Association Of TXA2R Gene And BDNF Gene Polymorphisms With Ischemic Stroke In A Chinese Population

Background:Stroke is the second most common cause of death worldwide. In China with1.4billion populations, the annual stroke mortality rate is approximately1.6million,which has exceeded heart disease to become the leading cause of death. Ischemicstroke (IS) is the most common type of stroke, and about43%to79%of all strokesare ischemic in China，Risk factors for IS include hypertension, atrial fibrillation,diabetes mellitus and hyperlipidemia. However, the prevalence of these conditionscould not explain the rising incidence of IS. Recent studies have demonstrated thatstroke risk is influenced by both genetic and environmental factors. Acute arterialthrombosis as a result of atherosclerosis is the major cause of IS, and plateletaggregation is known to play a key role in the development of atherosclerosis andthrombosis. TXA2is the major stimulator of platelet aggregation and a potentprothrombotic mediator in vivo. TXA2binding to its cognate receptor, TXA2R,activates signaling pathways that modulate vascular reactivity, cardiac function, andplatelet activation. Polymorphisms within human TXA2R gene have previously beenshown to be associated with IS in a Japanese and Korea population. However, the relationship between TXA2R gene polymorphisms and IS in a Chinese populationremains unknown. The first aim of our study was to determine whether geneticvariant of TXA2R was associated with IS in Chinese.IS is the major cause of serious, permanent disability requiring institutionallong-term care. But the rates and extent of recovery vary considerably betweenindividuals. This phenomenon led us to hypothesis that differences in genetic factorsmay influence an individual’s capacity for brain plasticity, thus contributing todifferent outcomes. Previous animal studies reported that BDNF exerts strongsurvival and differentiation function during the development of the nervous system.BDNF and its receptor (TrkB) have previously been used as markers of motor neuronsurvival and neuronal plasticity. BDNF also represents a crucial signaling molecule inadaptative brain plasticity after stroke. A common single nucleotide polymorphism(G196A orVal66Met) in the BDNF gene leading to a valine (Val) to methionine (Met)substitution in codon66of the prodomain affects the regulated secretion andneuroplastic effect of mature BDNF. Rencently studies have shown that the BDNFVal66Met polymorphism predicts poor outcome of aneurysmal subarachnoidhemorrhage, possibly contributing to the severity of reversible cerebralvasoconstriction syndrome (RCVS). However, no association has yet been shownbetween the BDNF polymorphism and severity,3-month functional outcome of IS.The second aim of this study was to determine whether the BDNF G196Apolymorphism will independently influence occurrence, severity,3-month functionaloutcome of IS in Chinese.Methods:A case-control design was introduced．All patients were further categorized intothe following subtypes: large artery atherosclerosis (LAA), small artery occlusion(SAO)，Cardioembolism(CE） and other strokes with rare or undetermined etiologybased on the Trial of Org10172in Acute Stroke Treatment (TOAST) classification.Age-matched control subjects were selected from individuals who have no history ofstroke or cardiovascular diseases. All patients and control subjects are Chinese.1) TXA2R gene rs768963SNPs were genotyped by polymerase chain reaction and restriction fragment length polymorphism (PCR-RFLP) analysis. BDNFgeneG196A (rs6265) SNPs were genotyped by polymerase chain reaction-ligasedetection reaction (PCR-LDR) analysis. Sequencing method confirmedgenotyping results. Data was processed by SPSS19.0statisticalsoftware．Calculations of genotype and allele frequencies were made for ISsubtype groups and control group．X2test was used to complete comparisons ofgenotype and allele distributions．Test for deviation of genotype distributionfromHardy-Weinberg equilibrium was done using the X2goodness of fit test.Conditional Logistic Regression adjusted for IS traditional risk factors includingage，hypertension, diabetes mellitus, and hypercholesterolemia. The influence ofgene polymorphisms on IS was indicated by odds ratio(OR) and95％confidence (CI) with P<0.05as significant criteria．2) The assessment of all patients was done at first day (admission day) based on theNational Institutes of Health Stroke Severity Scale (NIHSS). IS patients wereclassified into mild group (NIHSS≤6) and severity group (NIHSS≥7).308patients were assessed poststroke disability90days after the acute event usingthe modified Rankin Scale (mRS). They were classified into good recovery group(mRS≤1) and poor recovery group (mRS≥2).The distribution of the BDNFG196A genotypes among mild and the severity group,good recovery and poorrecovery group were done using X2test．Conditional Logistic Regression adjustedfor traditional factors affecting IS outcome．The influence of BDNF G196A genepolymorphisms on outcome was indicated by odds ratio(OR)and95％confidence(CI) with α<0.05as significant criteria.Results:1) The genotype frequencies of all SNPs conformed to the expectations ofHardy-Weinberg equilibrium(P>0.05)．It was suggested that the selected samplescould represent the population and were suitable for genetic analysis．2) There was a significant difference in genotype of TXA2R rs768963between the IS and control group（P=0.008), CC+TC frequencies of the IS group were higherthan the control group(P=0.017).Multiple logistic regression analysis revealed asignificant association after adjustment of hypertension, DM and hyperlipidemiaas confounding factors(（P=0.023，OR=1.533，95％CI：1.060-2.216）). Therewas a significant difference in genotype of SNP rs768963between LAA,SAOand control group(P=0.009，P=0.018).3) There were no significant differences with regard to G196A genotype and allelefrequencies between the mild group and the severity group（P=0.800）．4) The distribution of the BDNF G196A genotypes among the good recovery andthe poor recovery had significant difference. BDNF gene G196A AA genotypefrequencies of the good recovery group were higher than the poor recovery group(p=0.008，OR=0.406，95%CI：203-0.813), GG+GA frequencies of the goodrecovery group were lower than the poor recovery group(P=0.011, OR=2.014，95%CI:1.124-3.607) and after logistic regression the GA+AA difference wasstill significant(P=0.012,OR=2.134，95％CI:1.178-3.866).5) There was a significant difference in genotype of BDNF gene G196A betweenthe IS and the control group. BDNF gene G196A AA genotype frequencies ofIS group were higher than the control group((P=0.021，OR=1.541，95%CI：1.034-2.298）)， GG+GA frequencies of the IS group were lower than the controlgroup(P=0.026，OR=1.409，95%CI：1.008-1.970) and after logistic regressionthe difference was still significant(P=0.030，OR=1.473，95％CI：1.038-2.089).AA+GA frequencies of the male IS group were higher than the male controlgroup(P=0.042)．AA frequencies of the female IS group were higher than thefemale control group (P=0.021). There were no significant differences betweenthe subtype groups and the control group (P>0.05). Conclusions:1) TXA2R gene rs768963C allele might be the independent risk factors of ischemicstroke in Chinese population．2) BDNF gene G196A A allele might be the independent risk factors of ischemicstroke in Chinese population.3) There was no association between BDNF gene G196A SNP and severity ofneural function defect of ischemic stroke in Chinese population.4) The presence of the BDNF gene G196A A allele is associated with a significantlyincreased risk of having a poorer outcome in stroke，A allele might be theindependent marker of90days outcome of IS in Chinese population.