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

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.

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.

Associations of epithelial sodium channel genes with blood pressure: the GenSalt study

In order to investigate associations of SCNN1A, SCNN1G and SCNN1B genes with blood pressure (BP) in Han Chinese population, we included 2 880 participants did not use antihypertensive medication in the month prior to the baseline survey in the current analysis. Forty-four tag-SNPs in epithelial sodium channel (ENaC) genes were selected and genotyped and nine BP measurements were obtained during 3-day examination. In single-marker analyses, we identified significant associations of SCNN1A marker rs13306613 with diastolic BP (DBP) and SCNN1B marker rs12447134 with systolic BP (SBP) under codominant model after Bonferroni correction (P= 2.82×10⁻⁵ and 4.63×10⁻⁴, respectively). In addition, 5 SNPs in SCNN1G and 4 SNPs in SCNN1B achieved nominal significance for SBP, DBP or mean arterial pressure (MAP) under the additive model. For example, the minor C allele of rs5735 in SCNN1G gene was associated with decreased SBP, DBP and MAP (P=0.016, 5.41×10⁻³, and 4.36×10⁻³, respectively). Gene-based results showed significant associations of SCNN1G and SCNN1Bwith BP levels. This study suggested that ENaC genes play important roles in BP regulation in the Han Chinese population. Future studies are warranted to replicate these findings and functional studies are needed to identify true causal variants in ENaC genes.

Renin gene polymorphisms in bangladeshi hypertensive population

Objective: Linkages of renin gene polymorphisms with hypertension have been implicated in several populations with contrasting results. Present study aims to assess the pattern of renin gene polymorphisms in Bangladeshi hypertensive individuals.

Methodology: Introns 1, 9 of renin gene and 4063 bases upstream of promoter sequence of renin gene were amplified from the genomic DNA of the total 124 (hypertensive and normotensive) subjects using respective primers. Polymerase chain reaction-based restriction fragment length polymorphisms were performed using BglI, MboI and TaqI restriction enzymes.

Results: Homozygosity was common in renin gene regarding BglI (bb=48.4%, Bb=37.9%, BB=13.7%, χ² =1.91, P>0.05), TaqI (TT=81.5%, Tt=14.5%, tt=4.0%, χ² =7.50, P<0.01) and MboI (mm=63.7%, Mm=32.3%, MM=4.0%, χ²=0.00, P>0.05) polymorphisms among total study population. For BglI and TaqI genotype distribution, hypertensive subjects (BglI: χ² =6.66, P<0.05; TaqI: χ² = 10.28, P<0.005) significantly deviate from Hardy-Weinberg Equilibrium law compared to normotensive subjects (BglI: χ²=0.51, P>0.05; TaqI: χ²=0.20, P>0.05). On the other hand, with respect to MboI polymorphisms of renin gene, only normotensive subjects deviate from the law (patients: χ²=1.28, P>0.05; vs controls: χ²=6.81, P<0.01). In the context of allelic frequency, common T allele was clearly prevalent (T frequency=0.86, t frequency = 0.14) for TaqI, but rare alleles b and m were more frequent for both BglI (b frequency=0.69, B frequency=0.31) and MboI (m frequency=0.80 M frequency=0.20) polymorphisms, respectively.

Conclusion: Thus, we report that Bangladeshi hypertensive subjects did not show any distinct pattern of renin gene polymorphisms compared to their healthy control subjects with regard to their genotypic and allelic frequencies.

Abnormal increase in urinary aquaporin-2 excretion in response to hypertonic saline in essential hypertension

Background

Dysregulation of the expression/shuttling of the aquaporin-2 water channel (AQP2) and the epithelial sodium channel (ENaC) in renal collecting duct principal cells has been found in animal models of hypertension. We tested whether a similar dysregulation exists in essential hypertension.

Methods

We measured urinary excretion of AQP2 and ENaC β-subunit corrected for creatinine (u-AQP2_CR, u-ENaC_β-CR), prostaglandin E2 (u-PGE₂) and cyclic AMP (u-cAMP), fractional sodium excretion (FE_Na), free water clearance (C_H2O), as well as plasma concentrations of vasopressin (AVP), renin (PRC), angiotensin II (Ang II), aldosterone (Aldo), and atrial and brain natriuretic peptide (ANP, BNP) in 21 patients with essential hypertension and 20 normotensive controls during 24-h urine collection (baseline), and after hypertonic saline infusion on a 4-day high sodium (HS) diet (300 mmol sodium/day) and a 4-day low sodium (LS) diet (30 mmol sodium/day).

Results

At baseline, no differences in u-AQP2_CR or u-ENaC_β-CR were measured between patients and controls. U-AQP2_CR increased significantly more after saline in patients than controls, whereas u-ENaC_β-CR increased similarly. The saline caused exaggerated natriuretic increases in patients during HS intake. Neither baseline levels of u-PGE₂, u-cAMP, AVP, PRC, Ang II, Aldo, ANP, and BNP nor changes after saline could explain the abnormal u-AQP2_CR response.

Conclusions

No differences were found in u-AQP2_CR and u-ENaC_β-CR between patients and controls at baseline. However, in response to saline, u-AQP2_CR was abnormally increased in patients, whereas the u-ENaC_β-CR response was normal. The mechanism behind the abnormal AQP2 regulation is not clarified, but it does not seem to be AVP-dependent.

Clinicaltrial.gov identifier

NCT00345124.

Gene variants of the renin–angiotensin system and hypertension: from a trough of disillusionment to a welcome phase of enlightenment?

There is substantial evidence to suggest that BP (blood pressure) is an inherited trait. The introduction of gene technologies in the late 1980s generated a sharp phase of over-inflated prospects for polygenic traits such as hypertension. Not unexpectedly, the identification of the responsible loci in human populations has nevertheless proved to be a considerable challenge. Common variants of the RAS (renin–angiotensin system) genes, including of ACE (angiotensin-converting enzyme) and AGT (angiotensinogen) were some of the first shown to be associated with BP. Presently, ACE and AGT are the only gene variants with functional relevance, where linkage studies showing relationships with hypertension have been reproduced in some studies and where large population-based and prospective studies have demonstrated these genes to be predictors of hypertension or BP. Nevertheless, a lack of reproducibility in other linkage and association studies has generated scepticism that only a concerted effort to attempt to explain will rectify. Without these explanations, it is unlikely that this knowledge will translate into the clinical arena. In the present review, we show that many of the previous concerns in the field have been addressed, but we also argue that a considerable amount of careful thought is still required to achieve enlightenment with respect to the role of RAS genes in hypertension. We discuss whether the previously identified problems of poor study design have been completely addressed with regards to the impact of ACE and AGT genes on BP. In the context of RAS genes, we also question whether the significance of ‘incomplete penetrance’ through associated environmental, phenotypic or physiological effects has been duly accounted for; whether appropriate consideration has been given to epistatic interactions between genes; and whether future RAS gene studies should consider variation across the gene by evaluating ‘haplotypes’.

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.

The stationary distribution of allele frequencies when selection acts at unlinked loci

We consider population genetics models where selection acts at a set of unlinked loci. It is known that if the fitness of an individual is multiplicative across loci, then these loci are independent. We consider general selection models, but assume parent-independent mutation at each locus. For such a model, the joint stationary distribution of allele frequencies is proportional to the stationary distribution under neutrality multiplied by a known function of the mean fitness of the population. We further show how knowledge of this stationary distribution enables direct simulation of the genealogy of a sample at a single-locus. For a specific selection model appropriate for complex disease genes, we use simulation to determine what features of the genealogy differ between our general selection model and a multiplicative model.

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.

Strong Association of a Renin Intronic Dimorphism with Essential Hypertension

The objectives of this project were two-fold: to identify the genetic mutation that has been detected as an MboI dimorphism in intron 9 of the human renin (REN) gene and to confirm a previously reported, putative association between the REN MboI dimorphism and clinical diagnosis of essential hypertension (EHT) in a population of Gulf Arabs from the United Arab Emirates. Sequencing of the MboI dimorphic site was carried out on DNA of randomly chosen cases and controls. A retrospective case-control study was carried out in 689 unrelated subjects (326 first-time, clinically diagnosed hypertensives and 363 age- and gender-matched normotensive subjects), selected from the resident population of the Abu Dhabi Emirate. A polymerase chain reaction/MboI-RFLP based method was employed to compare genotype and allele distributions. Nucleotide sequences at the MboI site of the cut and uncut alleles were determined to be GATC and GGTC, respectively. This A>G mutation is located 10,631 base pairs (bp) 3' to the start of the REN gene, and 79 bp 3' to the end of exon 9. The genotype distributions of the REN 10631A>G dimorphism were found to be significantly different between hypertensive and normotensive subjects (x2= 42.29, df=2, p<0.001). Frequencies of A alleles were 0.54 in EHT vs. 0.37 in normotensive subjects, which is even more demarcated than what was found previously. The frequency of AA genotypes was higher in the hypertensive group than in the normotensive group (34.7% vs. 14.0%). The quantification of the association of A alleles with increased risk of EHT was assessed with corresponding odds ratios (OR), which gave the following values: OR of GG vs. AG genotypes, 1.3 (95% confidence interval [CI]: 0.90-1.88); OR of GG vs. AA, 3.75 (95% CI: 2.41-5.86). In conclusion, REN 10631A alleles are significantly associated with EHT in the Emirati population. This has now been found in two different and therefore independent sample populations from the Abu Dhabi Emirate. Moreover, this genetic effect seems to be acting in a recessive fashion. Hence, either the REN gene itself, or another gene that is in linkage disequilibrium with REN 10631A>G, is implicated in the pathogenesis of EHT in Emirati.

Multilocus analysis of hypertension: a hierarchical approach

While hypertension is a complex disease with a well-documented genetic component, genetic studies often fail to replicate findings. One possibility for such inconsistency is that the underlying genetics of hypertension is not based on single genes of major effect, but on interactions among genes. To test this hypothesis, we studied both single locus and multilocus effects, using a case-control design of subjects from Ghana. Thirteen polymorphisms in eight candidate genes were studied. Each candidate gene has been shown to play a physiological role in blood pressure regulation and affects one of four pathways that modulate blood pressure: vasoconstriction (angiotensinogen, angiotensin converting enzyme - ACE, angiotensin II receptor), nitric oxide (NO) dependent and NO independent vasodilation pathways and sodium balance (G protein-coupled receptor kinase, GRK4). We evaluated single site allelic and genotypic associations, multilocus genotype equilibrium and multilocus genotype associations, using multifactor dimensionality reduction (MDR). For MDR, we performed systematic reanalysis of the data to address the role of various physiological pathways. We found no significant single site associations, but the hypertensive class deviated significantly from genotype equilibrium in more than 25% of all multilocus comparisons (2,162 of 8,178), whereas the normotensive class rarely did (11 of 8,178). The MDR analysis identified a two-locus model including ACE and GRK4 that successfully predicted blood pressure phenotype 70.5% of the time. Thus, our data indicate epistatic interactions play a major role in hypertension susceptibility. Our data also support a model where multiple pathways need to be affected in order to predispose to hypertension.

Human genome research in China

Significant progress in human genome research has been made in China since 1994. This review aims to give a brief and incomplete introduction to the major research institutions and their achievements in human genome sequencing and functional genomics in medicine, with emphasis on the "1% Sequencing Project", the generation of single nucleotide polymorphism and haplotype maps of the human genome, disease gene identification, and the molecular characterization of leukemia and other diseases. Chinese efforts towards the sequencing of pathogenic microbial genomes and of the rice (Oryza sativa ssp. Indica) genome are also described.

The G???217A variant of the angiotensinogen gene affects basal transcription and is associated with hypertension in a Taiwanese population

OBJECTIVE

Polymorphisms of the angiotensinogen (AGT) gene, especially in the promoter region, are in linkage concordance and are associated with hypertension. In this study, we examined the role of AGT promoter polymorphisms, including G-217A, A-6G and M235T variants, and their promoter function in essential hypertension in Taiwanese populations.

DESIGN

An association study was conducted to assess the genotype distribution between hypertensive patients and normotensive subjects. We also used a transient transfection assay to examine basal transcriptional activity of G-217A and A-6G variants in a mammalian cell system.

METHODS

Hypertensive subjects (390) and normotensive controls (388) of Taiwanese ethnicity were genotyped for the AGT G-217A, A-6G and M235T variants. Promoter activity was studied by cloning the promoter region (-614 to +41 bp) of AGT into the pSEAP2-Basic reporter vector and performing a transient transfection assay in HuH7 and HepG2 cells.

RESULTS

The G-217A variant of the AGT gene was significantly associated with hypertension (P = 0.0047), but the A-6G and M235T polymorphisms were not (P = 0.17 and P = 0.33, respectively). Furthermore, the recessive model of homozygous genotype (-217AA) conferred a high risk for hypertension (odds ratio 3.64) in this population. The -217A variant expressed higher transcriptional activity than -217G in vitro.

CONCLUSIONS

Our study showed a significant association between the -217A variant of the AGT gene and hypertension. This variant plays a functional role in basal transcription of AGT, and may confer a risk for hypertension in Taiwanese populations.

Ancestral processes for non-neutral models of complex diseases

We consider non-neutral models for unlinked loci, where the fitness of a chromosome or individual is not multiplicative across loci. Such models are suitable for many complex diseases, where there are gene-interactions. We derive a genealogical process for such models, called the complex selection graph (CSG). This coalescent-type process is related to the ancestral selection graph, and is derived from the ancestral influence graph by considering the limit as the recombination rate between loci gets large. We analyse the CSG both theoretically and via simulation. The main results are that the gene-interactions do not produce linkage disequilibrium, but do produce dependencies in allele frequencies between loci. For small selection rates, the distributions of the genealogy and the allele frequencies at a single locus are well-approximated by their distributions under a single locus model, where the fitness of each allele is the average of the true fitnesses of that allele with respect to the distribution of alleles at other loci.

Linkage analysis of 2q14-q23 and 5q32 with blood pressure quantitative traits in Chinese sib pairs

OBJECTIVES

Several genome-wide scans recently accomplished in the ethnic Chinese revealed a number of candidate loci possibly contributing to essential hypertension, and some appeared to be replicable in 2q14-q23 and 5q32. The current study aimed to examine the linkage of qualitative and blood pressure quantitative traits in essential hypertension with these genomic regions in a large sample of Chinese hypertensive families.

METHODS

We performed a genetic analysis on 148 randomly ascertained families containing 328 affected sib pairs, grouped into two geographically distinct subsets. Five highly informative microsatellite markers (D2S151, D2S142, D5S2090, D5S413 and D5S2013) were genotyped, and linkage analyses were performed with different genetic models.

RESULTS

We did not observe consistent evidence for excess allele sharing identity by descent in either of the qualitative or the quantitative test. However, higher LOD scores were found at D5S2013 in North Group subset with Haseman-Elston and maximum likelihood (ML) variance (no dominance variance, NDV) algorithms. With the ML (NDV) algorithm, the LOD was 1.410 for diastolic blood pressure at this locus, although this was not statistically significant.

CONCLUSIONS

These findings provide no evidence to support a significant linkage of 2q14-q23 or 5q32 with essential hypertension or blood pressure quantitative traits in the ethnic Chinese, and indicate the aetiologic diversity and complexity of hypertension. Previous reports implied 2q14-q23 or beta 2- adrenergic receptor gene potentially linked to essential hypertension in the ethnic Chinese. To replicate these results and perform quantitative linkage analysis, we genotyped members of 148 hypertensive families with five highly informative microsatellite markers. We observed no evidence of excess allele sharing identity by descent in sib pairs, revealing a lack of linkage between 2q14-q23 or 5q32 (chromosome region harboring the gene encoding beta 2 adrenergic receptor) and hypertension in our study sample.

Linkage analysis of five candidate genes and essential hypertension in 106 Chinese nuclear families

Five candidate genes including the lipoprotein lipase, leptin, leptin receptor, alpha-adducin and beta3 adrenergic receptor were selected to examine their possible contribution to essential hypertension (EH) in a Chinese population. On each side of the candidate gene loci, one to two highly polymorphic microsatellite markers were genotyped in 474 subjects recruited from 106 hypertension nuclear families in Shanghai. Both parametric and nonparametric linkage analyses were carried out using GENEHUNTER (version 2.0) after genotyping. Extended transmission disequilibrium testing (ETDT) was also conducted to detect preferential transmission of alleles to affected offspring. We failed to find the linkage between all these loci and EH by either parametric or nonparametric analysis, nor did we detect any significant transmission disequilibrium by ETDT. Our findings provide no support for a significant contribution of these five genes to the pathogenesis of EH among Shanghai people.

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.

A1166C polymorphism of the angiotensin II type 1 receptor gene and essential hypertension in Han, Tibetan and Yi populations

Our aim was to clarify whether substitution of cytosine for adenine at position 1166 (A1166C) polymorphism of the angiotensin II type 1 receptor (AT1R) gene is associated with susceptibility to essential hypertension in Han, Tibetan and Yi populations in China. This study involved 302 normotensive and 446 hypertensive subjects. The polymorphism was detected by polymelase chain reaction of genomic DNA and restriction fragment length polymorphism (PCR-RFLP) in genomic DNA. The data were analyzed by analysis of covariance (ANCOVA), X2 test, and multiple logistic regression. In normotensive controls, the A1166 allele frequencies were 0.979, 0.939 and 0.965 in Han, Tibetan and Yi participants, respectively. There was no significant intergroup variation in frequency of the allele in normotensives (X2=4.166, p=0.125). The frequency of the A1166 allele was significantly higher in Tibetan male hypertensives than that in normotensives (X2=11.46, p=0.001). There was no significant difference in A1166C genotype distribution and allele frequency between normotensives and hypertensives either in the Han (p=0.465) or Yi (p=0.357) populations. Body mass index in the Han and Yi populations (p=0.0001), age in the Tibetan and Yi populations (p=0.0001), and AA genotype in the Tibetan male population (p=0.0034) all were independent risk factors for hypertension. Diastolic blood pressure levels were significantly higher in Tibetan male subjects with the AA genotype than in those with the AC+CC genotype (p=0.0040). We concluded that the A1166 allele is very common in Han, Tibetan and Yi populations, approximately 1.35-fold more common than in Caucasians. The A1166 allele of the AT1R gene may be a predisposing factor for essential hypertension in Tibetan males. A1166C polymorphism of the AT1R gene is probably not involved in the pathogenesis of essential hypertension in Han or Yi populations.

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.

Power and robustness of a score test for linkage analysis of quantitative traits using identity by descent data on sib pairs

Identification of genes involved in complex traits by traditional (lod score) linkage analysis is difficult due to many complicating factors. An unfortunate drawback of non-parametric procedures in general, though, is their low power to detect genetic effects. Recently, Dudoit and Speed [2000] proposed using a (likelihood-based) score test for detecting linkage with IBD data on sib pairs. This method uses the likelihood for theta, the recombination fraction between a trait locus and a marker locus, conditional on the phenotypes of the two sibs to test the null hypothesis of no linkage (theta = (1/2)). Although a genetic model must be specified, the approach offers several advantages. This paper presents results of simulation studies characterizing the power and robustness properties of this score test for linkage, and compares the power of the test to the Haseman-Elston and modified Haseman-Elston tests. The score test is seen to have impressively high power across a broad range of true and assumed models, particularly under multiple ascertainment. Assuming an additive model with a moderate allele frequency, in the range of p = 0.2 to 0.5, along with heritability H = 0.3 and a moderate residual correlation rho = 0.2 resulted in a very good overall performance across a wide range of trait-generating models. Generally, our results indicate that this score test for linkage offers a high degree of protection against wrong assumptions due to its strong robustness when used with the recommended additive model.

The genetics of essential hypertension

Essential hypertension is an escalating problem for industrialized populations. It is currently seen as a 'complex' genetic trait caused by multiple susceptibility genes the effects of which are modulated by gene-environment and gene-gene interactions. Nevertheless, the success to date in identifying these susceptibility genes has been very limited. A number of candidates has been proposed, but demonstrating consistently the linkage or association with hypertension has been problematic. The data for angiotensinogen is undoubtedly the most extensive and meta-analysis has confirmed a significant association overall, although the risk contributed by this gene appears to be modest (odds ratio of 1.2). Identifying further genes - probably conferring even smaller attributable risks - represents a major challenge for future developments in this area. This contrasts markedly with the success that has been achieved in the past 5 years in solving the molecular genetics of a number of rare familial hypertension syndromes. The true incidences of some of these disorders may be higher than first appreciated, but it is still unclear if the genes for these syndromes also play a part in essential hypertension. A more complete understanding of the genetic basis of essential hypertension should be possible in the coming years using new strategies that take advantage of the information provided by the human genome project. This knowledge will irrevocably change the way we approach this disease in terms of its diagnosis, risk assessment for end-points such as stroke and heart disease, and the customised treatment that might be offered in the future.

Renal tubular effects of endothelin-B receptor signaling: its role in cardiovascular homeostasis and extracellular volume regulation

The role of the endothelin-B receptor in vascular homeostasis is controversial because the receptor has both pressor and depressor effects in vivo. One potential depressor mechanism of endothelin-B activation is through the promotion of natriuresis and diuresis in the renal tubule. Recent studies demonstrate that rodents genetically deficient for the endothelin-B exhibit sodium-dependent hypertension due to an absence of tonic inhibition of the epithelial sodium channel in the distal nephron. These studies suggest that the predominant role of endothelin-B receptors in the basal physiologic state may be to regulate renal sodium excretion relative to the level of oral salt intake.

Molecular genetics of human hypertension

The year 1999 saw considerable activity in the area of hypertension-related molecular genetics. Several new monogenic hypertensive disorders, as well as a monogenic form of hypotension, were elucidated. Molecular genetics has made significant inroads in explaining basic mechanisms of magnesium homeostasis. Linkage strategies have been applied in family studies, sib-pair analyses, and twin studies. More stringent criteria for association studies have been formulated. The 11 beta-hydroxysteroid dehydrogenase gene, the prostacyclin synthase gene, genes coding for variants in G proteins, and adrenergic receptor genes have received particular attention. On the horizon are better phenotyped patient and subject collectives, expanded genotyping with the availability of a 300,000 genome-wide single-nucleotide polymorphism map, multigenic studies in the form of metabolic control analyses, and new bioinformatic strategies including neural networks.