Recent studies suggest that the ANP (atrial natriuretic peptide)/NPRA (type A natriuretic peptide receptor) system modulates ventricular remodelling and cardiac hypertrophy in hypertension in Western populations. In the present study, we tested for any association between two SNPs (single nucleotide polymorphisms) in the ANP gene (one in the promoter and one exonic) with cardiac hypertrophy. We tested the hypothesis in 2118 hypertensive patients, including 945 with LVH [LV (left ventricular) hypertrophy] and 1173 without LVH, as well as 816 healthy control subjects. All subjects were genotyped for the −A2843G and A188G polymorphisms. We found that the GG genotype at position −2843 conferred a 2.2-fold risk for LVH compared with the AA or AG genotypes, including septal wall thickness (11.8±1.4 mm for GG compared with 10.9±1.4 and 10.7±1.3 mm for AA and AG respectively; P<0.01), posterior wall thickness (11.8±2.8 mm for GG compared with 10.6±1.2 and 10.6±1.4 mm for AA and AG respectively; P<0.01), LV mass index (62.7±13.6 g/m2.7 for GG compared with 57.9±8.6 and 57.8±8.4 g/m2.7 for AA and AG respectively; P<0.05) and relative wall thickness (50.7±10.8% for GG compared with 44.3±7.3 and 43.5±6.8% for AA and AG respectively; P<0.05). Plasma levels of ANP were significantly lower in the hypertensive patients with LVH carrying the GG genotypes compared with those carrying the AA or AG genotypes (P<0.01). No association of GG genotype with echocardiographic variables and plasma ANP levels was identified in hypertensive patients without LVH and in control subjects (P>0.05). No significant association between the A188G genotype and echocardiographic variables was found in either hypertensive patients or controls (P>0.05). In conclusion, our findings indicate that the −A2843G polymorphism in the ANP gene promoter might be a genetic risk factor for the development of LVH in patients with hypertension.

INTRODUCTION

LVH [LV (left ventricular) hypertrophy] is associated with cardiovascular morbidity and mortality, as well as all-cause mortality [1,2]. LVH is also independently associated with the risk of ischaemic stroke [3]. Although hypertension is a major cause of LVH, the degree of LVH is not in parallel with the level of BP (blood pressure), the duration of hypertension or reversal of hypertensive LVH by pharmacological treatment. This implies that other factors may be involved in LVH in addition to BP. It has been reported that genetic factors account for approx. 60% of the BP-independent variance of cardiac mass [4].

ANP (atrial natriuretic peptide) is an endogenous vasoactive peptide, and maintains the homoeostasis of circulatory blood volume and sodium homoeostasis by inducing diuresis and natriuresis, and vasodilator effect [5]. Cardiac hypertrophy results in reactivation of fetal gene expression in cardiac myocytes, which is accompanied by a significant induction of ANP gene promoter activity [6]. Cohort studies have proved that plasma ANP levels are increased in EH (essential hypertension) patients with LVH [7,8]. ANP might play a role in protecting the heart from hypertrophic stimuli, suggesting that up-regulation of ANP is a protective and compensatory response to hypertrophic stimuli in the development of LVH [9].

A recent study found that the −C664G promoter polymorphism in the gene encoding ANP is responsible for the down-regulation of ANP gene transcription, and is associated with LVH in Italians [10]; however, this association has not been tested in other ethnic groups. Because the SNP (single nucleotide polymorphism) −C664G is monomorphic in Chinese populations and no other SNPs are in LD (linkage disequilibrium) with the −C664G promoter polymorphism, we investigated whether the two polymorphisms in the promoter and exon 1 regions of the ANP gene were associated with LVH in 2118 hypertensive patients without or with LVH compared with 816 healthy control subjects.

MATERIALS AND METHODS

Subjects

Subjects were recruited from 24 out of a total of 60 communities in Xinyang, Henan Province, People's Republic of China. The study was started in April 2005. The subjects consisted of 945 hypertensive patients with LVH and 1173 patients without LVH (see Table 1). Hypertension was defined according to WHO (World Health Organization) criteria [11], as SBP (systolic BP) ≥140 mmHg and/or DBP (diastolic BP) ≥90 mmHg on average of two measurements or by current antihypertensive treatment. BPs were measured by the same investigator on the right arm using a mercury sphygmomanometer with standardized techniques after at least 5 min rest in a sitting position. Exclusion criteria included secondary arterial hypertension, atrio–ventricular conduction block, chronic obstructive bronchitis, bronchial asthma, chronic myeloproliferative diseases, diabetes, hypertrophic cardiomyopathy, valvular heart diseases, pulmonary hypertension, coronary heart disease and heart failure. Controls (n=816) were recruited from age- and sex-matched healthy subjects in the same community, who had no history or symptoms of cardiovascular diseases.

Table 1
Clinical characteristics in controls and hypertensive patients

Values are means±S.D. or numbers (%). *P<0.05 and **P<0.01 compared with controls.

Hypertensive patients
CharacteristicControlsWithout LVHWith LVH
n 816 1173 945 
Age (years) 54.7±9.3 57.2±9.5** 59.5±8.1** 
Male gender (n313 (38.4%) 426 (37.2%) 297 (31.4%)* 
BMI (kg/m223.8±3.33 25.0±3.70* 27.3±4.45** 
SBP (mmHg) 118.4±11.2 160.0±22.2** 164.2±27.0** 
DBP (mmHg) 77.65±7.0 95.4±11.4** 96.4±14.6** 
HDL-C (mmol/l) 1.52±0.29 1.56±0.34 1.51±0.33 
LDL-C (mmol/l) 2.59±0.77 3.12±0.88** 3.15±0.89** 
Total cholesterol (mmol/l) 4.99±1.07 5.55±1.12** 5.49±1.11** 
Triacylglycerol (mmol/l) 1.43±0.82 1.78±1.41* 1.77±1.36* 
Glucose (mmol/l) 4.84±1.63 5.78±2.03* 5.54±1.61* 
Cigarette smokers (n196 (24.0%) 230 (19.6%) 149 (15.8%) 
Alcohol consumers (n194 (23.8%) 256 (21.8%) 176 (18.6%) 
Hypertensive patients
CharacteristicControlsWithout LVHWith LVH
n 816 1173 945 
Age (years) 54.7±9.3 57.2±9.5** 59.5±8.1** 
Male gender (n313 (38.4%) 426 (37.2%) 297 (31.4%)* 
BMI (kg/m223.8±3.33 25.0±3.70* 27.3±4.45** 
SBP (mmHg) 118.4±11.2 160.0±22.2** 164.2±27.0** 
DBP (mmHg) 77.65±7.0 95.4±11.4** 96.4±14.6** 
HDL-C (mmol/l) 1.52±0.29 1.56±0.34 1.51±0.33 
LDL-C (mmol/l) 2.59±0.77 3.12±0.88** 3.15±0.89** 
Total cholesterol (mmol/l) 4.99±1.07 5.55±1.12** 5.49±1.11** 
Triacylglycerol (mmol/l) 1.43±0.82 1.78±1.41* 1.77±1.36* 
Glucose (mmol/l) 4.84±1.63 5.78±2.03* 5.54±1.61* 
Cigarette smokers (n196 (24.0%) 230 (19.6%) 149 (15.8%) 
Alcohol consumers (n194 (23.8%) 256 (21.8%) 176 (18.6%) 

The study protocol was approved by the Institutional Review Boards of the participating hospitals and by the Beijing Municipal Commission of Science and Technology. Informed consent was obtained from all individuals. All investigators were qualified to undertake the study.

Determination of biochemical variables and clinical data collection

Blood samples were collected after a 12 h overnight fast. All samples were analysed using an automatic analyser (Hitachi 7060, Hitachi) for serum sodium, potassium, creatinine, uric acid, blood urea nitrogen, total plasma cholesterol, triacylglycerol (triglyceride), HDL-C (high-density lipoprotein cholesterol), LDL-C (low-density lipoprotein cholesterol) and blood glucose within 3 months. In addition, a complete medical history was obtained from all subjects, including family history of hypertension and diabetes mellitus, and the following cardiovascular risk factors: alcohol intake, cigarette smoking, family history of coronary heart disease or stroke, weight, height, BMI (body mass index), SBP and DBP. BMI was calculated by using the formula of weight (kg)/height (m2). Creatinine clearance rate was calculated by using the formula: [140−age (years)]×weight (kg)/[72×serum creatinine (mg/dl)] for males, and [140−age (years)]×weight (kg)/[72×serum creatinine (mg/dl)]×0.85 for females [12].

Echocardiography

Echocardiography was performed in all hypertensive patients and control subjects using either an HP 5500 (Phillips Medical System) or an HDI 3000 (ATL) machine. The transducer frequency was 2.5–3.5 MHz. M-mode and real-time two-dimensional images were recorded at 30 frames/s on super TDK videotape. Subjects were examined in the supine and left lateral position by three experienced investigators, who were blinded to the patient's genotype. Echocardiographic images were obtained in the parasternal long- and short-axis views, and apical two- and four-chamber views with standard transducer positions [13]. Three physician-echocardiographers supervised the echocardiographic examination.

LV internal diameters, septal thickness and posterior wall thickness were measured in up to three cardiac cycles at end-diastole and end-systole, according to the recommendations of the American Society of Echocardiography [14].

LVM (LV mass) was calculated at end-diastole using the formula: 0.8×1.04[(IVSd+LVIDD+PWTd)3−LVIDD3]+0.6 (where IVSd is interventricular septal thickness, PWTd is posterior wall thickness, and LVIDD is LV end-diastolic internal dimension), which yields values closely related (R=0.90) to necropsy LV weight [15]. LVM was divided by height2.7 to obtain LVMI (LVM index). LVH was defined as LVMI >49.2 g/m2.7 for men and >46.7 g/m2.7 for women [16]. RWT (relative wall thickness) was calculated using the formula: (IVSd+PWTd)/LVEDD [17], where LVEDD is LV end-diastolic diameter.

SNP selection of the ANP gene

According to the SNP database of NCBI (National Center for Biotechnology Information) and HapMap, only two SNPs, −A2843G and A188G (resulting in a Met>Val transposition), met the criteria of MAF (minor allele frequency) >5% within the promoter and coding region of the ANP gene in Chinese populations. Therefore these two polymorphisms were selected to investigate whether they were associated with LVH in patients with hypertension.

Genotyping

Peripheral blood (10 ml) was collected into tubes containing trisodium citrate (final concentration in blood, 0.026 mol/l), and centrifuged at 3000 g for 10 min at room temperature (25 °C). Plasma and ‘buffy coats’ were separated and stored in 1.5 ml tubes at −70 °C. All assays were performed in duplicate. DNA was extracted from ‘buffy coats’ as described previously [18] and stored at −70 °C before use.

The −A2843G and A188G polymorphisms of the ANP gene were determined by PCR/RFLP (restriction-fragment-length polymorphism). The sequence containing the −A2843G polymorphism was amplified by PCR with the following primers: 5′-TAGGGATGATCGTTGCTGACTTTG-3′ and 5′-GAGTGACCTTTTGCCTTGGGATT-3′. The resulting 125 bp fragment was digested with Hinf1 (New England Biolabs). Two fragments of 103 and 22 bp were observed for the G allele on a 4% (w/v) agarose gel, whereas only the 125 bp band was seen for the A allele. The sequence containing the A188G polymorphism in exon 1 was amplified by PCR, with the sense primer 5′-GCAGTGGATTGCTCCTTGACGAC-3′ and antisense primer 5′-ATCCATCAGGTCTGCGTTGGACT-3′. The resultant PCR products of 146 bp were digested with Hinf1 (New England Biolabs). Two fragments of 124 bp and 22 bp were observed for the G allele on a 4% (w/v) agarose gel, whereas only the 146 bp band was seen for the A allele. The detected variation was confirmed by sequencing 500 random samples with an ABI Prism 3730 Genetic Analyser (PE Applied Biosystems) [19], and the reproducibility was 100%.

Determination of plasma ANP levels

To investigate further the impact of gene polymorphisms on pathological phenotypes, the levels of plasma ANP were determined in hypertensive patients without or with LVH and in control subjects, and were analysed according to the −A2843G different genotypes. For the determination of plasma ANP levels, 13 GG homozygotes, 18 heterozygotes and 19 homozygotes were selected from hypertensive patients with LVH, five GG homozygotes, 19 AG heterozygotes and 20 AA homozygotes were selected from hypertensive patients without LVH, and seven GG homozygotes, 18 AG heterozygotes and 17 AA homozygotes were selected from the control subjects. Blood samples for the determination of ANP were collected on ice in tubes containing EDTA and aprotinin and were centrifuged at 3000 g for 15 min at 4 °C to isolate plasma. Plasma samples were then frozen at −70 °C. The plasma ANP assay was performed within 3 months using a commercial RIA kit (Eastern Asia Radioimmunity Research Institute), according to the manufacturer's instructions.

Statistical analysis

Results are expressed as means±S.D. A χ2 test was used in testing categorical variables, the Hardy–Weinberg equilibrium of the polymorphisms and genotype/allele frequencies. One-way ANOVA was used for comparison of quantitative variables. A general linear univariate model was performed, considering each cardiac echocardiographic parameter as a dependent variable, and covariates including age, gender, BMI, SBP, DBP, glucose, creatinine clearance rate, HDL-C, LDL-C, triacylglycerol, total plasma cholesterol, and independent variables including the −A2843G and A188G polymorphisms. A Bonferroni test was used for adjustment for multiple comparison. Association of the −A2843G polymorphism with LVH was analysed by multivariate logistic regression adjusted by age, gender, BMI, SBP, DBP, smoking, alcohol consumption, glucose, HDL-C, LDL-C, total plasma cholesterol and triacylglycerol in hypertensive patients. Statistical analysis was performed with the SPSS 13.0 package. A value of P<0.05 was considered significant. r2 was used to determine LD with the software EMLD (http://202.120.7.14/analysis/myAnalysis.php). D′ and r2 were used to indicate the strength of LD.

RESULTS

Characteristics of the study subjects

Clinical characteristics of the subjects are shown in Table 1. SBP, DBP and BMI, and levels of triacyglycerol, total plasma cholesterol, glucose and LDL-C, were significantly higher in hypertensive patients without or with LVH compared with controls.

Association of genotype with phenotype

The distributions of the GG, AG and AA genotypes of the −A2843G polymorphism are shown in Table 2. Distributions were in agreement with the Hardy–Weinberg equilibrium in both patients and controls. The frequency of the GG genotype was higher in hypertensive patients with LVH compared with either hypertensive patients without LVH or controls (P=0.03 and P=0.02 respectively), whereas no difference was identified in the frequency of the GG genotype between hypertensive patients without LVH and controls.

Table 2
Distribution of the −A2843G and A188G genotypes in controls and hypertensive patients

*P<0.05 compared with hypertensive patients without LVH or controls, as determined using a χ2 test.

−A2843G genotype (n)A188G genotype (n)
PopulationGGAGAAGGAGAA
Controls (n=816) 7 (0.9%) 169 (20.7%) 640 (78.4%) 7 (0.9%) 132 (16.2%) 677 (83.0%) 
Hypertensive patients (n=2118) 30 (1.4%) 418 (19.7%) 1670 (78.8%) 11 (0.5%) 406 (19.2%) 1701 (80.3%) 
Hypertensive patients       
 With LVH (n=945) 20 (2.1%)* 194 (20.5%) 731 (77.4%) 6 (0.6%) 197 (20.8%) 742 (78.5%) 
 Without LVH (n=1173) 10 (0.9%) 224 (19.1%) 939 (80.1%) 5 (0.4%) 209 (17.8%) 959 (81.8%) 
−A2843G genotype (n)A188G genotype (n)
PopulationGGAGAAGGAGAA
Controls (n=816) 7 (0.9%) 169 (20.7%) 640 (78.4%) 7 (0.9%) 132 (16.2%) 677 (83.0%) 
Hypertensive patients (n=2118) 30 (1.4%) 418 (19.7%) 1670 (78.8%) 11 (0.5%) 406 (19.2%) 1701 (80.3%) 
Hypertensive patients       
 With LVH (n=945) 20 (2.1%)* 194 (20.5%) 731 (77.4%) 6 (0.6%) 197 (20.8%) 742 (78.5%) 
 Without LVH (n=1173) 10 (0.9%) 224 (19.1%) 939 (80.1%) 5 (0.4%) 209 (17.8%) 959 (81.8%) 

The association between echocardiographic variables and the −A2843G polymorphism was tested by the general linear univariate model and showed that GG homozygote patients with LVH had a significant increase in IVSd, PWTd, LVMI and RWT compared with either AA homozygote or AG heterozygote patients with LVH (Table 3). However, no significant differences were seen in EDDs (P>0.05) and ESDs (end-systolic diameters) (P>0.05) among the patients carrying the different genotypes (Table 3). The GG homozygous genotype conferred a 2.2-fold increase in risk of LVH in hypertensive patients with LVH after adjustment for conventional cardiovascular risk factors (Table 4). These associations were not found in hypertensive patients without LVH (Tables 3 and 4) or in controls (Table 3).

Table 3
Echocardiographic variables in controls and hypertensive patients according to the ANP −A2843G genotype

Results are means±S.D. A general linear univariate model was performed, considering each cardiac echocardiographic variable as a dependent variable, with covariates including age, gender, BMI, SBP, DBP, glucose, HDL-C, LDL-C, triacylglycerol and total plasma cholesterol. A Bonferroni test was performed for adjustment of multiple comparisons. The difference was significant at P<0.05. *P<0.05 and **P<0.01 compared with GG.

Controls (n=816)Hypertensive patients with LVH (n=945)Hypertensive patients without LVH (n=1173)
Variable−A2843G genotype…GGAGAAGGAGAAGGAGAA
n  169 640 20 194 731 10 224 939 
IVSd (mm)  8.7±1.2 8.5±1.0 8.4±1.2 11.8±1.4 10.7±1.3** 10.9±1.4** 8.9±0.9 9.2±1.3 9.3±1.3 
LVPW (mm)  8.7±1.3 8.5±1.0 8.5±1.1 11.8±2.8 10.6±1.4** 10.6±1.2** 8.9±0.9 9.0±1.1 9.1±1.0 
EDD (mm)  45.2±2.9 43.2±4.6 43.9±4.1 47.2±4.6 48.5±4.3 49.1±4.6 44.7±3.9 44.8±4.4 44.0±4.5 
ESD (mm)  31.2±2.5 27.0±3.6 28.0±4.1 31.3±6.5 33.1±5.3 32.5±5.2 28.3±4.6 28.7±4.8 28.6±4.6 
RWT (%)  37.1±4.2 39.9±5.9 39.0±5.7 50.7±10.8 43.5±6.8* 44.3±7.3* 39.9±3.1 42.2±7.1 42.4±7.2 
LVMI (g/m2.7 34.2±5.6 34.2±6.6 34.2±6.4 62.7±13.6 57.8±8.4* 57.9±8.6* 37.7±6.2 38.4±5.9 37.8±6.2 
Controls (n=816)Hypertensive patients with LVH (n=945)Hypertensive patients without LVH (n=1173)
Variable−A2843G genotype…GGAGAAGGAGAAGGAGAA
n  169 640 20 194 731 10 224 939 
IVSd (mm)  8.7±1.2 8.5±1.0 8.4±1.2 11.8±1.4 10.7±1.3** 10.9±1.4** 8.9±0.9 9.2±1.3 9.3±1.3 
LVPW (mm)  8.7±1.3 8.5±1.0 8.5±1.1 11.8±2.8 10.6±1.4** 10.6±1.2** 8.9±0.9 9.0±1.1 9.1±1.0 
EDD (mm)  45.2±2.9 43.2±4.6 43.9±4.1 47.2±4.6 48.5±4.3 49.1±4.6 44.7±3.9 44.8±4.4 44.0±4.5 
ESD (mm)  31.2±2.5 27.0±3.6 28.0±4.1 31.3±6.5 33.1±5.3 32.5±5.2 28.3±4.6 28.7±4.8 28.6±4.6 
RWT (%)  37.1±4.2 39.9±5.9 39.0±5.7 50.7±10.8 43.5±6.8* 44.3±7.3* 39.9±3.1 42.2±7.1 42.4±7.2 
LVMI (g/m2.7 34.2±5.6 34.2±6.6 34.2±6.4 62.7±13.6 57.8±8.4* 57.9±8.6* 37.7±6.2 38.4±5.9 37.8±6.2 
Table 4
Association of the ANP −A2843G genotype with LVH in hypertensive patients

ORs (odds ratios) and 95% CIs (confidence intervals) were calculated using multivariate logistic regression analyses. Adjusted ORs were stratified by age, gender, BMI, SBP, DBP, glucose, HDL-C, LDL-C, triacylglycerol and total plasma cholesterol. *P<0.05.

Genotype (n)GG genotype
PopulationGGAGAACrude OR (95% CI)Adjusted OR (95% CI)
Hypertensive patients      
 Without LVH (n=1176) 10 (0.9%) 224 (19.1%) 939 (80.1%) 
 With LVH (n=945) 20 (2.1%) 194 (20.5%) 731 (77.4%) 2.56 (1.19–5.52)* 2.22 (1.01–4.91)* 
Genotype (n)GG genotype
PopulationGGAGAACrude OR (95% CI)Adjusted OR (95% CI)
Hypertensive patients      
 Without LVH (n=1176) 10 (0.9%) 224 (19.1%) 939 (80.1%) 
 With LVH (n=945) 20 (2.1%) 194 (20.5%) 731 (77.4%) 2.56 (1.19–5.52)* 2.22 (1.01–4.91)* 

Plasma ANP levels were measured in 94 hypertensive patients (44 without or 50 with LVH) and in 42 controls. As shown in Table 5, plasma ANP levels were lower in GG homozygote patients compared with AA homozygote (P<0.01) and AG heterozygote (P<0.01) hypertensive patients with LVH. Similar observations were not seen in hypertensive patients without LVH or controls (Table 5).

Table 5
Plasma ANP levels in controls and hypertensive patients according to the −A2843G genotype

Results are means±S.D. One-way ANOVA was performed. **P<0.01 compared with GG; †P<0.05 and ††P<0.01 compared with control subjects

Plasma ANP levels (pg/ml)
Group−A2843G genotype…GGAGAA
Controls (n=42)  125.9±6.0 (n=7) 128.7±13.2 (n=18) 125.6±12 (n=17) 
Hypertensive patients     
 Without LVH (n=44)  135.8±7.4 (n=5)† 140.4±14.4 (n=19)† 142.8±16.0 (n=20)†† 
 With LVH (n=50  96.0±6.0 (n=13)† 143.7±15.1 (n=18)**†† 147.4±13.0 (n=19)**†† 
Plasma ANP levels (pg/ml)
Group−A2843G genotype…GGAGAA
Controls (n=42)  125.9±6.0 (n=7) 128.7±13.2 (n=18) 125.6±12 (n=17) 
Hypertensive patients     
 Without LVH (n=44)  135.8±7.4 (n=5)† 140.4±14.4 (n=19)† 142.8±16.0 (n=20)†† 
 With LVH (n=50  96.0±6.0 (n=13)† 143.7±15.1 (n=18)**†† 147.4±13.0 (n=19)**†† 

The distributions of the GG, AG and AA genotypes of the A188G polymorphism are summarized in Table 2. The distributions were in agreement with the Hardy–Weinberg equilibrium in both patients and controls. No significant differences were found using a χ2 test among the three groups (P=0.09) or in any of the echocardiographic variables.

LD analysis

LD was performed between the −A2843G and A188G polymorphisms by using the standard definition of D′ and r2. We found that the two SNPs were not in LD, with D′=0.35 and r2=0.06, indicating that the two SNPs were not in a same natural haplotype block.

DISCUSSION

In the present study, we have found that the −A2843G promoter polymorphism of the ANP gene is associated with LVH in patients with hypertension. The GG homozygous genotype confers a 2.2-fold increased risk of LVH, independent of conventional cardiovascular risk factors. To our knowledge, the present study is the first investigation to test the association of the variation −A2843G with LVH in large-scale community-based cohorts.

The candidate genes related to EH and LVH have been studied widely. It has been demonstrated that some gene polymorphisms, such as the ACE (angiotensin-converting enzyme) gene G2350A synonymous-coding polymorphism, CYP11B2 (aldosterone synthase) gene −C344T polymorphism and the BDKRB2 (bradykinin B2 receptor gene) promoter −T58C polymorphism, have all been reported to be associated with LVH in hypertensive patients [2022], although conflicting results have been reported. To date, three polymorphisms (−C664G, G1837A and T2238C) of the ANP gene have been investigated in association studies [10,23,24], but these polymorphisms were found to be monomorphic in Chinese populations, and no other SNPs are in LD with −C664G in this region. Therefore two SNPs of the ANP gene were selected to examine the association between the polymorphisms and LVH in patients with hypertension. Our present results are consistent with those reported by Rubattu et al. [10] in an Italian population.

Our present results have shown that the −A2843G promoter polymorphism was associated with LVH in hypertensive patients. In hypertensive patients with LVH, the ventricular wall was thicker in GG homozygotes than in AA homozygotes or AG heterozygotes. No significant associations were found between genotypes and ventricular wall thickness in hypertensive patients without LVH or controls, indicating that GG carriers are susceptible to LVH when having hypertension.

We also found that lower levels of plasma ANP were associated with the promoter allelic variant in hypertensive patients with LVH, but not in hypertensive patients without LVH and controls, supporting the hypothesis that the promoter polymorphism of ANP may be associated with pathological phenotypes. Our present findings are consistent with the results of a previous study in dominant-negative NPRA (type A natriuretic peptide receptor) mice, demonstrating that the cardiac phenotype was normal except when mice were subjected to pressure overload [25]. These results imply that the −G2238G allelic variant associated with a decrease in the plasma ANP contributes to LVH in the presence of hypertension. A previous study [10] suggested that the ANP −664G promoter variant is associated with increased cardiac wall thicknesses and significantly lower plasma ANP levels in hypertensive patients with LVH, supporting the hypothesis that this promoter mutation is involved in the development of LVH in hypertension. Therefore the −G2843G promoter mutation might be involved in the process of LVH via down-regulating ANP levels; however, the precise mechanism remains unknown. Further studies are required to ascertain whether specific transcription factors are involved in different transcriptional activation of the −A2843G variant. In addition, the present study cannot exclude the possibility that other functional SNPs in LD with the −A2843G led to LVH.

The strength of our present study is the large sample size from multiple communities and the different patient population (Chinese in our present study and Italians in the previous study [10]). Furthermore, we used echocardiography instead of electrocardiography to determine LVH. Digital and automated echocardiographic interpretation has a rigorous quality control protocol for the estimation of LVM and has the advantage of unbiased classification of LVH, allowing screening in large populations such as ours [26].

However, some limitations must be considered. Our study population comprised almost twice as many women as men. In addition, different geographical and racial backgrounds of the individuals can affect the consequences of an association study [27]. Therefore our results need to be confirmed in other community-based cohorts.

In conclusion, the −A2843G polymorphism of the ANP gene may be a genetic risk factor for the development of LVH in hypertension. Clarifying the mechanisms underlying the effect of this polymorphisms may help provide a theoretical basis for preventing and individualizing treatment of LVH in hypertensive patients.

Abbreviations

     
  • ANP

    atrial natriuretic peptide

  •  
  • BMI

    body mass index

  •  
  • BP

    blood pressure

  •  
  • DBP

    diastolic BP

  •  
  • EDD

    end-diastolic diameter

  •  
  • EH

    essential hypertension

  •  
  • ESD

    end-systolic diameter

  •  
  • HDL-C

    high-density lipoprotein cholesterol

  •  
  • IVSd

    interventricular septal thickness

  •  
  • LD

    linkage disequilibrium

  •  
  • LDL-C

    low-density lipoprotein cholesterol

  •  
  • LV

    left ventricular

  •  
  • LVH

    LV hypertrophy

  •  
  • LVM

    LV mass

  •  
  • LVMI

    LVM index

  •  
  • PWTd

    posterior wall thickness

  •  
  • RWT

    relative wall thickness

  •  
  • SBP

    systolic BP

  •  
  • SNP

    single nucleotide polymorphism

The study was supported by Ministry of Science & Technology of China with grant (2006CB503805) to H.R.

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