Study Of The Genetic Association Between The Polymorphism Of Cytosolic PLA2 Family Genes And Schizophrenia

Schizophrenia is a common and serious mental disorder, whose pathogenesisremains undefined. Family, twin, and adoptive studies have precisely indicated agenetic component may be involved in schizophrenia. The studies ofschizophrenia on genome scanning and candidate gene have acquired manypositive results, however, these results with poor repeats have caused muchdisputation. So far, the major and specific susceptibility genes leading toschizophrenia remains unidentified.ObjectiveTo investigate a genetic association between the polymophism of cytosolicphospholipase A2 ( cPLA2 ) family genes and schizophrenia by detecting SNPsof cPLA2 family genes with the bioinformatics and the molecular genetics. Thepresent study tried to reveal the predisposing genes and molecular geneticmechanism for schizophrenia.MethodsA total of 240 Chinese parent–offspring trios of Han descent, consisting offathers, mothers, and affected offspring with schizophrenia, were recruited forthe genetic analysis. These subjects originally came from Siping and Kaixuanpsychiatric hospital. The patients ( 165 males and 75 females ) were admitted toa psychiatric hospital during the period between 2000 and 2005. They werediagnosed as having a schizophrenic illness using the International StatisticalClassification of Diseases and Related Health Problems, Tenth Revision( ICD-10 ) and Chinese classification and diagnostic criteria of mental disorders,the second revised edition ( CCMD-II-R ).The diagnosis was made independently by at least two psychiatrists. All thesubjects gave written informed consent for the genetic analysis and taken bloodfrom peripheral vein. Genomic DNA used for PCR amplification was extractedfrom the whole blood sample using a DNA extraction kit ( Promega, USA ). Wescreened polymorphic SNPs using PCR-RFLP analysis based on the SNP map ofthe genes for cPLA2. We genotyped 11 SNPs in 240 family trios, includingBan ⅠS NP at PLA2G4A locus, rs1648833 at PLA2G4B locus, rs1366442,rs1549637 at PLA2G4C locus, rs2459692, rs4924618 at PLA2G4D locus,rs2235346, rs2272831, rs2284060 at PLA2G6 locus and rs4665135, rs2203053at PLA2R1 locus.The Hardy–Weinberg equilibrium for genotypic distributions was testedusing the chi-square ( χ2 ) goodness-of-fit test. The haplotype relative risk test( HRR ) and transmission disequilibrium test ( TDT ) were performed with theSPSS12.0 program. The HRR and TDT were applied to test allelic associationfor a single locus. The conditional test was performed with the UNPHASEDprogram ( Frank Dudbridge, MRC Human Genome Mapping Project ResourceCentre, Hinxton, UK ). The conditional test was used to test the combined effectof distinct loci on the disease by conditioning on allele ( COA ) or byconditioning on genotype ( COG ). The χ2 test was used to test the associationbetween the SNPs of cPLA2 family genes and clinical symptoms of schizophrenia.Results(1)The analytic results of questionaire dataThe analytic results showed that first age of onset of schizophrenia wasbetween 13 and 39 yeares old, the mean of age of onset was 21.72 ± 5.109years old. Most schizophrenia ( 128 ) onset at 20 ~ 29 years old firstly. Therewere no difference between the male and female schizophrenia with firt age ofonset, course of disease and positive family history ( t = 0.901, P = 0.369;t =0.140, P = 0.889;χ2 = 1.098, P = 0.295 ). There was significant differencebetween the male and female schizohrenia at the positive clinical symptoms ofexperience of being revealed, delusion of love, other delusion, illogic of thinkingand bizarre behavior ( P < 0.05 ). The incidence rate of the five positive clinicalsymptoms were higher in female schizophrenia than in male schizophrenia.There was no significant difference between the male and female schizophreniain the negative and other positive clinical symptoms. Premorbid personality ofmost schizophrenia was introvert ( 215 ) and there was sex differences. Mostschizophrenia were paranoid and undifferentiated type and there was no sexdifferences.(2)Hardy-Weinberg equilibrium testThe Hardy–Weinberg equilibrium for genotypic distributions was testedusing the chi-square ( χ2 ) goodness-of-fit test. The goodness-of-fit test showedthat the genotypic distributions of the 11 SNPs were in Hardy-Weinbergequilibrium in both the patient group and the parent group ( P > 0.05).(3)HRR analysisIn total samples, HRR analysis showed that there was significant differencefor the frequencies of alleles of rs1549637 at PLA2G4C locus between the caseand the control ( χ2 = 5.341, P = 0.021 ). This indicated an association betweenrs1549637 and schizophrenia.In male schizophrenia, there was significant difference for the frequenciesof alleles of rs1648833 at PLA2G4B locus and rs1549637 at PLA2G4C locusbetween the case and the control ( χ2 = 4.583, P = 0.032;χ2 = 4.876, P = 0.027 ).This indicated an association between rs1648833, rs1549637 and maleschizophrenia. In female schizophrenia, there was significant difference for thefrequencies of alleles of Ban ⅠS NP at PLA2G4A locus between the case and thecontrol ( χ2 = 5.337, P = 0.021 ). This indicated an association betweenBan ⅠS NP and female schizophrenia.In paranoid schizophrenia, there was significant difference for thefrequencies of alleles of rs1549637 at PLA2G4C locus, rs2272831 at PLA2G6locus and rs4665135 at PLA2R1 locus between the case and the control ( χ2 =5.362, P = 0.021;χ2 = 5.590, P = 0.018;χ2 = 3.939, P = 0.047 ). This indicatedan association between rs1549637, rs2272831, rs4665135 and paranoidschizophrenia. In undifferentiated schizophrenia, there was no significantdifference for the frequencies of alleles of these 11 SNPs between the case andthe control ( P > 0.05 ). This indicated no association between these 11 SNPsand undifferentiated schizophrenia.(4)TDT analysisIn total samples, TDT analysis showed that the probability of the twodifferent alleles from heterozygous parents deviated from 50% at rs1549637 ofPLA2G4C locus ( χ2 = 5.633, P = 0.018 ). This indicated an association betweenrs1549637 and schizophrenia.In male schizophrenia, the probability of the two different alleles fromheterozygous parents deviated from 50% at rs1648833 of PLA2G4B locus andrs1549637 of PLA2G4C locus ( χ2 = 4.481, P = 0.034;χ2 = 5.263, P = 0.022 ).This indicated an association between rs1648833, rs1549637 and maleschizophrenia. In female schizophrenia, the probability of the two differentalleles from heterozygous parents deviated from 50% at BanⅠ SNP ofPLA2G4A locus ( χ2 = 4.688, P = 0.030 ). This indicated an association betweenBan ⅠS NP and female schizophrenia.In paranoid schizophrenia, the probability of the two different alleles fromheterozygous parents deviated from 50% at rs1549637 of PLA2G4C locus,rs2272831 of PLA2G6 locus and rs4665135 of PLA2R1 locus ( χ2 = 5.677,P = 0.017;χ2 = 5.333, P = 0.021;χ2 = 4.762, P = 0.029 ). This indicated anassociation between rs1549637, rs2272831, rs4665135 and paranoid schizophrenia.In undifferentiated schizophrenia, the probability of the two different alleles fromheterozygous parents didn't deviate from 50% at these 11 SNPs ( P > 0.05 ).This indicated no association between these 11 SNPs and undifferentiatedschizophrenia.(5)Analysis of the combined effect of distinct lociThe conditional test was used to test the combined effect of distinct loci onthe disease by COA or by COG. No matter in total samples or in different sexgroups and different clinical classification groups, both the COA and COG testshowed a disease association for Ban Ⅰ SNP ( PLA2G4A ), rs1549637( PLA2G4C ), rs2459692 ( PLA2G4D ) and rs4665135( PLA2R1 ) combinedwith other different SNPs. This indicated that there were more than one SNPsassociated with schizophrenia in cPLA2 family genes.(6)Association between the allele, genotype of SNPs and clinical symptomsNo matter in total samples or in different sex groups and different clinicalclassification groups, both allelic and genotypic association test with clinicalsymptoms showed that different SNPs of the 11 SNPs associated with differentclinical symptoms and some SNPs associated with two or more than twodifferent clinical symptoms;At the same time, the results showed that someclinical symptoms associated with two or more than two different SNPs. Thisindicated that there were many SNPs associated with clinical symptoms ofschizophrenia in cPLA2 family genes and schizophrenia had the clinical andgenetic heterogeneity.ConclusionsAccording to the above-mentioned analytic results, we can reach thefollowing conclusions: ① There is a genetic association between the PLA2G4C( rs1549637 ) locus and schizophrenia. ② The PLA2G4B ( rs1648833 ) andPLA2G4C ( rs1549637 ) loci associate with male schizophrenia;The PLA2G4A( BanⅠ SNP ) locus associates with female schizophrenia;③ The PLA2G4C( rs1549637 ), PLA2G6 ( rs2272831 ) and PLA2R1 ( rs4665135 ) loci associatewith paranoid schizophrenia;④ There are many loci in the cPLA2 family genes,which associate with the schizophrenic clinical symptoms;⑤ There is no sexdifference at the first age of onset, course of disease and positive family history;⑥ The female schizophrenia has more positive clinical symptoms;⑦ There isa sex difference at the predisposing genes of schizophrenia;⑧ Schizophrenia isa polygenic inheritance disease and has the clinical and genetic heterogeneity.In a word, these findings thoroughly suggest that cPLA2 genes associatewith schizophrenia, which support the metabolic disorder hypothesis of nerve cellmembrane phospholipids powerfully. The genetic association of combined effectof distinct loci with schizophrenia support the polygenic theory of complexdisease. At the same time, these findings prove that schizophrenia has the clinicaland genetic heterogeneity.This study is one of the important contents of disease genomics inpost-genomic era, which has made use of the findings of HGP and supplementedto it as well. These findings will contribute to elucidate the etiology andmechanism of schizophrenia. The current study will also provide study strategyand precious experience for other complex genetic disorders.