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

Single nucleotide polymorphism rs4961 in the adducin 1 gene is not associated with gastric cancer or preneoplastic cancer lesions

Gastric cancer (GC) is the fourth most deadly cancer globally. The adducin 1 (ADD1) protein is involved in oncogenic signal transduction pathways in several types of cancer, and the rs4961 variant (c.1378 G>T, p.Gly460Trp) of the ADD1 gene is associated with salt-sensitive hypertension, renal cell cancer and breast cancer susceptibility; however, it has not been investigated in GC. The aim of the present study was to evaluate the association between the rs4961 variant and the development of GC and preneoplastic gastric lesions (PGLs) in a population from western Mexico. A total of 225 individuals who underwent an endoscopy were evaluated, of which 71 patients had histopathologically diagnosed GC and 53 patients had PGLs, with 101 patients used as controls. The rs4961 variant was genotyped by using PCR and DNA sequencing. The frequency of the mutated homozygous genotype (TT) of the rs4961 variant was <10% in the three evaluated groups, and the frequency of the minor allele (T) was <21% in the GC, PGL and control groups. Genotypic and allelic frequencies were similarly distributed in all of the studied groups (P>0.05). In summary, in the study population, the rs4961 variant was not associated with GC risk; however, its role in other populations and in other types of cancer is worthy of future research.

ADD1 Single Nucleotide Polymorphisms Are Associated With Essential Hypertension Among Han and Mongolian Population in Inner Mongolia Area

Aldosterone synthase (CYP11B2) and α-adducing (ADD1) are candidate genes that play key roles during essential hypertension (EH) incidence. However, the association between their genetic mutations and the risk of EH is unclear. The present study investigated specific single nucleotide polymorphisms (SNPs) from CYP11B2 and ADD1, and their potential role as risk factors for EH based on 423 Mongolian and 410 Han people in Inner Mongolia province. In the allelic model, people with ADD1 rs2239728-A presented a 0.74-fold risk than rs2239728-C, whereas the ADD1 rs4961-T was associated with a 1.37-fold higher risk than allele G in the Han population. The genetic model reported that the rs2239728-A carrier (AA + AC) was 0.59-fold lower than the CC carrier, whereas the rs4961-G carrier (GG + GT) was 0.59-fold lower than the TT carrier in the dominant model. After gender adjustment, people with rs2239728-A was a 0.63-fold risk than –C in EH, but the rs4961-T carrier was associated with a 1.63-times higher risk than –G in females. Haplotype analysis showed that GCCT was associated with essential hypertension in the Han population, and it was a risk factor for EH. Our identification reported novel SNPs of ADD1 with protective significance for EH among females in the Chinese Han population, together with its haplotype GCCT as a risk factor for EH.

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 on Adducin from Functional to Pathological Mechanisms: Future Direction in Cancer

Adducin (ADD) is a family of membrane skeleton proteins including ADD1, ADD2, and ADD3 that are encoded by distinct genes on different chromosomes. Adducin is primarily responsible for the assembly of spectrin-actin network that provides physical support to the plasma membrane and mediates signal transduction in various cellular physiological processes upon regulation by protein kinase C-dependent and calcium/calmodulin-dependent pathways. Abnormal phosphorylation, genetic variations, and alternative splicing of adducin may contribute to alterations in cellular functions involved in pathogenic processes. These alterations are associated with a wide range of diseases including cancer. This paper begins with a discussion on how adducin partakes in the structural formation of membrane skeleton, its regulation, and related functional characteristics, followed by a review on the pathogenesis of hypertension, biliary atresia, and cancer with respect to increased disease susceptibility mediated by adducin polymorphism and/or dysregulation. Given the functional diversity of adducin in different cellular compartments, we aim to provide a knowledge base whereby its pathophysiological roles can be better understood. More importantly, we aim to provide novel insights that may be of significance in turning the adducin model to clinical application.

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.

Synergistic Association of Genetic Variants with Environmental Risk Factors in Susceptibility to Essential Hypertension

AIMS

Essential hypertension (EH) is a disease in which both environment and genes have an important role. This study was designed to identify the interaction model between genetic variants and environmental risk factors that most highly potentiates EH development.

METHODS

We performed a case-control study with 1641 participants (mean age 50.6 ± 8.1 years), specifically 848 patients with EH and 793 controls, adjusted for gender and age. Traditional risk factors, biochemical and genetic parameters, including the genotypic discrimination of 14 genetic variants previously associated with EH, were investigated. Multifactorial dimensionality reduction (MDR) software was used to analyze gene-environment interactions. Validation was performed using logistic regression analysis with environmental risk factors, significant genetic variants, and the best MDR model.

RESULTS

The best model indicates that the interactions among the ADD1 rs4961 640T allele, diabetes, and obesity (body mass index ≥30) increase approximately four-fold the risk of EH (odds ratio = 3.725; 95% confidence interval: 2.945-4.711; p < 0.0001).

CONCLUSION

This work showed that the interaction between the ADD1 rs4961 variant, obesity, and the presence of diabetes increased the susceptibility to EH four-fold. In these circumstances, lifestyle adjustment and diabetes control should be intensified in patients who carry the ADD1 variant.

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.

Variation in genes that regulate blood pressure are associated with glomerular filtration rate in Chinese

Chronic kidney disease (CKD) can be a consequence of diabetes, hypertension, immunologic disorders, and other exposures, as well as genetic factors that are still largely unknown. Glomerular filtration rate (GFR), which is widely used to measure kidney function, has a heritability ranging from 25% to 75%, but only 1.5% of this heritability is explained by genetic loci that have been identified to date. In this study we tested for associations between GFR and 234 SNPs in 26 genes from pathways of blood pressure regulation in 3,025 rural Chinese participants of the "Genetic Epidemiology Network of Salt Sensitivity" (GenSalt) study. We estimated GFR (eGFR) using baseline serum creatinine measurements obtained prior to dietary intervention. We identified significant associations between eGFR and 12 SNPs in 6 genes (ACE, ADD1, AGT, GRK4, HSD11B1, and SCNN1G). The cumulative effect of the protective alleles was an increase in mean eGFR of 4 mL/min per 1.73 m2, while the cumulative effect of the risk alleles was a decrease in mean eGFR of 3 mL/min per 1.73 m2. In addition, we identified a significant interaction between SNPs in CYP11B1 and ADRB2. We have identified common variants in genes from pathways that regulate blood pressure and influence kidney function as measured by eGFR, providing new insights into the genetic determinants of kidney function. Complex genetic effects on kidney function likely involve interactions among genes as we observed for CYP11B1 and ADRB2.

α-Adducin Gly460Trp gene mutation and essential hypertension in a Chinese population: a meta-analysis including 10,960 subjects

Background

The α-adducin Gly460Trp (G460W) gene polymorphism may be associated with susceptibility to essential hypertension (EH), but this relationship remains controversial. In an attempt to resolve this issue, we conducted a meta-analysis.

Methods

Twenty-three separated studies involving 5939 EH patients and 5021 controls were retrieved and analyzed. Four ethnicities were included: Han, Kazakh, Mongolian, and She. Eighteen studies with 5087 EH patients and 4183 controls were included in the Han subgroup. Three studies with 636 EH patients and 462 controls were included in the Kazakh subgroup. The Mongolian subgroup was represented by only one study with 100 EH patients and 50 controls; similarly, only one study with 116 EH patients and 326 controls was available for the She subgroup. The pooled and ethnic group odds ratios (ORs) along with the corresponding 95% confidence intervals (95% CI) were assessed using a random effects model.

Results

There was a significant association between the α-adducin G460W gene polymorphism and EH in the pooled Chinese population under both an allelic genetic model (OR: 1.12, 95% CI: 1.04–1.20, P = 0.002) and a recessive genetic model (OR: 1.40, 95% CI: 1.16–1.70, P = 0.0005). In contrast, no significant association between the α-adducin G460W gene polymorphism and EH was observed in the dominant genetic model (OR: 0.88, 95% CI: 0.72–1.09, P = 0.24). In stratified analysis by ethnicity, significantly increased risk was detected in the Han subgroup under an allelic genetic model (OR: 1.13, 95% CI: 1.04–1.23, P = 0.003) and a recessive genetic model (OR: 1.43, 95% CI: 1.17–1.75, P = 0.0006).

Conclusions

In a Chinese population of mixed ethnicity, the α-adducin G460W gene polymorphism was linked to EH susceptibility, most strongly in Han Chinese.

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.

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 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.

Review: Association between angiotensin converting enzyme G2350A polymorphism and hypertension risk: a meta-analysis

Background and objective: An exonic polymorphism G2350A (rs4343) in angiotensin converting enzyme (protein: ACE; gene: ACE) was shown to exert the most significant influence on plasma ACE levels. We therefore performed a meta-analysis to investigate association of ACE G2350A polymorphism with hypertension.

Methods: Published case-control studies in English were identified. A total of four studies with 1699 cases and 1274 controls were identified. A random-effects model was performed irrespective of the between-study heterogeneity. Study quality was assessed in duplicate.

Results: Compared with 2350G, the ACE 2350A allele conferred a protective effect on hypertension (odds ratio (OR) = 0.81; 95% confidence interval (CI), 0.56—1.18; p = .28). Similarly, comparisons of 2350AA and 2350GA with 2350GG generated a nonsignificant reduced risk, respectively. Under the dominant model, the ACE 2350A allele conferred a reduced hypertension risk and such associations were divergent between Han Chinese and Muslims from the Arab Gulf and Pakistan. Under the recessive model, this protective effect was totally reversed (OR = 1.01; 95% CI, 0.77—1.33; p = .94). Subgroup analyses indicated a significant protective effect of ACE 2350A compared with 2350G among Muslims from the Arab Gulf and Pakistan (OR = 0.55; 95% CI, 0.42—0.71; p < .00001). No publication biases were observed.

Conclusions: Our results demonstrate that the ACE 2350A allele is associated with a significantly reduced hypertension risk among Muslims from the Arab Gulf and Pakistan, yet an elevated risk among Han Chinese.

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

BACKGROUND AND OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

α-Adducin Gly 460 Trp Variant Increases the Risk of Stroke in Hypertensive Dutch Women

The Gly 460 Trp variant of the α-adducin gene has been associated with renal sodium retention and salt-sensitive hypertension. Independent of blood pressure, salt sensitivity has been related to cerebrovascular events. We studied the risk of stroke, coronary heart disease (CHD), and myocardial infarction (MI) associated with the α-adducin variant and examined the extent to which this risk is modified by the presence of hypertension. We performed a case-cohort study in a prospective cohort of 15 236 initially healthy Dutch women. We applied a Cox proportional hazards model with an estimation procedure adapted for case-cohort designs to study the relation of the polymorphism and CHD (n=210), MI (n=71), any stroke (n=74), and ischemic stroke (n=49). Subjects with the Gly 460 Trp variant had a 2.8 times higher risk of stroke (95% confidence intervals [CI] 1.3 to 5.8) under the dominant genetic model, which did not attenuate after adjustment. The same pattern was found under per-allele comparison. Risk of ischemic stroke in the variant allele carriers was 3.9 times higher than in subjects with the common genotype (95% CI 1.7 to 8.6) using dominant inheritance model. The same patterns were found under per-allele comparison. CHD and MI were not related to the variant. The risk of ischemic stroke was more pronounced among women with systolic hypertension (10.9; 95% CI 3.6 to 31.5). The findings in this prospective study in a population based cohort of Dutch women strongly suggest that presence of the α-adducin Gly 460 Trp polymorphism increases the risk of stroke. This risk is particularly elevated in the presence of systolic hypertension.

Association of alpha-adducin Gly460Trp polymorphism with coronary artery disease in a Korean population

OBJECTIVE

Coronary artery disease is caused by multiple genetic and environmental factors. The disease is also closely associated with cardiovascular conditions such as hypertension. In order to investigate any possible role of hypertension candidate genes in the disease development and progression, we examined the association of the polymorphisms of 31 hypertension candidate genes with coronary artery disease.

METHODS

Genetic polymorphisms of 31 hypertension candidate genes were initially screened by resequencing DNA samples from 24 unrelated individuals in a Korean population. Association analysis was performed using 1284 unrelated Korean men, including 749 coronary artery disease subjects and 535 normal healthy controls.

RESULTS

We identified a total of 409 single nucleotide polymorphisms including 40 nonsynonymous single nucleotide polymorphisms, 32 insertions/deletions and four microsatellites. Among 40 nonsynonymous single nucleotide polymorphisms, 29 were examined for an association with coronary artery disease. A significant association with coronary artery disease was observed in a polymorphism of the ADD1 gene (Gly460Trp; +29017G/T) (odds ratio 0.71-0.81; P = 0.01-0.04). The same polymorphism was also associated with the number of arteries with significant coronary artery stenosis in the coronary artery disease patients (P = 0.01) as well as the increase in systolic blood pressure (P = 0.02).

CONCLUSIONS

The ADD1 Gly460Trp polymorphism is significantly associated with an increased risk of coronary artery disease as well as blood pressure, indicating that ADD1 plays a role in the pathogenesis of coronary artery disease as well as hypertension.

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.

Genetics of arterial hypertension and hypotension

Human hypertension affects affects more than 20% of the adult population in industrialized countries, and it is implicated in millions of deaths worldwide each year from stroke, heart failure and ischemic heart disease. Available evidence suggests a major genetic impact on blood pressure regulation. Studies in monogenic hypertension revealed that renal salt and volume regulation systems are predominantly involved in the genesis of these disorders. Mutations here affect the synthesis of mineralocorticoids, the function of the mineralocorticoid receptor, epithelial sodium channels and their regulation by a new class of kinases, termed WNK kinases. It has been learned from monogenic hypotension that almost all ion transporters involved in the renal uptake of Na(+) have a major impact on blood pressure regulation. For essential hypertension as a complex disease, many candidate genes have been analysed. These include components of the renin-angiotensin-aldosterone system, adducin, beta-adrenoceptors, G protein subunits, regulators of G protein signalling (RGS) proteins, Rho kinases and G protein receptor kinases. At present, the individual impact of common polymorphisms in these genes on the observed blood pressure variation, on risk for stroke and as predictors of antihypertensive responses remains small and clinically irrelevant. Nevertheless, these studies have greatly augmented our knowledge on the regulation of renal functions, cellular signal transduction and the integration of both. Together, this provides the basis for the identification of novel drug targets and, hopefully, innovative antihypertensive drugs.

Pharmacogenomics and Pharmacogenetics of Hypertension: Update and Perspectives—The Adducin Paradigm: Figure 1

There is a growing literature on the potential prospective use of genome information to enhance success in finding new medicines. An example of a prospective efficacy of pharmacogenetic and pharmacogenomics is the detection and impact of adducin polymorphism on hypertension. Adducin is a heterodimeric cytoskeleton protein, the three subunits of which are encoded by genes (ADD1, ADD2, and ADD3) that map to three different chromosomes. A long series of parallel studies in the Milan hypertensive rat strain model of hypertension and humans indicated that an altered adducin function might cause hypertension through an enhanced constitutive tubular sodium reabsorption. In particular, six linkage studies, 18 of 20 association studies, and four of five follow-up studies that measured organ damage in hypertensive patients support the clinical impact of adducing polymorphism. As many modulatory genes and environment affect the adducin activity, the context must be taken into account to measure the clinical effect size of adducins. Pharmacogenomics is giving an important contribution to this end. In particular, the selective advantages of diuretics in preventing myocardial infarction and stroke over other antihypertensive therapies that produce a similar BP reduction in carriers of the mutated adducin may support new strategies that aim to optimize the use of antihypertensive agents for the prevention of hypertension-associated organ damage.

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.

Adducin Polymorphism

Adducin is a heterodymeric cytoskeleton protein, the 3 subunits of which are encoded by genes ( ADD1 , ADD2 , ADD3 ) mapping to 3 different chromosomes. A long series of parallel studies in the Milan hypertensive rat strain model of hypertension and humans indicated that an altered adducin function may cause hypertension through an enhanced constitutive tubular sodium reabsorption. Six human linkage studies showed positive results when a DNA marker mapping to 30 kb from the ADD1 locus or single-nucleotide polymorphisms (SNPs) of 1 of the 3 adducin genes were considered either alone or in combination with each other or angiotensin-converting enzyme (ACE) D allele or salt intake. When DNA markers mapping at much larger distance from the ADD1 locus were used, negative results were found by 4 studies. Positive results were also obtained in 18 of 20 association studies that, in addition to blood pressure, investigated variables reflecting body sodium or the renin-angiotensin system. Mixed results regarded case-control studies or studies in predominantly normotensive populations that did not consider the above-mentioned variables. Four of 5 studies showed a selective beneficial effect of diuretics in carriers of the mutated ADD1. Twelve of 16 studies found that ADD1 polymorphism alone or in combination with that of ACE positively associates with stroke or coronary heart disease or renal or vascular dysfunctions. In conclusion, when context is taken into account, the impact of adducin in hypertension and its related disorders is clear.

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.