Association between the A46G polymorphism (rs1042713) in the β2-adrenergic receptor gene and essential hypertension susceptibility in the Chinese population

Supplemental Digital Content is available in the text


Introduction
Hypertension, 1 of the most prevalent chronic diseases globally, is a risk factor for most cardiovascular and cerebrovascular diseases. [1][2][3] With the urbanization and economic growth of China, the hypertension prevalence in China is increasing. [4] According to a nationally representative cross-sectional study published in 2018, 23.2% of Chinese adults aged ≥18 years had essential hypertension. [5] Essential hypertension is considered to be a complex disorder resulting from the interaction of genetic and environmental factors. [6] Although environmental factors, such as obesity, alcohol drinking, and sodium intake, act as risk factors for hypertension, the contribution of genetic factors to essential hypertension cannot be neglected. [6,7] With the development of sequencing technology, more and more variants in specific genes have been found to be associated with essential hypertension. [8,9] b2-adrenergic receptor (ADRB2), a G-protein-coupled receptor, is regarded to be involved in the regulation of blood pressure in humans. [10] ADRB2 plays a potential role in blood pressure regulating by their action on vascular resistance, renin release, and renal sodium excretion. [11][12][13] Several genetic polymorphisms have been identified in ADRB2, of which the A46G (rs1042713, Arg16Gly) variant is the most frequent. [14] The Arg16→Gly substitution has been shown to enhance the agonist-mediated receptor downregulation. [15] There have been many studies conducted to investigate the association between the ADRB2 A46G polymorphism and the risk of hypertension in the Chinese population. [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] However, the results of previous studies were conflicting. Therefore, we performed the present systematic review and meta-analysis to further investigate the association between the ADRB2 A46G polymorphism and essential hypertension risk in the Chinese population.

Search strategy
We performed a systematic search to identify all relevant studies on PubMed, Embase, Ovid, Web of Science, Chinese National Knowledge Infrastructure, Wan Fang, and China Biology Medicine disc databases up to January 3, 2020. The following subject terms or suitable keywords were used to perform the search: ADRB2 gene, b2-AR, polymorphism, variant, mutation, and hypertension with languages limited to Chinese and English (see Supplemental Digital Content, which illustrates the search strategy on PubMed, http://links.lww. com/MD/F204). In order to include all possible relevant articles, references of relevant review articles and case-control studies were also searched. Two reviewers (Liyuan Yan, MD, and Haipeng Wang, PhD) independently performed the search and downloaded the full text of any possible relevant studies. The ethical approval and consent from patients were not needed because our study was based on previous published case-control studies. The meta-analysis was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses.

Study selection
Studies included in the present meta-analysis must meet the following criteria: (1) studies investigated the relationship between the A46G polymorphism in the ADRB2 gene and essential hypertension; (2) studies with an unrelated case-control design in the Chinese population; (3) studies provided enough data for us to calculate ORs and 95% confidence interval (CIs); (4) studies fit the Hardy-Weinberg equilibrium (HWE) test in controls.
When it comes to duplicate publications, we only included the article with larger sample size and more comprehensive outcome information than the others. Two reviewers (Liyuan Yan, MD, and Haipeng Wang, PhD) independently performed the selection of included articles, and any conflicts between 2 reviewers were judged by a third reviewer (Xin Zhao, PhD).

Data extraction
Two authors (Liyuan Yan, MD, and Haipeng Wang, PhD) independently conducted the extraction of useful data from all studies included in our meta-analysis. The following data were extracted from included articles: name of the first author, year of publication, ethnicities, geographic location, number of cases and controls, mean age of cases and controls, genotypes distribution, source of controls, genotyping methods, and results of the HWE test in controls. Any conflicts between 2 reviewers were discussed with a third reviewer (Xin Zhao, PhD).

Quality assessment
Two reviewers (Liyuan Yan, MD, and Haipeng Wang, PhD) independently evaluated the quality of articles by using the 9point Newcastle-Ottawa Scale (NOS). [32] Each study was evaluated based on 3 aspects, including selection, comparability, and exposure. If the total scores of a study were less than six, it would be excluded from our meta-analysis.

Statistical analyses
All statistical analyses were conducted using Stata version 15.0 (Stata Corporation, College Station, TX). We used the chi-square test to assess the HWE of genotype in controls of each included study. The Q statistic test was performed to assess the interstudy heterogeneity, and P < .10 was considered that there was significant interstudy heterogeneity. The I 2 statistic was calculated to quantify the effect of statistical heterogeneity. The sensitivity test was also used to find the origin of interstudy heterogeneity. The combined OR and 95% CI were calculated to estimate the association between the ADRB2 A46G polymorphism and essential hypertension risk under either a fixed-effect model (Mantel-Haenszel method) or a random-effect model (DerSimonian-Laird method) according to the degree of the between-study heterogeneity. If I 2 < 50%, a fixed-effect model was used. A random-effect model was used to combine the results of included studies when I 2 ≥50%. The analyses were conducted under 5 genetic models: allele genetic model (G versus A), homozygote genetic model (GG versus AA), heterozygote genetic model (AG versus AA), recessive genetic model (GG versus AA +AG), and dominant genetic model (AG+GG versus AA). In order to test the reliability of the pooled results, the sensitivity analyses were performed. We used Egger test and drawn Begg funnel plots to assess the publication bias in our study. P ≥ .05 indicated that there was no significant publication bias in our study.

Characteristics of included studies
The search of the 7 databases identified a total of 420 records. There were 299 records left after removing duplicate records. After screening the titles and abstracts of the 299 left records, 242 articles were excluded because they had nothing to do with the aim of our study. After reading the full text of the left 57 articles, 41 articles were excluded for the following reasons: 2 provided too limited data for us to calculate the pooled ORs and 95% CIs, 16 were not related to the Chinese population, 4 were not in an unrelated case-control design, 14 were duplicate publications, and 5 did not fit the HWE test in controls. Finally, a total of 16 articles (17 studies), containing 3489 cases and 2662 controls, were included in our meta-analysis. The complete selection and exclusion procedure of studies is shown in Figure 1. The characteristics of the included studies are shown in Table 1 Tibetan minority populations, respectively. The NOS scores of included studies are shown in Table 2. All the 17 studies were of six or more NOS scores, which indicated the excellent quality of the included studies. The ADRB2 A46G polymorphism genotype distribution and allele frequency in cases and controls are shown in Table 3.

Results of meta-analysis
Initially, we conducted a combination of the results of all 17 studies. There were no significant associations between the ADRB2 A46G polymorphism and hypertension risk under five genetic models: allele genetic model  Table 4). There was great interstudy heterogeneity in the pooled analyses. Therefore, we conducted sensitivity analyses to discover the origin of the interstudy heterogeneity. As shown in Figure 2, the combined results greatly changed after omitting 1 study about the Chinese Yi minority population. Therefore, we performed pooled analyses without the study related to the Chinese Yi minority population. With this change, we found that there were significant associations between the ADRB2 A46G  Table 4). We also performed subgroup analyses based on the source of controls and ethnicity. The detailed information was shown in Table 4. In subgroup analyses based on the source of controls, significant associations were observed between the ADRB2 A46G polymorphism and hypertension risk in the hospital-based group. Similar associations were also found between the ADRB2 A46G polymorphism and hypertension risk in the Han group, but not in the Chinese minority group.

Sensitivity analyses
The sensitivity analysis was performed to explore whether the combined results would change quantitatively after omitting 1 study at each round of the analysis. As shown in Figure 4, there was no quantitative alternation of the combined results, which indicated the reliability of our results.

Publication bias
The publication bias is an inevitable problem when performing a meta-analysis. We used Egger test and drawn Begg funnel plots. As shown in Figure 5, the distribution of the 16 studies were symmetrically on the 2 sides, which indicated there was no publication bias in our present meta-analysis (Egger test: allele model: P = .89; homozygote model: P = .86; heterozygote model: P = .72; dominant model: P = .86; recessive model: P = .61).

Discussion
Essential hypertension is caused by the interaction of environmental and genetic factors. [6] With the development of sequencing technology, more and more single nucleotide polymorphisms have been found to be related to hypertension susceptibility. [9] The sympathetic nervous system contributes to the regulation of blood pressure by affecting cardiac output, the total peripheral vascular resistance, and sodium handling. [33] The ADRB2 gene, as a pivotal adrenergic pathway gene of the sympathetic nervous system, plays an important role in cardiac output, air smooth muscle tone, and vasodilation. [34] On the term of physiology, variants of the ADRB2 gene may result in Table 1 Characteristics of the studies included for meta-analysis.

Table 2
The results of Newcastle-Ottawa Scale.

Study Selection Comparability Exposure
Wu H (2001) [ Table 4 Meta-analysis of the association between the ADRB2 A46G polymorphism and hypertension risk. hypertension by attenuating vasodilation, which leads to the increase of vascular resistance. [33] The ADRB2 A46G polymorphism, which forms AA, AG, and GG 3 patterns, is 1 of the most studied single nucleotide polymorphisms in the ADRB2 gene. So far, there have been many studies performed to investigate the relationship between the A46G polymorphism in the ADRB2 gene and the risk of essential hypertension in the Chinese population. [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] However, the results Srevious studies were inconsistent. Several case-control studies suggested that the ADRB2 A46G polymorphism increased the risk of hypertension in the Chinese population. However, there was no significant association between the ADRB2 A46G polymorphism and hypertension risk in some other studies. There have been 2 meta-analyses published before exploring the relationship between the ADRB2 A46G polymorphism and essential hypertension susceptibility. [35,36] The first 1 published in 2010 found that the ADRB2 A46G polymorphism was associated with hypertension risk in Mixed Africans. In this meta-analysis, only 2 studies in the Chinese population were included, and no significant association was found between the ADRB2 A46G polymorphism and hypertension risk in Asians. [36] The other meta-analysis published in 2012, which contained 11 studies, indicated that the ADRB2 A46G polymorphism increased the risk of hypertension in the Han Chinese population under the homozygote and recessive model. [35] There have been several studies published since 2012, and several studies conducted in the Chinese minority population were not included in previous metaanalyses. [21,26,[29][30][31] Therefore, we conducted the present metaanalysis to further investigate the association between the ADRB2 A46G polymorphism and the risk of essential hypertension in the Chinese population.
In pooled analyses of all 17 studies, there was no significant association between the ADRB2 A46G polymorphism and hypertension risk under five genetic models. However, we observed great heterogeneity among the included studies. One study [21] related to the Yi minority population was found to result in great interstudy heterogeneity by using the sensitivity analysis. It may suggest that the ADRB2 A46G polymorphism plays a different role in hypertension risk in the Yi minority population, and more studies concerning the Yi minority are needed. After removing the above study, we conducted the metaanalysis of 5 ethnic groups (Han, Hani, Kazak, Uyghur, and Tibetan Chinese population), containing 3390 cases and 2528 controls. Moreover, we found that the ADRB2 A46G was correlated to the increased risk of essential hypertension risk under the allele, homozygous, dominant, and recessive genetic model. There was no significant interstudy heterogeneity under the homozygote genetic model and the recessive genetic model. No publication bias was observed in our study. Sensitivity analyses showed the reliability of our pooled results of 16 studies. In subgroup analyses, there were similar associations between the ADRB2 A46G polymorphism and hypertension risk in the hospital-based group and the Han group, but not in the population-based group or the Chinese minority group. We observed that all studies in the hospital-based group were conducted in the Han Chinese population. On the contrary, studies in the population-based group were related to different ethnic groups. The different genetic backgrounds of ethnic groups might result in great interstudy heterogeneity and negative combined results in the population-based group and the Chinese minority group.
Several limitations exist in our meta-analysis. First, we could not perform subgroup analyses of each ethnic group

Conclusion
In conclusion, ADRB2 A46G polymorphism may increase the risk of essential hypertension in the Chinese population. More studies related to the Chinese ethnic minority population should be performed to help better reveal the association between the ADRB2 A46G polymorphism and hypertension risk in different Chinese ethnic groups.

Author contributions
All authors contributed significantly to this study. Liyuan Yan and Haipeng Wang contributed equally to this work and should be considered as co-first authors. Xin Zhao, Liyuan Yan, and Haipeng Wang designed the study. Liyuan Yan and Haipeng Wang collected the data. Pengfei Liu analyzed the data. Minghan Wang and Jingjing Chen made the tables and