Association Research Among Candidate Genes, Clinical Symptoms And Cognitive Function In Schizophrenia

Schizophrenia is a common and serious mental disorder, which occurs in youngadulthood and whose prevalence in the general population worldwide is about1%. Itis characted by the abnormal mental functions and disturbed behaviors, whichcharacteristically appear as a series of clinical features, such as positive and negativesymptoms, and cognitive deficits. Its etiology has two mainly contributing factorsincluding environmental and genetic factors. Family, twins and adoptive studies haveprecisely indicated that genetic factors may be involved in schizophrenia. Studies ofschizophrenia on genome scanning and candidate genes have acquired many positiveresults, but most of these results produce poor replication. The clinical symptoms andcognitive functions of schizophrenia are contributed by many factors that the geneticfactors of which will be the research focus in the future.ObjectiveOne purpose of this study is to investigate the associations between schizophreniaand polymorphisms of12genes, including DBH, ACE, COMT, DRD2, CHRNA5,IL-10, IL-18, COX-2, TCF4, CACNA1C, MTHFR and GNB1L by the methods of thebioinformatics, molecular biology and biostatistics. The other purpose of this study isto examine whether these genes’ polymorphisms influence the clinical symptoms andcognitive functions in schizophrenia and healthy controls. We tried to reveal theschizophrenic predisposing genes and molecular genetic mechanism of influencingthe clinical symoptoms and cognitive functions in schizophrenia.MethodsA total of350first-episode schizophrenic patients (FEP), and567chronicschizphirenic patients (CSP) and421healthy controls were recruited. Patients withschizophrenia were recruited from the inpatient unit in Beijing Huilongguan hospitaland the control subjects were recruited from the local community. All subjects areHan Chinese and patients with schizophrenia were diagnosed according to ICD-10and CCMD-II-R. All the subjects signed informed consent and peripheral blood samples werethen taken from them. Genomic DNA was extracted from the whole blood sampleusing a DNA extraction kit (Promega, USA). The DBH rs141116007and ACE rs4340were genotyped using PCR-AFLP technology. We genotyped11polymorphic SNPson the other10genes (rs4360, rs1800497, rs3829787, rs1800872, rs1946518,rs689466, rs5275, rs2958182, rs2239050, rs1801133and rs748806) using SequenomMassArray technology.The Hardy-Weinberg equilibrium (HWE) for genotypic distributions, theassociations between all candidate SNPs and schizophrenia, the LD between pairsSNPs and haplotype were tested using the online genetic SHEsis soft. The gene-geneinteraction was tested using the MDR soft. The associations between all SNPs andthese clinical features including clinical symptoms and cognitive functions wereperformed with SPSS17.0soft.Results1, H-W equilibrium test and LD analysis(1) H-W equilibrium testThe genotypic distributions of these3SNPs (rs4340, rs3829787and rs5275)were not in HWE in FEP (all, P<0.05), and the genotypic distributions of these3SNPs (rs1800497, rs3829787and rs1801133) were not in HWE of CSP (both, P<0.05),suggesting these SNPs could be the schizophrenic susceptible SNPs or could be inclose linkaged to the schizophrenic susceptible SNPs. The genotypic distributions ofall other SNPs were in HWE in FEP (all, P>0.05), CSP (all, P>0.05) and healthycontrols (all, P>0.05). Thus this sample pool was suitable for the analysis.(2) LD analysisThe estimated LD showed that rs689466-rs5275was in a LD block.2, Analysis of case-control(1) Single SNP analysis of FEP-controlThe rs141116007and rs5275were associated with FEP. There were thesignificant differences in the allelic and genotypic frequencies between FEP and healthy controls (all, P<0.05).The rs2239050and rs3829787could be also associationwith FEP. There were the significant differences in the rs2239050allelic andrs3829787genotypic frequencies between FEP and healthy controls (both, P<0.05).(2) Single SNP analysis of CSP-controlThe rs4340、rs18001133and rs748806were associated with CSP. There werethe significant differences in the allelic and genotypic frequencies between CSP andhealthy controls (all, P<0.05). The association could be also showed betweenrs1800497and CSP. There was only a significant difference in the genotypicfrequency between CSP and healthy controls (P<0.05).(3) Haplotype analysis of case-controlThe conditional test was usd to measure the combined effect of2SNPs onCOX-2. In the study of FEP-control, we found that rs689466(C)-rs5275(A)combination as the protective haplotype was associated with FEP (P<0.05).3, The association between SNPs and clinical symptoms in schizophrenia(1) The association between SNPs and clinical symptoms in FEPThe rs141116007on DBH and rs1956518on IL-18were associated withpositive sysptoms and total score of clinical symptoms in FEP (all, P<0.05). Thers4340on ACE was associated with negative sysptoms in FEP (P<0.05).(2) The association between SNPs and clinical symptoms in CSPThe rs689466and rs5275on COX-2were associated with positive sysptoms inCSP (both, P<0.05). The rs2958182on TCF4was associated with negative sysptomsin CSP (P<0.05). The rs1956518on IL-18was associated with total score of clinicalsymptoms in CSP (P<0.05).4, The association between SNPs and cognitive functions(1) The association between SNPs and cognitive functions in healthy controlsThe rs2958182on TCF4and rs2239050on CACNA1C were associated withattention in healthy controls (both, P<0.05). The rs5257on COX-2was associatedwith language in healthy controls (P<0.05). The rs2958182on TCF4was associatedwith delayed memory and total score of cognition in healthy controls (both, P<0.05). (2) The association between SNPs and cognitive functions in FEPThe rs141116007on DBH, rs1800497on DRD2and rs5275on COX-2wereassociated with immediate memmory in FEP (all, P<0.05). The rs689466and rs5257on COX-2were associated with language in FEP (both, P<0.05).(3) The association between SNPs and cognitive functions in CSPThe rs18001133on MTHFR and rs1800872on IL-10were associated withattention in CSP (both, P<0.05). The rs2958182on TCF4and rs18001133on MTHFRwere associated with language in CSP (both, P<0.05). The rs1800497on DRD2andrs2958182on TCF4were associated with delayed memmory in CSP (both,P<0.05).The rs2958182on TCF4was associated with total score of cognitivefunctions in CSP (P<0.05).ConclusionsAbove all, it can be concluded that (1) the genetic polymorphisms of the DBH，COX-2, CHRNA5and CACNA1C genes are likely to confer susceptibility to FEP;(2)the genetic polymorphisms of the ACE，DRD2, MTHFR and GNB1L genes are likelyto confer susceptibility to CSP;（3）The DBH and IL-18genetic variation in FEP andCOX-2genetic variation in CSP influence positive clinical sympotoms;(4) The ACEgenetic variation in FEP and COX-2genetic variation in CSP influence negaitiveclinical sympotoms;(5) The DBH and IL-18genetic variation in FEP and IL-18genetic variation in CSP influence total score of clinical sympotoms;(6) TCF4,CACNA1C and COX-2genetic variations are association cognitive functions inhealthy controls;(7) DBH, DRD2and COX-2genetic variations are associationcognitive functions in FEP;(8) MTHFR, IL-10, DRD2and TCF4genetic variationsare association cognitive functions in CSP;(9) There are genetic and clinicalheterogeneous in schizophrenia.