Genetics of Human Primary Hypertension: Focus on Hormonal Mechanisms

Increasingly, primary hypertension is being considered a syndrome and not a disease, with the individual causes (diseases) having a common sign-an elevated blood pressure. To determine these causes, genetic tools are increasingly employed. This review identified 62 proposed genes. However, only 21 of them met our inclusion criteria: (i) primary hypertension, (ii) two or more supporting cohorts from different publications or within a single publication or one supporting cohort with a confirmatory genetically modified animal study, and (iii) 600 or more subjects in the primary cohort; when including our exclusion criteria: (i) meta-analyses or reviews, (ii) secondary and monogenic hypertension, (iii) only hypertensive complications, (iv) genes related to blood pressure but not hypertension per se, (v) nonsupporting studies more common than supporting ones, and (vi) studies that did not perform a Bonferroni or similar multiassessment correction. These 21 genes were organized in a four-tiered structure: distant phenotype (hypertension); intermediate phenotype [salt-sensitive (18) or salt-resistant (0)]; subintermediate phenotypes under salt-sensitive hypertension [normal renin (4), low renin (8), and unclassified renin (6)]; and proximate phenotypes (specific genetically driven hypertensive subgroup). Many proximate hypertensive phenotypes had a substantial endocrine component. In conclusion, primary hypertension is a syndrome; many proposed genes are likely to be false positives; and deep phenotyping will be required to determine the utility of genetics in the treatment of hypertension. However, to date, the positive genes are associated with nearly 50% of primary hypertensives, suggesting that in the near term precise, mechanistically driven treatment and prevention strategies for the specific primary hypertension subgroups are feasible.

Insertion/deletion polymorphism of the angiotensin-converting enzyme gene and the risk of hypertension among residents of two cities, South-South Nigeria

BACKGROUND

Hypertension is a public health challenge due to its high prevalence, and is a major risk factor for cardiovascular diseases. This study was designed to determine the frequency of the I/D polymorphism of the angiotensin-converting enzyme gene and its association with hypertension in a sample population of Calabar and Uyo, South-South Nigeria.

MATERIALS AND METHODS

A population-based case control design consisting of total of 1224 participants, 612 each of patients and controls, were randomly recruited from hypertension clinics and the general population. The I/D polymorphism was investigated using polymerase chain reaction. Multiple regression and odds ratio (OR) was applied to test whether the ID genotypes were predictors of hypertension.

RESULTS

The I/D genotype frequencies were 73(12%), 262(43%) and 277(45%); 74(12%), 303(50%) and 235(38%) for the II, ID, DD genotype in patient and control groups, respectively. A higher frequency of the ID genotype was observed in controls of which 208(61%) were females. By multiple regression analysis, age was a predictor for SBP in patients, r = 0.596, and DBP in controls, r = 0.555. Gender, Body mass index, I/D genotypes were not significant predictors for hypertension but the I/D polymorpism was associated with an increased risk for hypertension with an OR of 1.15 95%CI (0.924-1.456).

CONCLUSION

The I/D polymorphism of the angiotensin-converting enzyme gene was a risk factor for hypertension in the sample population of Calabar and Uyo. This research will form baseline information for subsequent molecular studies in this population.

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.

Association of angiotensin-converting enzyme gene insertion/deletion polymorphism with decreased risk for basal cell carcinoma

The incidence of basal cell carcinoma (BCC) is significantly reduced in individuals treated with inhibitors of angiotensin I-converting enzyme (ACE) that produces angiotensin II. The objective of this study was to investigate the possible association of a functional polymorphism in the ACE gene, which affects its transcription, with risk for BCC. In DNA samples of 92 patients with BCC and 103 healthy controls of Greek origin and comparable age and gender, we studied the ACE gene insertion/deletion (I/D) polymorphism. Fisher's exact test was used for comparison of allele and genotype frequencies between the control and patients' groups. The detected low expression I allele frequency in the group of BCC patients was significantly decreased compared to controls (15.8 vs. 31.1 %, respectively; P = 0.001). ID heterozygotes exhibited 3.06 times lower BCC risk, compared with DD homozygotes (P = 0.001; OR = 0.327, 95 % CI = 0.174-0.615). The protective role of I allele was particularly prominent in women (P = 0.007, OR = 0.299, 95 % CI = 0.125-0.716), while for men it exhibited a marginal level (P = 0.041). These findings indicate that the low expression ACE I allele carriers have a decreased risk for BCC. The protective effect of the ID genotype against BCC may be explained by a possible underlying mechanism involving the effect of produced angiotensin II levels on its receptors due to putatively different binding affinity.

Regular consumption of pulses for 8 weeks reduces metabolic syndrome risk factors in overweight and obese adults

Pulses are low in energy density, supporting their inclusion in the diet for the management of risk factors of the metabolic syndrome (MetSyn). The aim of the present study was to describe the effects of frequent consumption (five cups/week over 8 weeks) of pulses (yellow peas, chickpeas, navy beans and lentils), compared with counselling to reduce energy intake by 2093 kJ/d (500 kcal/d), on risk factors of the MetSyn in two groups (nineteen and twenty-one subjects, respectively) of overweight or obese (mean BMI 32·8 kg/m2) adults. Body weight, waist circumference, blood pressure, fasting blood parameters and 24 h food intakes were measured at weeks 1, 4 and 8. Blood glucose, insulin, C-peptide, glucagon-like peptide-1 (GLP-1) and ghrelin were measured after a 75 g oral glucose load at weeks 1 and 8. At week 8, both groups reported reductions in energy intake, waist circumference, systolic blood pressure, glycosylated Hb (HbA1c) and glucose AUC and homeostasis model of insulin resistance (HOMA-IR) following the glucose load (P < 0·05). However, HDL, fasting C-peptide and insulin AUC responses were dependent on diet (P < 0·05). HDL and C-peptide increased by 4·5 and 12·3 %, respectively, in the pulse group, but decreased by 0·8 and 7·6 %, respectively, in the energy-restricted group. Insulin AUC decreased in both females and males on the energy-restricted diet by 24·2 and 4·8 %, respectively, but on the pulse diet it decreased by 13·9 % in females and increased by 27·3 % in males (P < 0·05). In conclusion, frequent consumption of pulses in an ad libitum diet reduced risk factors of the MetSyn and these effects were equivalent, and in some instances stronger, than counselling for dietary energy reduction.

The association of ACE I/D gene polymorphism with severe carotid atherosclerosis in patients undergoing carotid endarterectomy

Introduction: The ACE I/D polymorphism was mostly investigated in association with intima-media thickness, rarely with severe atherosclerotic phenotype.

Materials and methods: We investigated the association of I/D polymorphism with severe carotid atherosclerosis (CA) (stenosis > 70%) in asymptomatic and symptomatic patients undergoing carotid endarterectomy. The 504 patients subjected to endarterectomy and 492 healthy controls from a population in Serbia were investigated as a case-control study.

Results: The univariate logistic regression analysis revealed ACE DD as a significant risk factor for severe CA (odds ratio [OR] = 1.3, 95% confidence interval [CI] 1.0–1.7, p = 0.04). After adjustment for the common risk factors (age, hypertension, smoking, and HDL) ACE was no longer significant. However, we found a significant independent influence of DD genotype on plaque presence in a normotensive subgroup of patients (OR 1.8, CI 1.2–3.0, p = 0.01, corrected for multiple testing). In symptomatic patients D allele carriers were significantly more frequent compared with asymptomatic patients (OR 1.6 CI 1.0–2.6, p = 0.05).

Conclusions: Our data suggests that ACE I/D is not an independent risk factor for severe CA. On the other hand, a significant independent genetic influence of ACE I/D appeared in normotensive and symptomatic patients with severe CA. This should be considered in further research toward resolving the complex genetic background of severe CA phenotype.

Polymorphisms of renin-angiotensin system and natriuretic peptide receptor A genes in patients of Greek origin with a history of myocardial infarction

We assessed the association between (CA)n repeat polymorphism of angiotensinogen (AGT), 250 base pair (bp) insertion/deletion (I/D) of angiotensin-converting enzyme (ACE), tetranucleotide repeat polymorphism (TCTG)n of renin (REN), (CT)n repeat polymorphism of the natriuretic peptide receptor A (NPRA) genes, and the presence and extent of coronary artery disease (CAD) in Greek patients with a history of myocardial infarction (MI). A total of 158 post-MI patients referred for coronary angiography were compared with 144 controls. The SS genotype of the AGT gene was related with an increased risk for 3-vessel CAD (odds ratio [OR], 1.94; 95% confidence interval [CI], 1.05-3.61; P = .041), whereas the SL genotype was related with a decreased risk (OR, 0.44; 95% CI, 0.22-0.87; P = .019). Moreover, there was a trend for the SL genotype of the REN gene toward increased risk for CAD. There was a significant association between (CA)n polymorphism of the AGT gene and the extent of CAD in Greek patients with a history of MI.

Renin-angiotensin-aldosterone system gene polymorphisms in coronary artery bypass graft surgery patients

INTRODUCTION

Candidates for coronary artery bypass grafting (CABG) represent a group of patients with well documented, severe coronary artery disease (CAD). Genetic polymorphisms of renin-angiotensin-aldosterone system (RAAS) components have been associated with CAD. We examined the association of polymorphisms of angiotensin-converting enzyme (ACE), angiotensinogen (AGT), and angiotensin II type 1 receptor (AT(1) receptor) with severe CAD in CABG patients.

MATERIALS AND METHODS

One hundred and fifty-four CABG patients and 155 non-CAD controls were included in the study. Established PCR methods were used for genotyping of AGT M235T, AGT T174M, AT(1) receptor A1166C, and ACE I/D polymorphisms. Cumulative effect of analysed polymorphisms was assessed by calculation of each individual's RAAS gene score (addition of 0.5 points for each variant allele and then calculating the sum for all four polymorphisms).

RESULTS

No association between AGT M235T, AGT T174M, ACE I/D and AT(1) receptor A1166C polymorphisms and CAD was observed. Within CABG patients, the frequency of homozygous AGT 235TT genotype was higher in hypertensive compared to normotensive CABG patients (21.7% vs. 6.3%, p=0.03). RAAS gene score did not differ between CABG patients and non-CAD controls.

CONCLUSIONS

There is no association of the analysed RAAS polymorphisms with severe CAD in CABG patients. However, within these patients, an association was found between AGT 235TT genotype and hypertension.