An Association Study Between The NCAM1 Gene And Early Onset Schizophrenia

Schizophrenia, SZ (MIM 181500) is a severe mental disorder characterized by hallucinations,delusions, flat and or inappropriate affect, and cognitive impairment. Worldwide prevalence shows a lifetime risk of approximately 1% and has a strong genetic component. However, the mode of transmission is complex, multiple genes of modest or small effect and rare deleterious variants with large effect are both likely in schizophrenia predisposition. Over the last two decades, linkage and association studies have identified a number of chromosomal regions and several promising candidate genes. Compared with adult-onset form of the disorder (AOS), childhood-onset schizophrenia (COS) and adolescent schizophrenia have a severe, progressive course. Ascertainment of these cases may facilitated the identification of causal genetic variants.The neural cell adhesion molecule1 (NCAM1) has been considered as a susceptibility gene for schizophrenia and bipolar disorder. NCAM1 is located on human chromosome 11q23.1 and is a multifunction transmembrane protein which plays an important role in cell differentiation and migration, neurite outgrowth, establishment of specific patterns of synaptic connections, synaptic plasticity and long-term potentiation.ObjectiveStudy the association between the NCAM1 gene and early onset schizophreniaMethodsStage1:Case-control DNA pooling genome-wide association study A total of 89 childhood and adolescent onset patients were recruited from the Department of Child and Adolescent Psychiatry, Shandong Mental Health Center ( 2005-2008 ). The average age of the cases was 16.14±2.77 and the average age of onset was 15.15±2.80. The male/female ratio was 1: 0.98 (45/44). A total of 1000 healthy controls were blood donors from the Blood Center of Shandong Province. The average age of the controls was 23.08±5.67, and the male/female ratio was 1.32:1(569/431). The controls were not screened for mental illness. Genomic DNA was extracted and two DNA pools from 89 cases and 1000 controls were constructed respectively by adding up 10 ul of each sample. Two Affymetrix Genome-Wide Human SNP Array 6.0 containing 906,600 SNPs were applied for genotyping of the two DNA pooling samples. Association study based on case-control study was performed.Stage2:Genotyping of SNPs in NCAM1 by High Resolution Melting (HRM)-(Family-based study)A total of 100 nuclear families of childhood and adolescent onset schizophrenia were recruited from the Department of Child and Adolescent Psychiatry, Shandong Mental Health Center (2005-2010). 86 families had both parents were available (trios) and the remaining 14 families had only a single parent were available (parent-offspring pairs). The average age of the cases was 16.61±3.06 and the average age at onset was 15.66±3.16. The male/female ratio was 1:1.13 (47/53). The 89 patients for DNA pooling genome-wide association study were included in the 100 nuclear families. Then, six SNPs (rs10891495, rs1245133, rs1821693, rs686050, rs12794326, rs674246)were choosen and genotpyed by High Resolution Melting (HRM). Transmission disequilibrium tests(TDT) was performed for the data analysis.The criteria for diagnosing schizophrenia were made according to DSM- IV. Cases and controls are all come from the Chinese Han population in Shandong peninsula.ResultsThe data analysis of the two DNA pooling samples genotyped by Affymetrix Genome-Wide Human SNP Array 6.0 revealed that rs10891495 ( Affymetrix No. SNP_A2072123 )was associated with childhood and adolescent onset schizophrenia (χ2 = 23.66, P=0.000(1.15E-06). This SNP is just within the NCAM1 gene.The data analysis of the six SNPs (rs10891495, rs1245133, rs1821693, rs686050, rs12794326, rs674246) genotyped in the 100 nuclear families were all in Hardy–Weinberg equilibrium. Neither single-marker nor haplotype analysis support an association between these six SNPs and schizophrenia. In the linkage disequilibrium (LD) analysis, only two SNPs (rs1943620, rs686050) spaced about 7 kb apart were detected in strong LD (D'=0.98) within the 100 families.Conclusions:Our result indicate that these six SNPs (rs10891495, rs1245133, rs1821693, rs686050, rs12794326, rs674246) of the NCAM1 may not make a major contribution to the genetic susceptibility to childhood and adolescent onset schizophrenia in the Chinese Han population. However, the validation in different locations, populations and exploration of protein, methylation and transcription of NCAM1 in schizophrenia are still needed.As one of the most complicated polygenetic disorder,schizophrenia has been a hot spot for the researchers and institutes. Multiple genes are taking effect in a comprehensive way that it is hard to catch a single gene with significance statistic power.Before GWAS emerged, most gene association studies were applied with the tests of candidate gene involvement. Approximately 800 genes have been tested for association. Unfortunately,none of them as of today can be considered fully established. The common issues are lack of sufficient statistical power and hard to replicate.But GWAS has it's limitations as come to the stratifications.So the method for following up GWAS results needs to be thorough; replication and fine mapping of associated regions are necessary for further progress.