Association Of DISC1 Polymorphisms With Late-onset Alzheimer's Disease In Northern Han Chinese

Objective:Alzheimer's disease(AD),one of the neurodegenerative disorders,is the most common form of dementia in the elderly up to now,which is characterized by the loss of massive neurons and synapses,the forming of amyloid plaques,and the generation of intracellular neurofibrillary tangles.In recent years,with the increase of aging population,the prevalence of AD is increasing?It has seriously affected the daily life,physical and mental health of the elderly.At the same time,it has brought enormous economic burden and severe mental burden to their families and society.The disrupted-in-schizophrenia-1(DISC1)is a candidate gene for psychiatric diseases and plays various roles in brain development.It has been reported as a candidate gene for AD in a recent large genomewide association study in Caucasians.Three single-nucleotide polymorphisms(SNPs)rs3738401,rs6675281 and rs821616,as non-synonymous variations of DISC1 located on Chromosome 1,have been reported to affect APP C-terminal processing and A? peptide generation,the brain development and the regulation of Wnt/GSK3? signaling pathway.In this study,we firstly interpreted the association between AD and the three SNPs within DISC1 in Northern Han Chinese.Methods: 2318 subjects have been investigated in our study,including 978 sporadic LOAD patients and 1340 healthy control subjects matched for age and gender.All the subjects were unrelated Northern Han Chinese residents,which are located in Shandong Province.The patients were diagnosed by at least two neurologists based on the diagnostic criteria of the National Institute of Neurological and Communication Disorders and Stroke–Alzheimer Disease and Related Disorders Association.All patients were identified as sporadic because none of a family history of dementia was reported.The family history and age at onset of patients were determined by their caregivers.The control subjects were enrolled with the criterion described elsewhere.Informed consent was achieved from all subjects or their caregivers.Genomic DNA was extracted from peripheral blood leukocytes using the Tiangen(Beijing,China)genomic DNA purification kit based on the manufacturer's protocol.The SNPs of DISC1 were selected depended on the previous described criteria.Genotyping of DISC1 polymorphisms(rs3738401,rs6675481 and rs821616)was determined by a SNPscanTM kit(Genesky Biotechnologies Inc.,Shanghai,China),a patented SNP genotyping technology by Genesky Biotechnologies Inc.,which was in accordance with double ligation and multiplex fluorescent polymerase chain reaction(PCR)The Hardy–Weinberg equilibrium(HWE)was tested for each SNP using genotype data from all the subjects.Deviations of the basic information for AD patients and control subjects were assessed by the Student-t test or the ?2 test.Differences in genotype and allele frequencies of the two groups were examined by Pearson ?2 test or Fisher's exact test.Assessing the associations between SNPs and AD was used odds ratio(ORs)and the 95% confidence interval(CI)by multivariate logistic regression,adjusted for age,gender and APOE ?4 status.We established 3 genetic models-dominant,additive and recessive-for each SNP according to the minor allele of these SNPs.Dominant were defined as 1(aa+Aa)versus 0(AA).Recessive were defined as 1(aa)versus 0(AA + Aa)and additive were defined as 0(AA)versus 1(Aa)versus 2(aa)(A: major allele;a: minor allele).All statistical analyses were accomplished by SPSS 16.0 software.P<0.05 was considered as a significant level for all statistical tests.In our study,we also calculated the false discovery rate(FDR)in studywide level by permutation method.The FDR was set to be 0.05.Linkage disequilibrium(LD)structure and the haplotype analysis were tested by Haploview 4.2.Estimation of the statistical power was calculated by STPLAN 4.3 software.Results: No significant differences were observed for gender(P=0.078)and age(P=0.196)in 978 LOAD and 1340 control subjects.As expected,the significant differences between LOAD and control subjects were observed in MMSE scores and Apo E ?4 allele frequency.The distributions of the 3 SNPs was in HWE(P>0.05)for controls.The analysis of allele frequencies displayed that the minor allele(T allele)at rs6675281 was associated with an increased risk of LOAD(OR=6.214,95%CI=2.100–18.398,P<0.001).Based on the frequency of the minor alleles in controls,our sample size had more than 80% power to detect the OR of rs6675281 in this study,at a significance level(alpha)of 0.05.In the total sample,the significant genotype frequency differences were shown in rs6675281(P<0.001)and rs821616(P=0.006).To rule out confounding effects in our initial association analyses,we used a logistic regression analysis adjusting for gender,age,and APOE ?4 status to reevaluate the effect of each SNP on LOAD risk.The rs6675281 was observed to significantly increase the risk of LOAD via a dominant model in total sample(OR=7.039,95%CI=2.366–20.939,PFDR=0.004)and in APOE ?4 noncarriers(OR=6.594,95%CI=2.194–19.819,PFDR=0.004).In addition,we explored the effects of the interaction between DISC1 polymorphisms and APOE genotype on the risk for LOAD,and no SNP * APOE interaction was observed here.To further investigate whether the presence of the APOE ?4 allele significantly influenced the role DISC1 in LOAD,we stratified the data according to Apo E ?4 status.In Apo E ?4 noncarriers,the genotype distribution of rs6675281 and rs821616 had a significant difference in two groups(P<0.001;P= 0.018,respectively).For rs6675281,the minor allele(T allele)differed significantly between the two groups(OR=6.655,95%CI=2.220–19.947,P<0.001).In Apo E ?4 carriers,no association was shown between the two groups.Moreover,the rs6675281 was observed to significantly increase the risk of LOAD adjusting for gender and age in APOE ?4 noncarriers(OR=6.594,95%CI=2.194–19.819,PFDR=0.004).The three polymorphisms are not in Linkage disequilibrium(for rs3738401 and rs821616,D'=0.022,r2=0.0;for rs3738401 and rs6675281,D'=0.258,r2=0.0;for 6675281 and rs821616,D'=0.022,r2=0.0).Conclusions: Our studies demonstrated significant associations between DISC1 polymorphisms and susceptibility to LOAD in Northern Han Chinese population.Among the DISC1 SNPs investigated in this study,rs6675281 seemed to be most related to LOAD risk.The association needs to be replicated in sufficiently large cohorts and in different ethnic populations,because the variations of heredity are diverse in different ethnic and geographical origin.