Association Of T393C Single Nucleotide Polymorphism In The GNAS1 Gene With Non-Valvular Atrial Fibrillation

Background:Atrial fibrillation (AF), including valvular and non-valvular, is a very common arrhythmia. The incidence of atrial fibrillation increased significantly with age, and its prognosis is poor. The incidence of atrial fibrillation is about 0.5% population in 2% at the age of 60 to 69 years and 9% at the age of 80～89 years, and its fatality rate is from 1% to 3%. Atrial fibrillation was paroxysmal or persistent. Most atrial fibrillation can be secondary to organic heart disease, such as rheumatic heart disease, coronary heart disease, hypertensive heart disease, hyperthyroidism, constrictive pericarditis, cardiomyopathy, infective endocarditis, and chronic pulmonary heart disease. AF is also found in normal subjects, can be induced by emotional, surgery, exercise, or acute alcoholism. Heart and lung disease in patients with acute hypoxia, hypercapnia, metabolic or hemodynamic disorder can also cause AF.Some pataients are absent of clinical findings of cardiac abnormalities and palimony discase, this condition is known as lone atrial fibrillation. Some elderly patients with atrial fibrillation are shown with bradycardia-tachycardia syndrome, tachycardia of performance. The percentage of Valvular and Non-valvular atrial fibrillations accounted for 12.9% and 87.1%, respectively. Non-valvular atrial fibrillation is defined as a type of AF without value diseases.Atrial fibrillation with circulation embolism is very dangerous. Emboli come from the left atrium due to blood stasis caused by loss of atrial contraction, and AF in patients with Non-valvular heart disease atrial fibrillation, the stroke risk was higher than those without AF. Mitral valve prolapse or mitral stenosis with AF easily causes cerebral embolism. Whether or not the lone atrial fibrillation increase in the incidence of stroke. It is not unanimous. At present, AF is treated with antiarrhythmic drug therapy and radiofrequency ablation or a combination of them. However, poor efficacy of drug therapy and drug safety problems exist. Recently, pulmonary vein isolation has become standard treatment of AF. Although pulmonary vein isolation is more effective than antiarrhythmic drug therapy, but there is still relapse, and AF patients need repeated treatment. AF is a multifactorial disease with complex pathogenesis, which is still not completely clear. Atrial electrical remodeling and structural remodeling is an important mechanism for the development of AF. Neuroendocrine abnormalities may be the core mechanism of atrial remodeling in AF. Renin-angiotensin system (RAS) and the autonomic nervous system (ANS) activation are two factors key. ANS plays an important role in the maintenance of atrial fibrillation and its ablation. ANS may causes the release of neurotransmitters. Then the neurotransmitters are combined with the corresponding receptors and regulate the permeability of cardiac ion channels to regulate the electrical activity of the heart. Postganglionic sympathetic fibers release norepinephrine, which combines withβ-receptors in cardiac cells and activates these receptors cAMP form ATP. After P-receptor stimulation, is activated through the activation of Gs protein a subunit coupled toβ-AR, cyclic adenosine enzyme (AC), and promotes the formatim of cAMP, as an intracellular second messenger, and then regulates a series of cellular effects by activating protein kinase A (PKA). G protein are important signal transduction molecules. At present, G proteins are divided into Gs, Gi, Gq and G12 four categories, made up ofα,βandγsubunits. The main function of G protein is to transfer the extracellular signaling to the intracellular. There are two types of G protein conformation, one type is of a non-activated protein, made up ofαβγtrimer combined with GDP the existence; the other is activated, made up of GTP binding a subunit with dissociatin of Py dimer. Human Gs a subunit gene (GNAS1) is located on chromosome 20q13.2-13.3. There is a silent single nucleotide single nucleotide mutation in exon 5,393 gene, and the codon encoding isoleucine is changed into the ATT ATC (ATT→ATC, Ilel31), and leads to enhancement of AC activity.In 1965, heart rate variability (HRV) analysis is discovered by Honand and Lee and first used in clinical. HRV is an effective non-invasive method to detect regulatory function of the autonomic nervous. In the present Holter HRV analysis, uses the linear detection range and time domain frequency domain method. It has the neural and humoral cardiovascular regulation of large amounts of information. HRV can quantitatively reflect activity and its regulatory function of the autonomic nervous system. After analyzing the data, it information on the autonomic nervous system is obtained, assess to the cardiovascular autonomic nerve tension, balance and its activities quantitatively. It is very important in clinical to. All normal 24h time domain standard deviation of RR intervals (SDNN) reflects the changes in autonomic nervous activity. Every 5min within 24h the RR interval standard deviation (SDANN) reflect changes of sympathetic tone. The percentage of successive RR interval differences is reprensed by PNN50> 50ms is more sensitive to changes in vagal tone. In the frequency domain analysis, low frequency power (LF) reflects the role of the autonomic nervous, mainly the role of sympathetic nerve. High frequency power (HF) mainly reflects the role of vagus nerve. ANS participated in the occurrence maintenance of AF, but the relationship between GNSA1 gene polymorphism and sympathetic nerve activity is unclear. So GNSA1 gene was chosen as the gene of the study. We collect blood samples with non-valvular atrial fibrillation in patients, and observe the HRV indexes, and then further explore the GNAS1 gene T393C single nucleotide polymorphism (SNP) with non-valvular atrial fibrillation relevance. Our aims is to provide a basis for the future of non-valvular atrial fibrillation gene diagnosis and gene therapy.Objectives:1.To analyze the correlation of GNAS1 gene T393C SNP in Han Chinese with non-valvular AF, and indentify the clinical significance of the SNP sites.2.To investigate relation the GNAS1 gene T393C and the sympathetic nerve activity.3.To explore the mechanism of SNS on the occurrence and maintenance of non-valvular AF.Subjects:In March 2011 to April 2011 period, I learned from the total of 81 cases were selected from the First Affiliated Hospital of Jinan University. Selected population were checked by history taking, physical examination, laboratory tests (blood, urine, then normal, blood lipids, blood glucose, liver and kidney function), and cardiac ultrasound. This will assure the condition match between the case group and control group.Case group consisted of 41 patients, including 20 males and 21 females, aged 65.15±10.97 (38-85) years old. Inclusion criteria:①resting 12-lead ECG,24h Holter tests suggested AF without other arrhythmias;②ECG, chest radiography, echocardiography, biochemical function, myocardial enzymes, some of coronary angiography and other tests ruled out high blood pressure, coronary heart disease, dilated and hypertrophic cardiomyopathy, arrhythmogenic right-oriented ventricular cardiomyopathy, valvular heart disease and other organic heart disease;③ruling out sick sinus syndrome, a long RR interval, II or high degree atrioventricular block and other arrhythmias;④ruling out electrolyte imbalance and metabolic diseases such as rheumatoid arthritis, diabetes and other diseases.A total of 40 patients in control group, including 20 males and 20 females, at the age of 65.45±11.02 (39-88) years old. Inclusion criteria:No AF and other arrhythmias, in accordance with the above-mentioned exclusion criteria.Methods:Two sets of clinical data of patients were established by observation table, including detailed records of patient age, gender, height, weight, smoking, alcohol consumption and heart rate. All subjects underwent 12-lead resting ECG,24h Holter test, and record the 24-hour average heart rate, SDNN, SDANNindex, SDNNindex, rMSSD, pNN50, LF, HF and LF/HF. From all the patients fasting venous blood were collected, and blood was put into tubes with EDTA anticoagulant in full bloom. According to the kit instruction was extracted from peripheral blood cells deoxyribose nucleotides (DNA). Blood-packing was stored in -40℃. GNAS1 gene T393C SNP was by all subjects by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) sites determined. Abnormal DNA was detected by agarose gel electrophoresis electrophoresis. Finally, GNAS1 variations were determined by anaylysis of DNA sequencing. Genotypes between the two groups were compared, and allele frequency distribution characteristics of the relationship with the HRV were also studied.Results:1.The T393C SNP of the GNAS1 gene was identified in Han Chinese PCR-RFLP. 2.The frequencies of genotype of TT, TC, CC in case group was 8,17,16 and 21,13,6 in control group respectively. The difference between the two groups was statistically significant (χ2=10.896,P=0.004). The frequencies of genotype of Fokl-allele, and FokI+ allele in case group and control group were 33,49 and 55,25, repectively. The frequencies of Fokl- allele, Fokl+ allele were 40.24%,59.76% in case group and 68.7%,31.25% in control group, respectively. The difference between the two groups was statistically significant (χ2=13.261, P<0.05). FokI+ allele frequencies in case group were higher than those of control group.3.Compared to TT genetype, CC homozygous, TC+CC genotype significantly increase the risk of non-valvular AF. The odds ratios(OR) are 7.000(2.021-24.246), 4.559(1.693-12.280), P values are 0.002,0.003, respectively. The OR values (95% CI) of heterozygous genotype TCare 3.433 (1.156～10.193),and the P value is 0.026.4. The median of LF/HF in the case group and the control group is 14.5 and 10.61, respectively. The difference between the two groups was statiscally significant (the mean rank of LF/HF is 26.61 vs 55.04, P<0.05).5.The difference of LF/HF, among the genotypes TT,TC,CC is statistically significant(χ2=22.546, P<0.05). The mean rank of them is 27.53,40.73,59.11 respectively, that is CC>TC>TT. PNN50,LF,LF/HF among the three genotypes was significant difference (P<0.05).Conclusions:1.The T393C SNP of GNAS1 gene exists in Han Chinese.2. SDNN, rMSSD, pNN50, LF,HF and LF/HF in the case group are higher than those of the control group. It is suggested that activity of sympathetic nerve and vagal nerve is increased.3.The T393C polymorphism of GNAS1 is closely associated with non-valvular AF in the Han Chinese. Fokl+allele may be the predisposing factor. 4.There is a close correlation between the T393C SNP of GNAS1 gene and LF/HF. That is CC>TC>TT.5.The underlying mechanism of non-valvular AF caused by T393C SNP:The Fokl+ allele variant of the Gs protein may cause its functional variant, and enhances activation of AC, resulting in increased cAMP level and PKA activity, and finally may increase the risk of incidence AF.