore, this study demonstrates a common genetic basis for altered cellular sodium homeostasis, impaired renal sodium handling, and salt-sensitivity of systolic blood pressure in individuals homozygous for the 460Trp polymorphism of the alpha-adducin gene. Homozygosity for this alpha-adducin allele may be an important determinant for approximately 10% of individuals with low-renin hypertension.

alpha-Adducin gene and essential hypertension in China

Adducin is a membrane skeletal protein that is involved in the regulation of membrane ion transport and cellular signal transduction. Essential hypertension has been linked to alpha-adducin gene locus, and association of a polymorphism of the gene has been found in some studies, but results of linkage or association studies on alpha-adducin gene are controversial among different populations. This study was designed to examine the linkage between alpha-adducin gene locus and essential hypertension and to reveal the relationship between an alpha-adducin gene polymorphism (Gly460Trp) and essential hypertension in a Chinese population. For the linkage study, one hundred and six Chinese nuclear families were recruited, including 417 hypertensive patients in all 474 individuals. Those samples were genotyped at D4S412 and D4S3038. The distances between the two microsatellite markers and the alpha-adducin gene locus are less than 3cM. Parametric, non-parametric linkage (NPL) analyses using the GENEHUNTER software were carried out. Sib transmission-dise- quilibrium test (S-TDT), as well as transmission-disequilibrium test (TDT). was also implemented with TDT/S-TDT Program 1.1. Serum levels of uric acid, creatinine, blood urea nitrogen (BUN), fasting glucose and lipids were determined as phenotypes. In an association study, 138 hypertensive and 121 normotensive subjects were genotyped at Gly460Trp of the alpha-adducin gene to examine a possible association between this polymorphism and blood pressure or other phenotypes. We fail to find the linkage between the two markers and essential hypertension by parametric, NPL analysis or TDT/S-TDT study. With the use of the simple association and the multivariate logistic regression analyses, we also fail to reveal a significant association between the Gly460Trp polymorphism in alpha-adducin gene and the blood pressure variation, or blood biochemical indices studied. The frequency of the 460Trp allele in Chinese (46-48%) is similar to that found in Japanese (54-60%) while the allele frequency is less common in Caucasian (13%-23%). These findings suggest that in our Chinese population, alpha-adducin 460Trp variant may not play an important role in the etiology of EH. And the negative results of linkage and TDT/ S-TDT further supports this conclusion.

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.

Genetic mapping of blood pressure quantitative trait loci in Milan hypertensive rats

In a previous study, by using a candidate gene approach, we detected in both Milan hypertensive rats and humans a polymorphism in the alpha-adducin gene (ADD1) that was associated with blood pressure and renal sodium handling. In the present study, a genomewide search with 264 informative markers was undertaken in 251 (Milan hypertensive strain x Milan normotensive strain) F2 rats to further investigate the contribution of the adducin gene family (Add1, Add2, and Add3) and to identify novel quantitative trait loci (QTLs) that affect blood pressure. The influence of 2 different methods of blood pressure measurement, the intracarotid catheter and the tail-cuff method, was also evaluated. We found evidence that QTLs affected systolic blood pressure (SBP) measured at the carotid (direct SBP) on rat chromosome 1 with a logarithm of the odds (LOD) score peak of 3.3 on D1Rat121 and on rat chromosome 14 on Add1 locus (LOD=3.2). A QTL for SBP measured at the tail (indirect SBP) was found on rat chromosome 10 around D10Rat33 (LOD=5.0). All of these QTLs identified chromosomal regions not detected in other rat studies and harbor genes (Na(+)/H(+) exchanger A3; alpha-adducin; alpha(1B)-adrenergic receptor) that may be involved in blood pressure regulation. Therefore, these findings may be relevant to human hypertension, also in consideration of the biochemical and pathophysiological similarities between MHS and a subgroup of patients of primary hypertension, which led to the identification of alpha-adducin as a candidate gene in both species.

Hypertension in beta-adducin-deficient mice

Polymorphic variants of the cytoskeletal protein adducin have been associated with hypertension in humans and rats. However, the direct role of this protein in modulating arterial blood pressure has never been demonstrated. To assess the effect of beta-adducin on blood pressure, a beta-adducin-deficient mouse strain (-/-) was studied and compared with wild-type controls (+/+). Aortic blood pressure was measured in nonanesthetized, freely moving animals with the use of telemetry implants. It is important to note that these mice have at least 98% of C57Bl/6 genetic background, with the only difference from wild-type animals being the beta-adducin mutation. We found statistically significant higher levels of systolic blood pressure (mm Hg) (mean+/-SE values: -/-: 126.94+/-1.14, n=5; +/+: 108.06+/-2. 34, n=6; P:</=0.0001), diastolic blood pressure (-/-: 83.54+/-1.07; +/+: 74.87+/-2.23; P:</=0.005), and pulse blood pressure (-/-: 43. 32+/-1.10; +/+: 33.19+/-1.96; P:</=0.001) in beta-adducin-deficient mice. Western blot analysis showed that as a result of the introduced genetic modification, beta-adducin was not present in heart protein extracts from -/- mice. Consequently, this deficiency produced a sharp decrease of alpha-adducin and a lesser reduction in gamma-adducin levels. However, we found neither cardiac remodeling nor modification of the heart function in these animals. This is the first report showing direct evidence that hypertension is triggered by a mutation in the adducin gene family.

Lack of association of 3 functional gene variants with hypertension in African Americans

African Americans are a critical population in which to study the impact of physiologically important candidate gene mutations on the occurrence of hypertension. African Americans not only have a higher prevalence of hypertension, but the disease strikes earlier, with greater severity, and often results in death at an earlier age compared with whites in the United States. In this study, 3 physiologically important candidate gene mutations (angiotensinogen A[-6], alpha-Adducin Gly460Trp, and G-Protein beta(3)-subunit C825T) were examined for their association with hypertension status in a sample of 904 African Americans from Jackson, Mississippi. Tests of simple association and multivariate logistic regression analyses revealed no association between hypertension status and any of the studied polymorphisms. This lack of association persisted after stratification of the sample by gender and body size. These data indicate that these polymorphisms do not contribute in a significant way to interindividual variation in the risk of hypertension in this sample of African Americans, and further genome-wide studies should be performed to identify genes that may influence blood pressure levels in this population.

Lack of evidence for an association between alpha-adducin and blood pressure regulation in Asian populations

Recent studies have found the tryptophan allele of a glycine to tryptophan polymorphism at position 460 (G460W) of the alpha-adducin protein to be associated with essential hypertension in European populations. We examined whether the tryptophan allele is associated with hypertension in a different population, comprised of subjects of Chinese origin from Taiwan, and Chinese and Japanese origin from the San Francisco Bay area and Hawaii. We adapted the 5' allelic discrimination assay or TaqMan to type individuals for the G460W polymorphism, and using this method we typed more than 1000 individuals. The frequency of the W allele was slightly increased in the treated subjects in the Chinese population (0.458 v 0.423) but not the Japanese population (0.549 v 0.558). We considered dominant, recessive, and additive models in our analysis. There was a significant result for a recessive model for systolic blood pressure in the Chinese population (chi2 6.84, df = 2, P < .05), but only suggestive evidence for diastolic blood pressure (chi2 3.30). In contrast, in the Japanese population, there was no evidence for a positive association under any model. For the combined Chinese and Japanese samples, the evidence for association with alpha-adducin was not significant.

Association and linkage analysis of the alpha-adducin gene and blood pressure

In Milan hypertensive rats, a variant in the alpha-adducin gene has been shown to account for approximately 50% of the interindividual variation in blood pressure levels between these animals and their normotensive counterparts. Additional studies have suggested that a polymorphism within exon 10 of the human alpha-adducin gene (Gly-460-Trp) may be associated with hypertension and salt sensitivity. On the basis of these observations, we investigated variation within or near the human alpha-adducin gene for linkage and association with a locus influencing blood pressure levels in 281 nuclear families (774 siblings aged 5 to 37 years; 380 parents aged 26 to 57 years), selected from the white population of Rochester, Minnesota, without regard to health. Sib pair linkage analyses (n = 852 sibling pairs) using a dinucleotide repeat marker (D4S43) that maps approximately 660 kb from the alpha-adducin gene provided no evidence of linkage between this marker locus and a locus influencing systolic, diastolic, or mean blood pressure levels. Allele frequencies for the Gly-460-Trp polymorphism were similar to those reported in other white populations (Gly = 0.812, Trp = 0.188); however, this polymorphism was not associated with any measure of blood pressure level in either parents or siblings. Therefore, variation within the alpha-adducin gene does not appear to have a major influence on measures of blood pressure in white families from Rochester, Minnesota.

Alpha-adducin polymorphism in hypertensives of South African ancestry

The alpha-adducin gene contributes significantly to hypertension in MHS rats (rats of the Milan hypertensive strain) and in some white and Japanese populations, causing a low renin, sodium, and diuretic-sensitive hypertension. No data are available from populations of African ancestry who have a high prevalence of low renin, sodium, and diuretic-sensitive hypertension. We studied the relationship between the 460-Trp variant of alpha-adducin gene with hypertension using a case-control study design in black South Africans. Surprisingly we found that the overall frequency of the 460-Trp allele was low (approximately 6%), but in spite of such relatively low frequency, the 460-Trp allele was 2.5-fold more frequent in hypertensives than normotensives (P = .028), with an odds ratio for hypertension associated to the state of carrier of at least one 460-Trp allele of 2.68. The finding of such low frequency of the 460-Trp allele in individuals of African ancestry points to the substantial ethnic variability of the genes that have been found to be associated with hypertension. On the other hand, it suggests an association of the 460-Trp allele with hypertension also in subjects of African origin.

The genomics of cardiovascular disorders: therapeutic implications

Cardiovascular disease (CVD) is a complicated series of disorders that result from the interaction between genetic predisposing mechanisms and environmental factors. Over the last few years substantial progress has been made in defining the molecular basis of several genetically transmitted non-atherosclerotic CVD such as hypertrophic and dilated cardiomyopathies, long-QT syndrome and essential hypertension. This review represents a summary of the current knowledge about the major gene polymorphisms found to be associated with these CVDs. Moreover, we will discuss how the discovery of disease-associated genes will greatly enhance the ability to formulate advanced diagnoses, to define prophylactic therapeutic strategies to prevent or reduce the progression of the disease and, finally, to proceed to the development of new drugs tailored for the specific cellular or molecular functions altered as consequence of the predisposing genes.

Renal proximal tubule sodium transport and genetic mechanisms of essential hypertension

Renal sodium re-absorption is a closely regulated process serving to maintain both extracellular fluid volume and arterial blood pressure. Proteins participating in sodium re-absorption and its regulation are therefore important candidate proteins whose genes may contain sequence variation contributing to the inherited tendency for increased arterial blood pressure (essential hypertension). Important insight has come from rare forms of single-gene hypertension in human subjects and from polygenic animal models of genetic hypertension. Both indicate the primacy of altered renal function in the genesis of hypertension, and suggest that genes contributing to the disease are members of the subset of genes expressed in the kidney. This review examines evidence for abnormalities in renal sodium re-absorption in hypertension and focuses on the proximal tubule as a site of relevant dysfunction. Identification of the proteins participating in renal sodium re-absorption and its regulation, particularly those involved in the renal pressure-natriuresis mechanism, will allow gene cloning and sequencing which in turn may lead to the identification of novel gene sequence variation participating in hypertension.

Synergistic effect of alpha-adducin and ACE genes causes blood pressure changes with body sodium and volume expansion

BACKGROUND

The genetic dissection of a polygenic, multifactorial, quantitative disease such as arterial hypertension is hampered by a large environmental variance and by genetic heterogeneity.

METHODS

To reduce the environmental variance, we measured the pressor response to a saline load (PRSL) and the basal plasma renin activity (PRA) under very controlled conditions in 145 essential hypertensive patients, as they may have the most direct clinical expression of the putative genetic alteration in renal Na handling and blood pressure (BP) regulation caused by the alpha-adducin and angiotensin-converting enzyme (ACE) polymorphism.

RESULTS

PRSL was smaller in patients homozygous for the wild-type (Gly460) variant of alpha-adducin compared with that of patients bearing at least one copy of the 460Trp variant (2.5 +/- 0.6 vs. 7.0 +/- 0.9 mm Hg, P = 0.0001), whereas the ACE genotype was not associated with differences in PRSL. Both alpha-adducin and ACE affect PRA, with lower values correlated with the number of 460Trp or D alleles (P = 0.019 and 0.017, respectively). Most important, alpha-adducin and ACE interact epistatically in determining the PRSL, doubling the variance explained when epistasis is taken into account (variance from 7.7 to 15.5%).

CONCLUSION

These findings support the involvement of ACE and alpha-adducin in PRSL and PRA control, which are of paramount importance in setting the BP level and its response to therapy.

The role of alpha-adducin polymorphism in blood pressure and sodium handling regulation may not be excluded by a negative association study

The basic requirement for declaring an association study positive is that the "hypertension-favoring" allele is more frequent in hypertensive cases than in normotensive controls. However, both positive and negative associations with hypertension have been found for the same polymorphism when studied in different populations. In the present study, we addressed the question of the possible cause(s) of this discrepancy among populations by using the alpha-adducin polymorphism as a paradigm. Four hundred ninety hypertensives and 176 normotensives enrolled in Sassari, Italy, and 468 hypertensives and 181 normotensives enrolled in Milano, Italy, were genotyped for the alpha-adducin Gly460Trp polymorphism. The blood pressure response to 2 months of hydrochlorothiazide therapy could be evaluated in 143 (85 in Sassari and 58 in Milano) hypertensives with and without the 460Trp alpha-adducin allele. The alpha-adducin 460Trp allele was not significantly more frequent in hypertensives in the Sassari population but was more frequent in hypertensives than in normotensives in Milano (P=0.019). Basal plasma renin activity was lower and blood pressure fall after diuretic therapy more pronounced (P<0.01) in hypertensives carrying at least one 460Trp allele than in Gly460Gly homozygotes, irrespective of their membership in the Sassari or Milano cohort. The effect of alpha-adducin genotype in predicting basal plasma renin activity and blood pressure decrease with diuretic treatment is similar in Sassari and Milano, despite the lack of association of the alpha-adducin genotype with hypertension in Sassari.

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.

Adducin polymorphism affects renal proximal tubule reabsorption in hypertension

Abnormalities in renal sodium reabsorption may be involved in the development and maintenance of experimental and clinical hypertension. Adducin polymorphism is thought to regulate ion transport in the renal tubule. It has recently been shown that there is a significant linkage of alpha-adducin locus to essential hypertension and that the 460Trp allele is associated with hypertension. Patients with this allele display larger blood pressure changes with body sodium variation. The aim of this study was to test whether alpha-adducin polymorphism is involved in abnormalities of renal function. Because proximal tubular reabsorption has been shown to be tightly coupled to renal perfusion pressure, this segmental tubular function was investigated in 54 (29 Gly/Gly and 25 Gly/Trp) untreated hypertensive patients in basal conditions with the use of endogenous lithium concentration and uric acid. Fractional excretions of lithium and uric acid were significantly decreased in the Gly/Trp hypertensive patients compared with the Gly/Gly hypertensives. The contribution of alpha-adducin to fractional excretion of lithium was investigated by multiple regression analysis. Adducin genotype was significantly (R2=0.11, F=6.5; P<0.01) and directly related to fraction excretion of lithium; gender, age, urinary Na+, urinary uric acid, mean blood pressure, and plasma renin activity were not related. In conclusion, the adducin gene can be considered to be a 'renal hypertensive gene' that modulates the capacity of tubular epithelial cells to transport Na+ and hence contributes to the level of blood pressure.

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.