|Year : 2013 | Volume
| Issue : 1 | Page : 25-29
β 2 -adrenergic receptor gene polymorphisms in normal and in patients with myocardial infarction in the eastern province of Saudi Arabia
Abdullah Al-Rubaish1, Fahd Al-Muhanna1, Abdullah Al-Shehri1, Awatif Al-Nafaie2, Mohammed Shakil3, Abdullah Al-Ali4, Khalid Al-Faraidy5, Emmanuel Larbi1, Folkert Asselberg6, Amein Al-Ali7
1 Department of Internal Medicine, King Fahd Hospital of the University, Al-Khobar, Kingdom of Saudi Arabia
2 Department of Pathology, King Fahd Hospital of the University, Al-Khobar, Kingdom of Saudi Arabia
3 College of Medicine, University of Dammam, Dammam, Kingdom of Saudi Arabia
4 King Fahd Hospital, Al-Ahssa, Kingdom of Saudi Arabia
5 King Fahd Military Medical Complex, Dammam, King Fahd Hospital of the University, Al-Khobar, Kingdom of Saudi Arabia
6 Utrecht Medical Complex, The Netherlands
7 Prince Mohammed Center for Research and Consultation Studies, University of Dammam, Dammam, Kingdom of Saudi Arabia
|Date of Web Publication||3-Jun-2013|
College of Medicine, Prince Mohammed Center for Research and Consultation Studies, University of Dammam, P.O. Box 1982, Dammam 31441
Kingdom of Saudi Arabia
Introduction: Single nucleotide polymorphisms (SNPs) of the β2 -adrenergic receptor (β2 -AR) gene have been implicated in the pathogenesis of cardiovascular diseases. This study evaluated two β2 -AR SNPs in association with myocardial infarction (MI), namely arginine-glycine (G16R) substitution at codon 16 and glutamine-glutamic (Q27E) substitution at condon 27.
Objectives: Therefore, our main objective was to determine the association of these two SNPs among patients with MI with and without type 2 diabetes (T2D).
Materials and Methods: Blood samples were collected from 201 MI patients with and without diabetes and from 115 controls and the β2 -AR gene polymorphisms at codon 16 and codon 27 were assessed by restriction fragment length polymorphism. The χ2 test was used to compare differences between groups.
Results: The SNPs did not deviate significantly from Hardy-Weinberg equilibrium in the control population. The allele and genotype frequencies of the β2 -AR gene polymorphism at codon 16 (G16R) was significantly different between MI cases and controls (χ2 = 10.495, P < 0.05 and χ2 = 8.849, P < 0.05, respectively). No significant difference in genotype and allele frequencies at codon 27 was shown between these two groups (χ2 = 2.661, P ≥ 0.05 and χ2 = 1.587, P ≥ 0.05, respectively). When the MI patients with and without T2D were pooled together, genotype distribution was different between cases and controls at codon 16 (χ2 = 4.631, P = 0.099) and codon 27 (χ2 = 7.247, P = 0.027). However, no significant differences were found in allele frequencies for codon 16 and codon 27 between the two groups (χ2 = 0.628, P = 0.428; χ2 = 0.33, P = 0.565, respectively).
Conclusion: Our findings indicate a moderate association of the β2 -AR G16R gene polymorphism with MI suggesting that this gene plays a universal role in the development of MI across ethnicities. However, there was no association of β2 -AR G16R gene polymorphism with diabetic patients with MI.
Keywords: Adrenergic receptor, cardiovascular diseases, mutation, polymorphism
|How to cite this article:|
Al-Rubaish A, Al-Muhanna F, Al-Shehri A, Al-Nafaie A, Shakil M, Al-Ali A, Al-Faraidy K, Larbi E, Asselberg F, Al-Ali A. β 2 -adrenergic receptor gene polymorphisms in normal and in patients with myocardial infarction in the eastern province of Saudi Arabia. Saudi J Med Med Sci 2013;1:25-9
|How to cite this URL:|
Al-Rubaish A, Al-Muhanna F, Al-Shehri A, Al-Nafaie A, Shakil M, Al-Ali A, Al-Faraidy K, Larbi E, Asselberg F, Al-Ali A. β 2 -adrenergic receptor gene polymorphisms in normal and in patients with myocardial infarction in the eastern province of Saudi Arabia. Saudi J Med Med Sci [serial online] 2013 [cited 2020 Feb 19];1:25-9. Available from: http://www.sjmms.net/text.asp?2013/1/1/25/112913
| Introduction|| |
Cardiovascular diseases (CVDs) are the major cause of morbidity and mortality worldwide and represent a tremendous social and economic burden on society.  Several risk factors for CVD such as diet, obesity, and smoking are well defined; however, the genetic basis contributing to CVD remains obscure. Understanding the genetic basis of CVD may contribute toward identifying better targets for innovative CVD drugs. The β-adrenergic receptor belongs to the superfamily of membrane-bound G-protein-coupled receptors which is encoded by a gene on chromosome 5q31-32. , There have been many reports which suggested that a defective β2 -adrenergic receptor (β2 -AR) plays a significant role in CVDs including hypertension and myocardial infarction (MI).  A number of single nucleotide polymorphisms (SNPs) in the β2 -AR gene have been detected in many populations. , The most common SNPs are due to two missense mutations, which occur in the coding region of the intronless β2 -AR gene. The first SNP is at nucleotide 46, which causes the substitution of glycine (R) for arginine (G) at codon 16. The second SNP is at nucleotide 79, which results in the substitution of glutamic acid (E) for glutamine (Q) at codon 27. In vitro studies of these two nonsynanomous SNPs have shown that these two SNPs alter receptor function. ,,
Conclusions by recent investigations which have studied the association of these polymorphism and MI have produced conflicting results. ,,,, These conflicting conclusions may be due to different influencing factors such as study design, gender composition, and ethnicity of the study populations. 
Of the estimated 16.6 million deaths attributed to CVD worldwide, 80% of these deaths are in developing countries. CVDs are prevalent in Saudi Arabia, with the Eastern Province being reported as having one of the highest incidences.  Although the allele frequencies of these two polymorphic sites have been reported for the normal Saudi population, there is no report of whether β2 -AR polymorphisms are associated with MI in this population. , In addition, the reduction in the incidence of MI necessitates improved risk stratification and new strategies for prevention of the disease. This prompted us to carry out the present study to determine the prevalence of these polymorphic sites in normal Saudi individuals and in patients with MI with and without type 2 diabetes (T2D).
| Materials and Methods|| |
A case-control study was conducted in 199 patients with clinically confirmed MI who were residing in the Eastern Province of Saudi Arabia. All patients with MI underwent coronary angiography and diagnosis of MI was based on typical electrocardiographic changes and elevated serum enzymes. Normal subjects (115) matched with case patients for age and gender were selected at random from the general population. The sole exclusion criterion for control subjects was past or family history of MI and to be healthy at the time of blood withdrawal. Informed written consent was obtained from both patient and the control groups prior to participation in the study, which was approved by the Medical Ethics Committee. Blood samples were collected in ethylene diamine tetraacetic acid (EDTA) tubes and were frozen until analysis. Genomic deoxyribonucleic acid (DNA) was obtained from 300 μl whole blood using QIAamp Blood Kit (Qiagen, Hilden, Germany) according to the manufacturer's protocol. Genotype determination was accomplished using restriction fragment length polymorphism procedures as previously described.  Briefly, a 308 bp region of the B 2 -AR spanning both polymorphic sites was amplified. The following primers, 5' CCT TCT TGC TGG CAC CCC AT-3' (sense) and 5' GGA AGT CCA AAA CTC GCA CCA-3' (antisense) were used. The polymerase chain reaction (PCR) reaction volume of 25 μL contained 100-250 ng of DNA, 1.5 mM MgCl 2, 200 μM dNTP, and 0.25 U Tag polymerase in a standard PCR buffer. PCR cycles involved an initial 5 minutes at 94°C followed by 30 cycles at 94°C for 30 s, 58°C for 30 s followed by a final extension at 72°C for 10 minutes. The PCR product was then digested with restriction enzyme NcoI for Arg16-Gly and BbvI for the Glu27-Gln polymorphism at 45°C for 1 hour. Restriction products were separated on 3% agarose and visualized under ultraviolet (UV) illumination following ethidium bromide staining.
Genotype and allele frequencies were estimated by gene counting and expressed as percentages of the total. The χ2 test was used to compare differences between groups. A difference was considered statistically significant when P < 0.05. To study association and adjust for confounders, a logistic regression analysis was carried out. Odds ratios (OR) are given with 95% confidence interval (CI) of MI in relation to β2 -AR polymorphic genotypes.
| Results|| |
A total of 314 subjects (137 MI patients with T2D, 62 MI patients without T2D and 115 controls) were included in the study. The base line characteristics of the three study groups are shown in [Table 1]. The age and gender of the three groups were similar. The observed genotype distribution was in Hardy-Weinberg equilibrium among the controls. The genotype and allele frequencies of β2 -AR polymorphism at codon 16 (G16R) and at codon 27 (Q27E) in normal control and MI patients without T2D are presented in [Table 2].
|Table 1: Baseline characteristics of MI patients and normal control subjects|
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|Table 2: Distribution of genotype and allele frequencies of β‑adrenergic receptor at codon 16 (Arg/Gly) and codon 27 (Gln/Glu) in normal and in MI patients without T2D|
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The allele and genotype frequencies of the β2 -AR gene polymorphism at codon 16 (G16R) was significantly different between MI cases and controls (χ2 = 10.495, P < 0.05 and χ2 = 8.849, P < 0.05 respectively). No significant difference in genotype and allele frequencies at codon 27 was shown between these two groups (χ2 = 2.661, P ≥ 0.05 and χ2 = 1.587, P ≥ 0.05, respectively).
When the MI patients with and without T2D were pooled together, genotype distribution was different between cases and controls at codon 16 (χ2 = 4.631, P = 0.099), but not statistically significant, and codon 27 (χ2 = 7.247, P = 0.027) [Table 3]. However, no significant differences were found in allele frequencies for codon 16 and codon 27 between the two groups (χ2 = 0.628, P = 0.428; χ2 = 0.33, P = 0.565, respectively).
|Table 3: Distribution of genotype and allele frequencies of β‑Adrenergic receptor at codon 16 (G16R) and codon 27 (Q27E) in normal and in MI patients with and without T2D|
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| Discussion|| |
With the conclusion of the human genome project, new insight has emerged on how genes influence physiological functions involved in modulation of specific phenotype. Studies have shown that genetic polymorphisms may play an important role in the susceptibility or severity of diseases. A large number of clinical and basic research has been carried out which focused on this relationship. CVDs are caused by the complex interaction of genes and environmental factors.
The β2 -AR receptors are involved in the physiological responses such as vasodilatation, bronchial smooth muscle relaxation, and lipolysis.  The β2 -AR receptor gene is highly polymorphic and a single amino acid substitution in the structural domains critical for receptor function has been shown to result in significant changes in receptor activity. 
Nineteen polymorphisms in the β2 -AR gene have been identified, two of which (G16R and Q27E) were more frequently found in different populations with different frequencies.  Many studies have been carried out to investigate the possible relationship between these two polymorphisms and susceptibility to MI. Although some studies have shown that there is a weak association between G16R polymorphism and MI, other studies did not show such an association. ,, Moreover, studies have also shown contradicting results concerning Q27E polymorphism and its association with the development of MI. ,,
The genotype frequencies for both polymorphic sites determined in this study in normal subjects were slightly different from those previously reported.  This is probably due to intra-ethnical difference in Saudi populations residing in different areas of the Kingdom. This is confirmed by reports that have indicated that there is an ethnic difference in the frequency of these polymorphisms. 
Although there were significant differences in genotype and allele frequencies at codon 16 (G16R) between MI patients without T2D and normal control subjects (P < 0.05), there were no statistically significant differences in genotype and allele frequencies between the two groups at codon 27 (Q27E) (P > 0.05). Moreover, there were no significant differences in genotype and allele frequencies at both codons when results of MI patients with and without T2D were pooled together and compared to normal control subjects (P < 0.05). Our results of allelic frequencies at codon 16 polymorphism in MI patients without T2D are in line with those of Heckbet et al., (2003), Masuo et al., (2005), and Yuqing Lou et al., (2011) who examined the frequency of this polymorphic site of the β2 -AR gene in Americans, Australian, and Chinese population groups, respectively. ,, In addition, the allelic frequencies at codon 27 polymorphism in MI patients without T2D are in line with those of Lwamoto et al. and Gjesing et al., who examined the frequency of this polymorphic site of the β2 -AR gene in Japanese and Danish populations, respectively. ,
In summary, we present the genotype and allele frequencies of β2 -AR gene polymorphisms in normal Saudi subjects and in MI patients with and without T2D. Our findings indicate a poor association of individual SNPs with MI. However, further study is required to ascertain the interactions of different haplotypes and the response of patients with different haplotypes to various treatments.
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[Table 1], [Table 2], [Table 3]