Variation at the M235T locus of the angiotensinogen gene and essential hypertension: a population-based case-control study from Rochester, Minnesota

Analysis of the combined effect of rs699 and rs5051 on angiotensinogen expression and hypertension

Background

Hypertension (HTN) involves genetic variability in the renin-angiotensin system and influences antihypertensive response. We previously reported that angiotensinogen (AGT) messenger RNA (mRNA) is endogenously bound by miR-122-5p and rs699 A > G decreases reporter mRNA in the microRNA functional-assay PASSPORT-seq. The AGT promoter variant rs5051 C > T is in linkage disequilibrium (LD) with rs699 A > G and increases AGT transcription. The independent effect of these variants is understudied due to their LD therefore we aimed to test the hypothesis that increased AGT by rs5051 C > T counterbalances AGT decreased by rs699 A > G, and when these variants occur independently, it translates to HTN-related phenotypes.

Methods

We used in silico, in vitro, in vivo, and retrospective models to test this hypothesis.

Results

In silico, rs699 A > G is predicted to increase miR-122-5p binding affinity by 3%. Mir-eCLIP results show rs699 is 40-45 nucleotides from the strongest microRNA-binding site in the AGT mRNA. Unexpectedly, rs699 A > G increases AGT mRNA in an AGT-plasmid-cDNA HepG2 expression model. Genotype-Tissue Expression (GTEx) and UK Biobank analyses demonstrate liver AGT expression and HTN phenotypes are not different when rs699 A > G occurs independently from rs5051 C > T. However, GTEx and the in vitro experiments suggest rs699 A > G confers cell-type-specific effects on AGT mRNA abundance, and suggest paracrine renal renin-angiotensin-system perturbations could mediate the rs699 A > G associations with HTN.

Conclusions

We found that rs5051 C > T and rs699 A > G significantly associate with systolic blood pressure in Black participants in the UK Biobank, demonstrating a fourfold larger effect than in White participants. Further studies are warranted to determine if altered antihypertensive response in Black individuals might be due to rs5051 C > T or rs699 A > G. Studies like this will help clinicians move beyond the use of race as a surrogate for genotype.

Angiotensinogen as a Therapeutic Target for Cardiovascular and Metabolic Diseases

AGT (angiotensinogen) is the unique precursor for the generation of all the peptides of the renin-angiotensin system, but it has received relatively scant attention compared to many other renin-angiotensin system components. Focus on AGT has increased recently, particularly with the evolution of drugs to target the synthesis of the protein. AGT is a noninhibitory serpin that has several conserved domains in addition to the angiotensin II sequences at the N terminus. Increased study is needed on the structure-function relationship to resolve many unknowns regarding AGT metabolism. Constitutive whole-body genetic deletion of Agt in mice leads to multiple developmental defects creating a challenge to use these mice for mechanistic studies. This has been overcome by creating Agt-floxed mice to enable the development of cell-specific deficiencies that have provided considerable insight into a range of cardiovascular and associated diseases. This has been augmented by the recent development of pharmacological approaches targeting hepatocytes in humans to promote protracted inhibition of AGT synthesis. Genetic deletion or pharmacological inhibition of Agt has been demonstrated to be beneficial in a spectrum of diseases experimentally, including hypertension, atherosclerosis, aortic and superior mesenteric artery aneurysms, myocardial dysfunction, and hepatic steatosis. This review summarizes the findings of recent studies utilizing AGT manipulation as a therapeutic approach.

Angiotensinogen (AGT) M235T, AGT T174M and Angiotensin-1-Converting Enzyme (ACE) I/D Gene Polymorphisms in Essential Hypertension: Effects on Ramipril Efficacy

Background:

Hypertension, one of the most important risk factors for premature cardiovascular disease, is a major worldwide public health problem. Angiotensin-1-converting enzyme (ACE) and angiotensinogen (AGT) gene polymorphisms are thought to be associated with primary hypertension. In the present study, we examined the frequency of these gene polymorphisms in an adult population with and without essential hypertension. Furthermore, we evaluated the effect of ACE and AGT gene polymorphisms on ramipril treatment efficacy in the hypertensive patients.

Methods:

A total of 166 adults (83 hypertensives and 83 normotensives) were involved in the study and genotyped for AGTM235T (rs699), AGTT174M (rs4762) and ACEI/D (rs1799752) gene polymorphisms.

Results:

The genotype and allele distribution of the AGTM235T variant significantly differed between hypertensives and normotensives [odds ratio (OR) = 1.57% (T vs M allele), 95% confidence intervals (CIs): 1.01 - 2.44; p=0.045 for hypertensives]. However, none of the 3 studied Simple Nucleotide Polymorphisms were associated with the blood pressure-lowering response to ramipril.

Conclusion:

These results suggest that AGTM235T gene polymorphism is associated with essential hypertension. However, none of the AGTM235T, AGTT174M and ACEI/D gene polymorphisms influenced ramipril effectiveness.

Gender specific association of RAS gene polymorphism with essential hypertension: a case-control study

Renin-angiotensin system (RAS) polymorphisms have been studied as candidate risk factors for hypertension with inconsistent results, possibly due to heterogeneity among various genetic and environmental factors. A case-control association study was conducted to investigate a possible involvement of polymorphisms of three RAS genes: AGT M235T (rs699), ACE I/D (rs4340) and G2350A (rs4343), and AGTR1 A1166C (rs5186) in essential hypertensive patients. A total of 211 cases and 211 controls were recruited for this study. Genotyping was performed using PCR-RFLP method. The genotype and allele distribution of the M235T variant differed significantly in hypertensives and normotensives (OR-CI = 2.62 (1.24–5.76), P = 0.006; OR-CI = 0.699 (0.518–0.943), P = 0.018), respectively. When the samples were segregated based on sex, the 235TT genotype and T allele were predominant in the female patients (OR-CI = 5.68 (1.60-25.10), P = 0.002; OR-CI = 0.522 (0.330–0.826), P = 0.005) as compare to the male patients (OR-CI = 1.54 (1.24–5.76), P = 0.34; OR-CI = 0.874 (0.330–0.826), P = 0.506), respectively. For ACE DD variant, we found overrepresentation of “I”-allele (homozygous II and heterozygous ID) in unaffected males which suggest its protective role in studied population (OR-CI = 0.401 (0.224–0.718); P = 0.0009). The M235T variant of the AGT is significantly associated with female hypertensives and ACE DD variant could be a risk allele for essential hypertension in south India.

Novel variants detected in AGT gene among patients with essential hypertension

INTRODUCTION

AGT is the first gene to be linked to essential hypertension (EHT). It harbors several variants of which only few polymorphisms are found to exhibit positive and negative associations with hypertension. In the present study, the AGT gene was screened to detect already reported and novel variations contributing to the development of hypertension.

METHOD

In total, 215 hypertensives and 230 normotensives were screened for variations in all the five exons and a part of promoter of AGT gene using single strand conformation polymorphism analysis followed by sequencing of samples showing mobility shifts on polyacrylamide gels.

RESULTS

Five novel variants, namely c.-61G>A in promoter, c.-4+17C>T in intron1, c.24T>C and c.28A>T in Exon2, and c.*90 T>C in 3' untranslated region were detected in the AGT gene. c.-61G>A lies in the promoter region that plays a critical role in its expression. Variation c.-4+17C>T created a new enhancer site. c.24T>C (TCT-TCC) is a silent mutation while c.28A>T (p. M10L) has a possible damaging effect on the AGT protein. c.*90T>C, detected in the 3' untranslated region is thought to play an important role in the translation and stability of the mRNA.

CONCLUSION

Studies on the functional role of these novel variants are warranted to understand the mechanism underlying the development of EHT.

The AGT and the GNB3 polymorphisms and insulin resistance in prehypertension

OBJECTIVE

This study surveyed the frequencies of single nucleotide polymorphisms (SNPs) M235T AGT and C825T GNB3, and their association with insulin resistance, other biochemical markers and qualitative variables in subjects with high normal blood pressure and/or prehypertension in the Greek population.

DESIGN

330 men and women of Greek origin were divided into 3 groups: a) hypertensive, b) prehypertensive and c) control group. These groups were genetically tested for these polymorphisms and insulin resistance with the HOMA index.

RESULTS

No statistically significant differences were found among the polymorphisms of the compared groups. However, the ? allele carriers (CT/TT vs. CC) of the C825T polymorphism were associated with an increased BMI in all 3 groups (p=0.004). The HOMA index was higher in the hypertensive (p=0.006) and prehypertensive (p=0.016) versus the control group, and similar results were found for insulin (hypertensive vs. control p=0.012, prehypertensive vs. control p=0.001) without statistical significance between the first 2 groups (p=0.522). Additionally, there was a statistically significant difference between the control group and the hypertensive and prehypertensive groups regarding cholesterol (control vs. hypertensive p=0.001, control vs. prehypertension p=0.018) and triglycerides (control vs. hypertensive p=0.0001, control vs. prehypertension p=0.007). Differences were also noted between the control and the hypertensive group regarding the value of HDL (p=0.005) and LDL (p=0.013).

CONCLUSION

This study failed to demonstrate a correlation between specific SNPs, blood pressure and insulin resistance in the 3 groups. However, T allele carriers of the polymorphism C825T were found to have an increased BMI. Similarly, increased insulin resistance and lipidemia were more common in the hypertensive and prehypertensive populations.

Angiotensin converting enzyme I/D, angiotensinogen M235T and AT1-R A/C1166 gene polymorphisms in patients with acromegaly

Acromegaly is associated with increased morbidity and mortality related to cardiovascular disease. Hypertension is one of the most common cardiovascular risk factors in acromegalic patients. The aim of this study was to investigate association between the frequencies of angiotensin converting enzyme (ACE) I/D, angiotensinogen (AGT) M235T and the angiotensin II type 1 receptor (AT1-R) A/C1166 gene polymorphisms and some clinical parameters of acromegalic patients. Total of 33 acromegalic patients and 63 controls were enrolled to study. We determined the ACE I/D, AGT M235T and AT1-R A/C1166 gene polymorphisms. Serum insulin, glucose, triglyceride, HDL-cholesterol, LDL-cholesterol, growth hormone and Insulin-like growth factor I (IGF-I) levels of subjects were analyzed. The frequencies of ACE and M235T AGT genotype were not significantly different between control and patients. The distribution of AT1R A/C1166 genotypes was significantly different between patients and control subjects (P=0.016). None of the three ACE genotypes, DD, ID and II displayed significant difference in acromegalic patients. A significant difference in systolic blood pressure and the serum IGF-I levels among the three AGT genotype, MM, MT and TT genotypes was found in patient group. Individuals with MT genotypes had significantly higher serum IGF-I levels and systolic blood pressure than MM and TT genotype subjects, P<0.05. In addition, serum triglyceride and HDL levels differed significantly between MM and MT genotypes, P<0.05. However, systolic blood pressure of patients with CC genotypes was found to be significantly higher than AA genotypes individuals in acromegaly group, P<0.05. It can be said that the angiotensinogen MT and AT1R CC1166 genotype carriers may have more risk than other genotypes in the development of hypertension in acromegaly.

Multi-locus interactions of vascular homeostasis genes in essential hypertension: a gender-based study

BACKGROUND

Studies on genes of endothelial and vascular homeostasis are inadequate in females.

METHODS

We investigated the role of 7 variants of ACE, AGT and NOS3 and their correlation with NO(x) levels and ACE activity in hypertension susceptibility in 910 case-controls of both genders.

RESULTS

Prevalence of alleles D of ACE I/D; -6A of AGT -6G/A; -786C, 894T and 4a of NOS3 -786T/C, 894G/T and 4b/4a polymorphisms was observed in patients (P< or =0.05). The 3 genotypes-combinations containing 6+5 wild-type alleles of AGT and NOS3 were significantly less prevalent in patients (P< or =0.0003). The haplotypes 235T/174T/-6A of AGT (P=4E-3) and -786T/894G/4a and -786C/894G/4a of NOS3 (P=2E-3, P=0.011, respectively) were significantly more prevalent in patients. The AGT and NOS3 findings were similar in males. Genotypes-combinations with 6+5 wild-type alleles of AGT correlated with higher NO(x) levels (P=0.03). The NOS3 genotypes-combinations having 6 and 6+5 wild-type alleles correlated with decreased ACE activity (P=0.025, P=0.0015, respectively) and increased NO(x) levels (P=0.001, P=0.0001, respectively) in patients. In gene-gene interactions, ACE D allele associated with < or =4 wild-type alleles containing genotypes-combinations of AGT and NOS3 in patients (P< or =0.04).

CONCLUSION

Within gene and between genes interactions of variants influence ACE activity and NO(x) levels and associate with EH.

Drugs for the perioperative control of hypertension: current issues and future directions

The management of hypertension continues to pose important challenges. Recent developments have established the importance of more rigorous blood pressure control in the community. In the perioperative setting, hypertension has long been recognised as undesirable, although the adverse impact of high blood pressure on the acute risks of elective surgery may have been previously overstated.A number of agents and techniques are available to control blood pressure perioperatively. These include principally general and regional anaesthetics, alpha(2)-adrenoceptor agonists, peripheral alpha(1)- and beta-adrenoceptor antagonists, dihydropyridine calcium channel antagonists, dopamine D(1A)-receptor agonists (fenoldopam), and nitric oxide donors. Recent years have seen important developments in the receptor selectivity of new compounds and in pharmacokinetics, particularly esterase metabolism. The future study of genomics may enable us to identify patients at risk for hypertension-related adverse events and target therapies most effectively to these high-risk groups.

Sex-specific effects of ACE I/D and AGT-M235T on pulse pressure: the HyperGEN Study

Evidence shows that an elevated pulse pressure (PP) may lead to an increased risk of cardiovascular morbidity and mortality. There is also evidence that PP is a sexually dimorphic trait, and that genetic factors influence inter-individual variation in PP. The aim of this project was to assess the genotype-by-sex interaction on PP in a sample of mostly hypertensive African American and White participants using candidate genes involved in the renin-angiotensin-aldosterone system. Subjects were participants in the HyperGEN Study, including men (43%) and women (57%) over the age of 55 years (mean age = 65). Candidate gene polymorphisms used were ACE insertion/deletion (1,789 subjects genotyped) and AGT-M235T (1,800 subjects genotyped). We employed linear regression methods to assess the genotype-by-sex interaction. For ACE, genotype-by-sex interaction on PP was detected (P = 0.04): the "D/D" genotype predicted a 2.2 mmHg higher pulse pressure among women, but a 1.2 mmHg lower PP among men, compared to those with an "I" allele, after adjusting for age, weight, height, ethnicity, and antihypertension medication use. A similar interaction was found for systolic blood pressure. The genotype-by-sex interaction was consistent across ethnicity. The interaction was evident among those on antihypertensive medications (P = 0.05), but not among those not taking such medications (P = 0.55). In our analysis of AGT, no evidence of a genotype-by-sex interaction affecting PP, SBP, or DBP was detected. This evidence for a genotype-by-sex interaction helps our understanding of the complex genetic underpinnings of blood pressure phenotypes.

Angiotensinogen gene polymorphism (Met235Thr) influences visceral obesity and insulin resistance in obese Japanese women

To investigate the relationship between angiotensinogen (AGT) Met235Thr polymorphism (M235T) and human obesity, because AGT is regarded as one of the cytokines produced from adipocytes and serum AGT concentrations are reported to be positively correlated with body mass index. One hundred and twenty obese Japanese women (age, 58.8+/-9.4 years; body mass index, 32.2+/-4.9 kg/m(2)) were enrolled. Angiotensinogen genotypes were determined with a fluorescent allele-specific DNA primer assay system. Subjects were divided into M/M, M/T, and T/T groups. Control subjects comprised 146 healthy age-matched women. Clinical characteristics and the effects of diet and exercise therapy for 6 months were compared among the 3 genotypes. The genotype frequencies of AGT M235T polymorphism were in accordance with the Hardy-Weinberg equation (obese: M/M, 6.7%; M/T, 27.5%; T/T, 65.8%; control: M/M, 6.8%; M/T, 21.2%; T/T, 71.9%). The frequency of the T allele did not differ between obese and control subjects (0.80 vs 0.83). As the number of obese women with M/M genotype was only 8, comparisons of the characteristics and outcomes of weight reduction therapy were performed only between subjects with M/T genotype and T/T genotype. In the T/T group, % body fat and waist circumference at baseline were significantly greater than in the M/T group (36.3%+/-4.8% vs 33.8%+/-4.7%, P=.0105; 107.9+/-10.9 vs 102.6+/-7.9 cm, P=.0428, respectively). Before the weight reduction therapy, significantly higher insulin and higher homeostasis model assessment (HOMA-R) were demonstrated in the T/T group than in the M/T group (9.1+/-5.5 microU/mL vs 5.9+/-4.4 microU/mL, P=.0056; 2.3+/-1.4 vs 1.6+/-1.3, P=.0252, respectively). Both systolic and diastolic blood pressure at baseline in the T/T group tended to be higher than those in the M/T group, but the differences were not significant. No genotype-dependent difference in energy expenditure or outcome of weight reduction therapy was observed with respect to AGT M235T polymorphism. After the diet and exercise therapy, the blood pressure in the T/T group tended to be higher than that in the M/T group, but the difference was not significant. We demonstrated that the T/T genotype of the AGT M235T gene polymorphism was positively related to visceral obesity and hyperinsulinemia in obese Japanese women. Blood pressure did not show genotype-specific differences before or after the treatment. Further studies of the association between obesity and this gene polymorphism should contribute to understanding and treating obesity-related diseases.

Angiotensinogen M235T gene variants and its association with essential hypertension and plasma renin activity in Malaysian subjects: a case control study

BACKGROUND

Essential hypertension is a major public health concern worldwide where its prevalence accounts for various cerebrovascular diseases. A common molecular variant of angiotensinogen (AGT), the precursor of potent vasoactive hormone angiotensin II, has been incriminated as a marker for genetic predisposition to essential hypertension in some ethnics. This case-control study was designed not only to determine the association of the AGT M235T gene variants with essential hypertension, but also its relationship to Plasma Renin Activity (PRA) in subjects attending the Health Clinic, Kuala Lumpur, Malaysia.

METHODS

The study involved 188 subjects, 101 hypertensives and 87 normotensives. Consents were obtained from all the participated subjects. M235T gene variants were investigated using allele specific polymerase chain reaction and PRA was determined by radioimmunoassay. Hypertensinogenic factors such as dietary habits, physical activity, smoking and drinking habits were assessed using a pre-tested questionnaire.

RESULTS

The genotype and allele distribution of the M235T variant differed significantly in hypertensives and normotensives (chi2 = 23.184, P < 0.001 and chi2 = 21.482, P < 0.001, respectively). The odds ratio for hypertension was 1.36 (95% confidence interval 1.03-1.80) for subjects with homozygous mutated allele TT of the M235T variant compared with other genotypes or 1.98 (95% confidence interval 1.46-2.67) for those carrying T allele compared to those carrying M allele. Plasma Renin Activity is also significantly higher in hypertensive subjects (PRA = 3.8 +/- 2.5 ngAI/ml/hr for hypertensives, PRA = 2.6 +/- 1.3 ngAI/ml/hr for normotensives, P < 0.001), but was not significantly different between groups of genotypes (P = 0.118).

CONCLUSION

The M235T variant of the AGT is significantly associated with essential hypertension whereas the genotype TT or allele T is a possible genetic marker or risk factor for hypertension in Malaysian subjects.

Polymorphisms of the insertion / deletion ACE and M235T AGT genes and hypertension: surprising new findings and meta-analysis of data

Background

Essential hypertension is a common, polygenic, complex disorder resulting from interaction of several genes with each other and with environmental factors such as obesity, dietary salt intake, and alcohol consumption. Since the underlying genetic pathways remain elusive, currently most studies focus on the genes coding for proteins that regulate blood pressure as their physiological role makes them prime suspects.

The present study examines how polymorphisms of the insertion/deletion (I/D) ACE and M235T AGT genes account for presence and severity of hypertension, and embeds the data in a meta-analysis of relevant studies.

Methods

The I/D polymorphisms of the ACE and M235T polymorphisms of the AGT genes were determined by RFLP (restriction fragment length polymorphism) and restriction analysis in 638 hypertensive patients and 720 normotensive local blood donors in Weisswasser, Germany. Severity of hypertension was estimated by the number of antihypertensive drugs used.

Results

No difference was observed in the allele frequencies and genotype distributions of ACE gene polymorphisms between the two groups, whereas AGT TT homozygotes were more frequent in controls (4.6% vs. 2.7%, P = .08). This became significant (p = 0.035) in women only. AGT TT genotype was associated with a 48% decrease in the risk of having hypertension (odds ratio: 0.52; 95% CI, 0.28 to 0.96), and this risk decreased more significantly in women (odds ratio: 0.28; 95% CI, 0.1 to 0.78). The meta-analysis showed a pooled odds ratio for hypertension of 1.21 (TT vs. MM, 95% CI: 1.11 to 1.32) in Caucasians. No correlation was found between severity of hypertension and a specific genotype.

Conclusion

The ACE I/D polymorphism does not contribute to the presence and severity of essential hypertension, while the AGT M235T TT genotype confers a significantly decreased risk for the development of hypertension in the population studied here. This contrasts to the findings of meta-analyses, whereby the T allele is associated with increased risk for hypertension.

Angiotensinogen promoter haplotypes are associated with blood pressure in untreated hypertensives

BACKGROUND

The polymorphic angiotensinogen (AGT) gene is one of the most promising candidates for blood pressure (BP) regulation and essential hypertension.

OBJECTIVES

To investigate whether AGT haplotype analysis adds significant information compared to single polymorphism analysis with respect to different BP phenotypes in an untreated hypertensive sample.

METHODS

Two hundred and twelve untreated hypertensive subjects of Caucasian origin were genotyped for the AGT polymorphisms C-532T, A-20C, C-18T, and G-6A.

RESULTS

In single variant analyses, untreated hypertensives, carrying the AGT -532T or -6A alleles had significantly higher systolic blood pressure (SBP) and diastolic blood pressure (DBP), as well as ambulatory BP values compared to respective non-carriers. In haplotype-based analyses, combining all four AGT promoter variants, we demonstrate that AGT haplotypes containing different allele combinations at positions -532 and -6 were significantly associated with different BP values: (1) -532T and -6A with higher, (2) -532C and -6G with lower, (3) -532C and -6A with intermediate BP values. Since the result for the -532C/-20A/-18C/-6G haplotype was due to differences between non-carriers and carriers of this haplotype on both chromosomes, a recessive inheritance model for BP effects could be assumed.

CONCLUSIONS

Our results designate the C-532T and G-6A as the best candidates for functional studies on the AGT gene. Haplotype-based analyses should greatly aid in the dissection of the genetic basis of complex traits, such as BP regulation and hypertension.

Long-term effects of quinapril with high affinity for tissue angiotensin-converting enzyme after coronary intervention in Japanese

BACKGROUND

Angiotensin-converting enzyme inhibitors have been shown experimentally to prevent restenosis after balloon injury. We previously reported that quinapril reduced the 6-month restenosis (percent diameter stenosis >or=50%) rate after percutaneous coronary intervention (PCI). However, it was not established whether this favorable outcome was maintained for longer periods.

METHODS

This study was a prospective, randomized, open, and non-placebo controlled trial. Patients with coronary artery disease were enrolled after successful coronary balloon angioplasty or stenting. Two hundred and fifty-three patients were randomly assigned to the quinapril (10-20 mg per day) or control groups. The major clinical end points included death, myocardial infarction, cerebrovascular accident, or revascularization (either coronary artery bypass grafting or repeat PCI). These were tabulated according to the intention-to-treat principle.

RESULTS

Long-term follow-up was available with a median of 4.8 (interquartile range 4.2-5.1) years after the procedure. The incidence of combined end points of mortality and morbidity (myocardial infarction and cerebrovascular accident) in the quinapril group was lower than that in the control group (6.1% vs 14.8%; relative risk [RR] 0.42, 95% CI 0.18-0.96, P =.033). The overall incidence of end-point events in patients with quinapril also occurred less frequently (29.8% vs 46.7%; RR 0.58, 95% CI 0.38-0.86, P =.007).

CONCLUSIONS

These clinical outcomes show that the benefit of quinapril in patients following PCI is maintained for 4 years.

Coronary heart disease, hypertension, and angiotensinogen gene variants in Indian population

Gene encoding components of the renin angiotensin system (RAS) have been implicated with the increased risk of cardiovascular disease (CVD). Two variants of the angiotensinogen (AGT) gene, M235T and T174M, have been shown to be associated with increased risk of hypertension. In the present study, we examined the association of these two polymorphisms and their synergistic interaction with the angiotensin I-converting enzyme (ACE) deletion homozygote genotype (D/D) on subjects with coronary heart disease (CHD) and hypertension. We studied 131 healthy individuals, 141 angiographically verified CHD patients, and 159 hypertensive subjects. The identification of the ACE and AGT gene polymorphisms was carried out using a PCR-based restriction endonuclease digestion method. There was no significant difference in the distribution of the M235T and T174M variants between the two test groups and the control group. Association was also not seen when analysis was carried out in patients when subgrouped according to the extent of the severity of the disease. In addition, the risk was not restricted to subjects carrying the D allele of the ACE gene and T235T of AGT. M235T and T174M variants do not contribute to the increased risk of CHD or hypertension in the Indian population.

Detection of putative functional angiotensinogen (AGT) gene variants controlling plasma AGT levels by combined segregation-linkage analysis

Previous studies have suggested that angiotensinogen (AGT) gene variants are associated with increased plasma AGT levels, and may also contribute towards the inherited component of predisposition to essential hypertension in humans. To explore the potential functionality of several AGT polymorphisms and estimate their effects, together with other sources of familial correlations, on plasma AGT, we undertook a large study involving 545 healthy French volunteers in 130 nuclear families that include 285 offspring. Plasma AGT levels were measured in all participants, and bi-allelic AGT variants were analysed as candidate functional variants at three sites in the 5'-flanking region (C-532T, A-20C, G-6A), two sites in exon 2 (M235T, T174M) and two newly identified variant sites in the untranslated sequence of exon 5 and the 3'-flanking region (C+2054A, C+2127T) of the gene. Analysis with the class D regressive model showed significant effects influencing plasma AGT levels of all AGT polymorphisms tested, with the exception of T174M. The most significant result was found at C-532T (P=0.000001), which accounts for 4.3% of total plasma AGT variability in parents and 5.5% in offspring, with substantial residual familial correlations. Maximum likelihood estimates of haplotype frequencies and tests of linkage disequilibrium between each AGT polymorphism and a putative QTL are in agreement with a complete confounding of C-532T with the QTL, when taking into account sex and generation specific effects of the QTL. However, further combined segregation-linkage analyses showed significant evidence for additional effects of G-6A, M235T and C+2054A polymorphisms after accounting for C-532T, which supports a complex model with at least two functional variants within the AGT gene controlling AGT levels.

An association of BMI with A (-6) G, M235T and T174M polymorphisms in angiotensinogen gene in essential hypertension

The aim of the study was to assess the existence of possible associations among frequent polymorphisms in angiotensinogen genes and some of the risk factors for essential hypertension, especially body mass index (BMI) and smoking. A total of 192 control subjects (aged 45.87 +/- 3.0 years) and 206 patients with the essential hypertension (aged 48.71 +/- 8.42 years) were compared at three angiotensinogen gene polymorphisms by considering BMI and smoking status. No significant differences in genotype and/or allelic distribution for either A (-6) G ATG, M235T or T174M polymorphisms between the hypertensive and control groups were proved. Significantly more hypertensives than control persons with BMI above 25 kg/m(2) were observed (P(corr) = 0.009), independently on sex distribution. A percentage of 44.6% of smokers in the control group vs 46.0% of smokers in the hypertensive groups were found. No significant difference in concurrence of BMI above 25 kg/m(2) and positive smoking status between control and hypertensive subjects was found. Statistically significant differences were found between control and hypertensive subjects when compared distributions of subjects with certain genotypes of the three examined polymorphisms considering BMI (P(corr) = 0.0002 for AA+AG of A (-6) G ATG, P(corr) = 0.01 for CC + CT of T(174)M ATG and P(corr) = 0.01 for MT + TT of M235T ATG). No functional relationship among obesity and the examined polymorphisms in vivo are known. We conclude that a different distribution of BMI could influence the results of analyses of angiotensinogen gene polymorphisms in essential hypertension-control studies.

Coronary artery disease and dyslipidemia within Europe: genetic variants in lipid transport gene loci in German subjects with premature coronary artery disease

Fifteen polymorphisms in six lipid transport genes were studied in a German population for relationships with dyslipidemia and coronary artery disease (CAD), to investigate a possible genetic basis for the marked differences in mortality rates from coronary heart disease within Europe. In other populations these polymorphisms have all been associated with CAD or with phenotypes known to predispose to CAD. The apoAI PstI polymorphism (P<0.005) and the lipoprotein lipase Ser(447)-Ter mutation (P<0.005) were associated with plasma triglyceride concentrations. Additionally, the apoAI PstI polymorphism (P<0.05), the apoB XbaI polymorphism (P<0.05) and apoE phenotypes (P<0.05) were associated with plasma cholesterol concentrations. However, none of the allele frequencies of the polymorphisms studied were related to the presence, or absence, of coronary artery disease. Associations between five polymorphisms representing four lipid transport gene loci and dyslipidemia were demonstrated in this German population. It is possible that predisposition to dyslipidemia in Germany involves a particular selection of polymorphic loci, which are different from those identified in other European countries.

Power and replication in case-control studies

The case-control study design, a common staple of epidemiology, is increasingly used to test for genetic association. The simplicity of the design accounts for both its appeal and its limitations. Too often, however, apparent controversy arises for lack of appreciation of basic tenets underlying statistical testing. Power and replication are two concepts most commonly ignored in evaluating such studies. We review the basic principles of statistical testing, recall simple means to calculate power, and provide numerical examples pertaining to the association between angiotensinogen and essential hypertension.

Angiotensinogen T174M and M235T variants, sodium intake and hypertension among non-drinking, lean Japanese men and women

OBJECTIVE

To examine the interaction of sodium intake with genetic variations of the angiotensinogen gene and hypertension.

DESIGN

A community-based case-reference study.

SETTING

Two rural Japanese communities.

PARTICIPANTS

Non-overweight and non-drinking Japanese men and women: 229 hypertensives and 229 age-, sex- and community-matched normotensives aged 32 to 83 years.

METHODS

Polymorphisms of the angiotensinogen gene detected by an allele-specific polymerase chain reaction. A priori hypothesis is individuals with 174M (threonine-to-methionine substitution) or 235T (methionine-to-threonine substitution) allelic variations may have an elevated risk of hypertension when they have a high sodium intake, estimated by 24-h urine collection and a dietary questionnaire.

RESULTS

The genotypic frequency of the haplotype including both the 174M and 235T alleles was higher among hypertensives than among normotensives (23 versus 14%, P= 0.02). The frequency of the 174M allele was specifically higher among hypertensives than normotensives (12 versus 7%, P=0.01), and the odds ratio of hypertension associated with the 174M (versus 174T) allele was 1.8 [95% confidence interval (CI) 1.1-3.0, P=0.01]. The frequency of the 235T allele did not vary between the two groups (80 versus 82%, P= 0.40). The relationship between the 174M allele and hypertension was more evident among persons who had higher urinary sodium excretion (> = 166 mmol/day) than those with lower excretion (< 166 mmol/day): odds ratio 2.5 (95% CI, 1.2-5.2), P=0.01 versus 1.5 (95% CI, 0.7-3.1), P= 0.31; P for interaction = 0.04, and this trend was primarily observed for early-onset hypertension (< 55 years at onset). A similar but nonsignificant association was observed when stratified using present and past sodium intake scores derived from questionnaires.

CONCLUSION

Angiotensinogen genotype may affect the development of early-onset hypertension among Japanese, particularly in those who have a high sodium intake.

[Role of the angiotensinogen gene for essential hypertension]

Essential hypertension is a complex disease influenced by different genetic and environmental factors. The renin-angiotensin system (RAS) is implicated in blood pressure regulation. Angiotensinogen (AGT) is the precursor of the biologically active angiotensin II (Ang II). Initial studies on hypertensive siblings and case-control studies indicated the important role of the angiotensinogen gene (AGT) for the predisposition to essential hypertension, preeclampsia and obesity-related hypertension. Recently, different AGT polymorphisms had been identified and analyzed in case-control studies. The aim of present studies is the analysis of potentially functional AGT variants (C-532T, G-6A), which might be responsible for the regulation of gene expression and therefore AGT generation. The A-6 allele is in complete linkage disequilibrium with the T235 allele and is associated with higher AGT expression in vitro. Segregation linkage analysis demonstrated that the C-532T polymorphism influences plasma AGT variability more significantly than the G-6A variant. Since the C-532T polymorphism is located within a AP-2 consensus element, functional promoter analyses are required. The understanding of the molecular basis of RAS in essential hypertension may provide us with new and more specific pharmacological agents and perhaps the ability to individualize antihypertensive treatment.

The L10F mutation of angiotensinogen is rare in pre-eclampsia

BACKGROUND

A mutation in the gene for angiotensinogen, changing the leucine residue at position 10 to a phenylalanine (L10F), has been reported in a patient with proteinuric pre-eclampsia. In vitro enzymatic studies suggest this mutation would increase production of the vasoactive peptide, angiotensin II in vivo, and therefore explain the etiology of the maternal hypertension.

OBJECTIVE

To determine whether mutation of codon 10 of angiotensinogen is common in pre-eclampsia, and therefore likely to be involved in disease susceptibility.

DESIGN

We collected a cohort of 32 women with 'true' pre-eclampsia. All were normotensive prior to the 20th week of pregnancy, developed blood pressures consistently above 140/90 mmHg and had proteinuria of greater than 300 mg/day during the third trimester. All had blood pressures that returned to normal within 1 month of delivery; 31 women were primigravida. Genomic DNA was isolated from their peripheral blood lymphocytes for genetic analyses.

METHODS

A polymerase chain reaction-restriction enzyme-based assay was devised to screen for mutation of codon 10 of the angiotensinogen gene. In addition, we determined the frequency of a threonine residue at position 235 in the angiotensinogen gene, given previous controversial findings of association of this polymorphism with disease.

CONCLUSIONS

We detected no mutation of codon 10 in angiotensinogen in any of the 32 women studied, indicating that this mutation is not commonly associated with proteinuric pre-eclampsia. Furthermore, there was no increased frequency of threonine 235 in the affected individuals studied compared with respective normotensive Caucasian-American and African-American populations.

Appropriate tissue- and cell-specific expression of a single copy human angiotensinogen transgene specifically targeted upstream of the HPRT locus by homologous recombination

Development of experimental models by genetic manipulation in mice has proven to be very useful in determining the significance of particular genes in the development of or susceptibility to hypertension. Advances in molecular genetics, transgenic mouse technology, and physiological measurements in mice provided an opportunity to go a step further and develop models to analyze the physiological significance of specific gene variants potentially causing hypertension. In this report, we describe the development of a human angiotensinogen transgenic mouse model generated by targeting the human angiotensinogen gene upstream of the mouse HPRT locus by homologous recombination. The main benefit of this transgenic mouse model is that the human angiotensinogen gene is inserted into the mouse genome as a single copy at a predefined locus and in a specific orientation-a process that can be repeated utilizing other variants of this gene. We establish the validity of this approach by showing that the hAGT(hprt) mice have normal tissue- and cell-specific expression of the human angiotensinogen gene and normally produce and process the hAGT protein at physiological levels.

Renin-angiotensin-aldosterone system gene polymorphisms and hypertension in Hong Kong Chinese

In Chinese populations, hypertension is common and is a major risk factor for cerebrovascular and coronary heart disease. The renin-angiotensin-aldosterone system (RAAS) helps maintain blood pressure and salt homeostasis and appears important in the pathogenesis of hypertension and some forms of vascular disease. We investigated three RAAS gene polymorphisms, the angiotensin-converting enzyme (ACE) insertion/deletion, angiotensinogen (AGT) M235T and angiotensin II type 1 receptor A1166C polymorphisms in 232 hypertensive and 178 normotensive Chinese subjects. The hypertensives were generally more obese and dyslipidaemic. No significant differences in genotype or allele frequencies for any of the polymorphisms were identified between the groups, nor was there any interactive contribution to blood pressure by the ACE and AGT polymorphisms. However, there were large differences in genotype and allele frequencies between the healthy Chinese and published data for equivalent Caucasian populations. These findings suggest these polymorphisms are unlikely to be involved in the pathogenesis of hypertension in Chinese.

Exclusion of angiotensinogen gene in molecular basis of human hypertension: sibpair linkage and association analyses in Australian anglo-caucasians

Linkage with essential hypertension has been claimed for a microsatellite marker near the angiotensinogen gene (AGT; chromosome 1q42), as has association for the AGT variants M235T, G(-6)A and A(-20)C. To more rigorously evaluate AGT as a candidate gene for hypertension we performed sibpair analysis with multiple microsatellite markers surrounding this locus and using more sophisticated analysis programs. We also performed an association study of the AGT variants in unrelated subjects with a strong family history (two affected parents). For the linkage study, single and multiplex polymerase chain reaction (PCRs) and automated genescan analysis were conducted on DNA from 175 Australian Anglo-Celtic Caucasian hypertensives for the following markers: D1S2880-(2.1 cM)-D1S213-(2.8 cM)-D1S251-(6.5 cM)-AGT-(2.0 cM) -D1S235. Statistical evaluation of genotype data by nonparametric methods resulted in the following scores: Single-point analysis - SPLINK, P > 0.18; APM method, P > 0.25; ASPEX, MLOD < 0.28; SIB-PAIR, P > 0. 24; Multipoint analysis - MAPMAKER/SIBS, MLOD < 0.24; GENEHUNTER, P > 0.35. Exclusion scores of Lod -4.1 to -5.1 were obtained for these markers using MAPMAKER/SIBS for a lambda(s) of 1.6. The association study of G(-6)A, A(-20)C and M235T variants in 111 hypertensives with strong family history and 190 normotensives with no family history showed significant linkage disequilibrium between particular haplotypes, but we could find no association with hypertension. The present study therefore excludes AGT in the etiology of hypertension, at least in the population of Australian Anglo-Celtic Caucasians studied.

Polymorphism in the angiotensin converting enzyme but not in the angiotensinogen gene is associated with hypertension and type 2 diabetes: the Skaraborg Hypertension and diabetes project

OBJECTIVE

To study the association between polymorphisms in the angiotensin converting enzyme (ACE) gene and angiotensinogen (AGT) gene and hypertension and/or type 2 diabetes in a community population.

PATIENTS AND METHODS

The insertion (I)/deletion (D) polymorphism of the ACE gene and the M235T polymorphism of the AGT gene were genotyped in 773 nondiabetic individuals with hypertension, 193 normotensive patients with type 2 diabetes, 243 patients with type 2 diabetes and hypertension, and in 820 normotensive control individuals identified in a community-based study.

RESULTS

The DD genotype was associated with hypertension in individuals less than 70 years [odds ratio (OR) = 1.54, confidence interval (CI) = 1.09-2.18] and remained so when patients with type 2 diabetes were excluded from the analysis (OR = 1.45, CI = 1.01-2.09). The strongest association was with the combination of type 2 diabetes and hypertension (OR = 2.19, CI = 1.09-4.38). There was no association with type 2 diabetes without hypertension. No association was observed between the M235T variant or the 3'-microsatellite polymorphism of the AGT gene and hypertension.

CONCLUSION

The D-allele of the ACE gene ID polymorphism increases susceptibility to hypertension, particularly when associated with type 2 diabetes. No association was observed between the M235T variant or 3'-microsatellite polymorphism of the AGT gene and hypertension.

Associations of the angiotensinogen gene (M235T, T174M) and the angiotensin I-converting enzyme gene (I/D) with blood pressure in Japanese workers

Blood pressure may be influenced by several polymorphisms associated with hypertension, such as the angiotensinogen gene (M235T, T174M) and the angiotensin I-converting enzyme gene (I/D). We investigated the associations of these polymorphisms with blood pressure and components of the renin-angiotensin system in Japanese workers. Additionally, we examined whether the polymorphisms were independently associated with blood pressure when other factors were taken into consideration in a general linear model. The study population, which was entirely Japanese, consisted of 196 male subjects. Subjects were selected from workers who received a company health examination. Systolic blood pressure of the M235T MM genotype was significantly higher than that of the MT genotype. Diastolic blood pressure of the M235T MM genotype was significantly higher than that of the MT or TT genotypes. Serum ACE activity of the ACE II genotype was significantly lower than that of the ID or DD genotypes. Multivariate analysis using a general linear model, including age and body mass index, demonstrated that the M235T MM genotype was one of the independent factors affecting blood pressure. The present study demonstrated that the M235T MM genotype was independently associated with systolic blood pressure and diastolic blood pressure in Japanese male workers.

Angiotensinogen gene and essential hypertension in the Japanese: extensive association study and meta-analysis on six reported studies

BACKGROUND

Accumulating evidence has supported the pathophysiological role of angiotensinogen in essential hypertension. However, some studies of molecular genetics have implicated that there may be an ethnic variation concerning the disease susceptibility of the AGT gene.

OBJECTIVES AND METHODS

To evaluate the importance of this candidate gene for hypertension, we undertook an extensive association study in the Japanese. This case-control study was conducted in a total of 1232 individuals consecutively enrolled in a single institution, divided into two subgroups: one subgroup comprised 254 hypertensive and 224 normotensive subjects and the other comprised 463 hypertensive and 291 normotensive subjects. A meta-analysis was subsequently performed on six Japanese studies including the present study.

RESULTS

No significant association was observed between a molecular variant of AGT, Thr235, and hypertension status in our case-control study. Moreover, this finding was extendible to another AGT polymorphism, G-6A, one of the potential functional polymorphisms in the promoter region, because these two polymorphisms proved to be in complete linkage disequilibrium in the studied population. The meta-analysis revealed that the pooled estimate of the odds ratio across the studies was 1.22 (95% CI 1.05-1.42), and that there was significant evidence against homogeneity of the odds ratios among the studies included (phi2 = 19.8, df = 5, P = 0.0014). In particular, a large range of variation (60-83%) was found for the allele frequency of Thr235 among control subjects of the six Japanese case-control studies.

CONCLUSIONS

Although the meta-analysis appears in favour of association between the AGT variant and essential hypertension in the Japanese, there is considerable heterogeneity among the studies and the evidence is also rather borderline. Further comprehensive approaches are needed to resolve this debatable issue.

Angiotensinogen M235T polymorphism is associated with plasma angiotensinogen and cardiovascular disease

BACKGROUND

Genes encoding components of the renin-angiotensin system have been associated with elevated blood pressure (BP) and an increased risk of coronary artery disease. To explore the role of the angiotensinogen (AGT) gene in coronary atherosclerosis and thrombosis, we studied the effect of the AGT M235T gene variant on plasma AGT levels and BP in patients with coronary artery disease and in the subgroup of survivors of myocardial infarction as compared with angiographically defined control subjects.

METHODS AND RESULTS

This was a case-control study of 301 white male subjects examined at Frankfurt University medical center. Plasma AGT levels increased stepwise according to the number of T235 alleles present (no T235 allele, 14.8 +/- 3.9 nmol/L; 1 allele, 15.7 +/- 5.1 nmol/L; 2 alleles, 17.3 +/- 4.7 nmol/L; P =.006). In a multivariate model, circulating AGT emerged as the most important predictor of diastolic pressure (P =.001). In addition, AGT M235T gene polymorphism remained a significant predictor of diastolic BP in a multivariate model adjusted for age, body mass index, fasting glucose, apolipoprotein B, presence of coronary artery disease, and treatment with antihypertensive agents ( P <.05). Finally, homozygosity for T235 was associated with increased univariate risk of coronary artery disease and myocardial infarction (odds ratio estimates 1.5; 95% confidence intervals 1.1 to 2.1, P =.03, and 1.0 to 2.1, P =.05, respectively).

CONCLUSIONS

The significant relations observed between the AGT M235T variant, its protein product, and the cardiovascular disease phenotypes provide evidence for a possible role of elevated circulating AGT in the pathogenesis of coronary artery disease.

Angiotensinogen variants and human hypertension

The research on molecular genetics of human hypertension aims to identify the loci involved in the regulation of blood pressure, detect gene variants within the identified loci, associate them with intermediate phenotypes, and ultimately estimate their quantitative effects on blood pressure level and their interaction with main environmental factors. So far, the angiotensinogen (AGT) gene is one of the few candidate genes that has been investigated using these multiple statistical, clinical, and biochemical strategies. A highly polymorphic dinucleotide GT repeat (80% heterozygosity) has been used in several linkage studies. Other diallelic polymorphisms, located in the 5' regulatory region of the gene in intronic and exonic sequences, have been described, which were then used in association studies in different clinical settings. Positive associations between the M235T and the G-6A polymorphisms and plasma angiotensinogen levels indicates a pathway by which the AGT locus could be involved in essential hypertension.

Ionizing radiation and genetic risks. VI. Chronic multifactorial diseases: a review of epidemiological and genetical aspects of coronary heart disease, essential hypertension and diabetes mellitus

This paper provides a broad overview of the epidemiological and genetical aspects of common multifactorial diseases in man with focus on three well-studied ones, namely, coronary heart disease (CHD), essential hypertension (EHYT) and diabetes mellitus (DM). In contrast to mendelian diseases, for which a mutant gene either in the heterozygous or homozygous condition is generally sufficient to cause disease, for most multifactorial diseases, the concepts of genetic susceptibility' and risk factors' are more appropriate. For these diseases, genetic susceptibility is heterogeneous. The well-studied diseases such as CHD permit one to conceptualize the complex relationships between genotype and phenotype for chronic multifactorial diseases in general, namely that allelic variations in genes, through their products interacting with environmental factors, contribute to the quantitative variability of biological risk factor traits and thus ultimately to disease outcome. Two types of such allelic variations can be distinguished, namely those in genes whose mutant alleles have (i) small to moderate effects on the risk factor trait, are common in the population (polymorphic alleles) and therefore contribute substantially to the variability of biological risk factor traits and (ii) profound effects, are rare in the population and therefore contribute far less to the variability of biological risk factor traits. For all the three diseases considered in this review, a positive family history is a strong risk factor. CHD is one of the major contributors to mortality in most industrialized countries. Evidence from epidemiological studies, clinical correlations, genetic hyperlipidaemias etc., indicate that lipids play a key role in the pathogenesis of CHD. The known lipid-related risk factors include: high levels of low density lipoprotein cholesterol, low levels of high density lipoprotein cholesterol, high apoB levels (the major protein fraction of the low density lipoprotein particles) and elevated levels of Lp(a) lipoprotein. Among the risk factors which are not related to lipids are: high levels of homocysteine, low activity of paraoxonase and possibly also elevated plasma fibrinogen levels. In addition to the above, hypertension, diabetes and obesity (which themselves have genetic determinants) are important risk factors for CHD. Among the environmental risk factors are: high dietary fat intake, smoking, stress, lack of exercise etc. About 60% of the variability of the plasma cholesterol is genetic in origin. While a few genes have been identified whose mutant alleles have large effects on this trait (e.g., LDLR, familial defective apoB-100), variability in cholesterol levels among individuals in most families is influenced by allelic variation in many genes (polymorphisms) as well as environmental exposures. A proportion of this variation can be accounted for by two alleles of the apoE locus that increase (&epsi;4) and decrease (&epsi;2) cholesterol levels, respectively. A polymorphism at the apoB gene (XbaI) also has similar effects, but is probably not mediated through lipids. High density lipoprotein cholesterol levels are genetically influenced and are related to apoA1 and hepatic lipase (LIPC) gene functions. Mutations in the apoA1 gene are rare and there are data which suggest a role of allelic variation at or linked LIPC gene in high density lipoprotein cholesterol levels. Polymorphism at the apoA1--C3 loci is often associated with hypertriglyceridemia. The apo(a) gene which codes for Lp(a) is highly polymorphic, each allele determining a specific number of multiple tandem repeats of a unique coding sequence known as Kringle 4. The size of the gene correlates with the size of the Lp(a) protein. The smaller the size of the Lp(a) protein, the higher are the Lp(a) levels. (ABSTRACT TRUNCATED)

M235T angiotensinogen gene polymorphism and cardiovascular renal risk

OBJECTIVE

In this meta-analysis, we attempted to derive pooled estimates for the putative associations between various cardiovascular-renal disorders and the M235T polymorphism of the angiotensinogen gene.

METHODS

Case-control studies were combined, using the Mantel and Haenszel approach. Joint P values for continuous variables were calculated by Stouffer's method. Continuous measurements reported in different units were expressed on a percentage scale using the intrastudy mean of the MM genotype as denominator.

RESULTS

The computerized database used for this analysis included 69 reports with an overall sample size of 27,906 subjects. Overall, possession of the T allele was associated with an increased risk of hypertension. In comparison with the MM reference group (number of studies, n = 32), the excess risk was 31% (P = 0.001) in TT homozygotes and 11% (P = 0.03) in TM heterozygotes. The sensitivity analysis showed that this association was present only in whites (T allelic frequency, f = 42.2%), but not in blacks (f = 77.0%) or Asians (f = 78.0%). Atherosclerotic complications (n = 12), renal microvascular disorders (n = 13), cardiomyopathy (n = 2) or diabetic retinopathy (n = 3) were not correlated with the M235T polymorphism. Publication bias was observed for hypertension, but not for coronary heart disease, including myocardial infarction, and for microvascular nephropathy. Furthermore, in comparison with the MM control group, the circulating angiotensinogen levels (n = 8) were raised by 11 and 7% (P = 0.01) in TT and TM subjects, respectively. In contrast, plasma levels of the angiotensin I converting enzyme (n = 4) and body mass index (n = 15) were not associated with the T allele.

CONCLUSION

The T allele encoding angiotensinogen is not associated with atherosclerotic or microvascular complications, but in Caucasians behaves as a marker for hypertension. This association, which may have been inflated by publication bias, does not necessarily imply causality.

Associations of angiotensinogen gene mutations with hypertension and myocardial infarction in a gulf population

To date, the human angiotensinogen (AGT) gene and some of its variants represent the best examples of genetic influences that are involved in the determination of essential hypertension (EH) and associated cardiovascular diseases (CVDs). To assess the value of genotyping AGT in a genetically homogeneous population, we carried out a retrospective, case control study of variants M235T and T174M for putative correlations with CVDs among nationals from the United Arab Emirates (Emirati)--an ethnic group characterized by no alcohol intake and no cigarette smoking. We investigated a sample population of 229 Emirati (119 males and 110 females), comprising groups of controls and patients with clinical diagnoses of EH, left ventricular hypertrophy (LVH), ischaemic heart disease (IHD) and myocardial infarction (MI). M235T and T174M alleles were determined via assays based on the polymerase chain reaction. T174M showed no correlation with any of the four clinical entities included in this study. T235 alleles, however, occurred more frequently in the EH group and less frequently in the group of MI survivors. We also found that T235 allele frequencies decreased with age, indicating that in the Emirati population, T235 alleles are associated with a reduced life span and that this effect could occur through independent mechanisms underlying genetic susceptibilities to both EH and MI.

Transgenesis and Gene Targeting in the Mouse

As more effort is made to identify genes responsible for hypertension in human populations and genetically hypertensive animal models, the need for experimental systems in which the functional significance of genes, gene variants, and quantitative trait loci (QTL) can be determined is becoming increasingly important. Over the past five years, transgenic and gene-targeting technology has been utilized to study the cardiovascular effects of over-expression or ablation of genes which have been considered candidates in the genetic basis of hypertension. This review focuses on the most recent major advances in this area, and how this technology aids in our understanding of the molecular mechanisms by which newly discovered genes or gene variants affect blood pressure in the whole organism. We also discuss the potential use of transgenic models in refining the location of a QTL, and discuss some of the limitations and potential pitfalls in the application of these tools to the field of hypertension research. The coupling of genetic manipulations afforded by transgenesis and gene targeting, along with advances in our ability to assess the cardiovascular phenotype in the mouse, provides us with a powerful system for examining the genes responsible for causing essential hypertension.

M235T polymorphism of the angiotensinogen gene and hypertension in Chinese

OBJECTIVES

To compare the distributions of the genotypes and alleles of the M235T polymorphism of the angiotensinogen gene for hypertensive patients and normotensive controls.

DESIGN

A study of association of genetic polymorphisms.

SETTING

An outpatient clinic run by a university department handling referrals from primary care.

PATIENTS

Two hundred and four subjects, 103 normal controls and 101 patients with newly diagnosed or documented hypertension.

METHOD

Genomic DNA was extracted from peripheral blood leucocytes, amplified by polymerase chain reaction and digested with the restriction enzyme Tth 111 I. Methionine (M) and threonine (T) alleles were identified after electrophoresis.

MAIN OUTCOME MEASURES

Prevalences of angiotensinogen genotypes and alleles for hypertensive patients and controls.

RESULTS

MM, TM and TT genotypes occurred in 3, 24 and 73% of controls and 1, 22 and 77% of hypertensive patients, respectively. The prevalences of the M and T alleles were 0.15 and 0.85 among controls and 0.12 and 0.88 among hypertensive patients. The prevalences of the angiotensinogen genotypes and alleles for controls and hypertensive patients did not differ significantly.

CONCLUSIONS

Our findings differed from previous reports and suggested that this polymorphism is not associated with hypertension in this population.

Hypertension: genes and environment

Hypertension can be classified as either Mendelian hypertension or essential hypertension, on the basis of the mode of inheritance. The Mendelian forms of hypertension develop as a result of a single gene defect, and as such are inherited in a simple Mendelian manner. In contrast, essential hypertension occurs as a consequence of a complex interplay of a number of genetic alterations and environmental factors, and therefore does not follow a clear pattern of inheritance, but exhibits familial aggregation of cases. In this review, we discuss recent advances in understanding the pathogenesis of both types of hypertension. We review the causal gene defects identified in several monogenic forms of hypertension, and we discuss their possible relevance to the development of essential hypertension. We describe the current approaches to identifying the genetic determinants of human essential hypertension and rat genetic models of hypertension, and summarise the results obtained to date using these methods. Finally, we discuss the significance of environmental factors, such as stress and diet, in the pathogenesis of hypertension, and we describe their interactions with specific hypertension susceptibility genes.

The application of molecular genetic techniques to the study of hypertensive diseases

The techniques of modern molecular genetics are shedding new light on hypertension and its sequelae. This article discusses techniques which have identified genes associated with hypertension and have pointed the way toward identifying the full cohort of genes operative in all forms of human hypertension. These techniques have expanded understanding of the pathophysiology of hypertension as well as its prevention.

Angiotensinogen gene variation in a population case-control study of preeclampsia/eclampsia in Australians and Chinese

Preeclampsia/eclampsia (PE/E) is a common disease of human pregnancy with a strong genetic component. The etiology of PE/E is unknown. Two recent reports indicated that the angiotensinogen gene (AGT) could be involved in susceptibility to PE/E. We performed a population-based case-control study in Australian and Chinese populations to investigate whether AGT is a good candidate gene for PE/E. A microsatellite polymorphism within AGT was typed as well as a molecular variant T235 (Met-->Thr) of AGT using allele-specific PCR and allele-induced restriction site PCR. The allele distributions of the microsatellite and the variant T235 of AGT were significantly different between the two ethnic groups. However, no significant allele associations were found with disease when comparing PE/E patients and controls in Australian or Chinese populations, which is in contrast to the two earlier reports. The results suggest that the contribution of AGT to the occurrence of PE/E is small, if anything, and is not constant across populations.

Haplotypes of angiotensinogen in essential hypertension

The M235T polymorphism of the angiotensinogen gene (AGT) has been associated with essential and pregnancy-induced hypertension. Generation of haplotypes can help to resolve whether the T235 allele itself predisposes to the development of hypertension or acts as a marker of an unknown causal molecular variant. We identified 10 diallelic polymorphisms at the AGT locus and genotyped both a series of 477 probands of hypertensive families and 364 controls, all French Caucasians, as well as a series of 92 hypertensives and 122 controls from Japan. Despite a large ethnic difference in gene frequency, a significant association of T235 with hypertension was observed both in Cancasians (.46 vs. .38, P = .004) and in Japanese (.91 vs. .76, P = .002). In both groups, the G-->A substitution located at position -6 upstream of the initial transcription site occurred at the same frequency and in complete linkage disequilibrium with the T235 allele. No other polymorphism was found to be consistently associated with hypertension. Five informative haplotypes subdividing the T235 allele were generated. Whereas two of them were associated with hypertension in Caucasians, none of these two haplotypes (H3 and H4) reached statistical significance in Japanese. The analysis of the AGT-GT repeat revealed marked linkage disequilibriums between each of the diallelic polymorphisms and some (GT)n alleles, with similar patterns in the two populations. The strong disequilibrium between M235 and (GT)16 explained the increased frequency of that particular allele in French controls compared with hypertensives (.42 vs. .36, P < .01). The haplotype combining the M235T and G-6A polymorphisms appears as the ancestral allele of the human AGT gene and as the one associated with hypertension.