| Abstract | Aberrant synaptic dysfunction is implicated in the pathogenesis of schizophrenia. The DLGAP2 gene encoding the SAP90/PSD-95-associated protein 2 (SAPAP2) located at the post-synaptic density of neuronal cells is involved in the neuronal synaptic function. This study aimed to investigate whether the DLGAP2 gene is associated with schizophrenia. We resequenced the putative promoter region and all the exons of the DLGAP2 gene in 523 patients with schizophrenia and 596 non-psychotic controls from Taiwan and conducted a case-control association analysis. We identified 19 known SNPs in this sample. Association analysis of 9 SNPs with minor allele frequency greater than 5% showed no association with schizophrenia. However, we found a haplotype (CCACCAACT) significantly associated with schizophrenia (odds ratio:2.5, p<0.001). We also detected 16 missense mutations and 1 amino acid-insertion mutation in this sample. Bioinformatic analysis showed some of these mutations were damaging or pathological to the protein function, but we did not find increased burden of these mutations in the patient group. Notably, we identified 5 private rare variants in 5 unrelated patients, respectively, including c.-69+9C>T, c.-69+13C>T, c.-69+47C>T, c.-69+55C>T at intron 1 and c.-32A>G at untranslated exon 2 of the DLGAP2 gene. These rare variants were not detected in 559 control subjects. Further reporter gene assay of these rare variants except c.-69+13C>T showed significantly elevated promoter activity than the wild type, suggesting increased DLGAP2 gene expression may contribute to the pathogenesis of schizophrenia. Our results indicate that DLGAP2 is a susceptible gene of schizophrenia. |
| Abstract | The Consortium on the Genetics of schizophrenia Family Study (COGS-1) has previously reported our efforts to characterize the genetic architecture of 12 primary endophenotypes for schizophrenia. We now report the characterization of 13 additional measures derived from the same endophenotype test paradigms in the COGS-1 families. Nine of the measures were found to discriminate between schizophrenia patients and controls, were significantly heritable (31 to 62%), and were sufficiently independent of previously assessed endophenotypes, demonstrating utility as additional endophenotypes. Genotyping via a custom array of 1536 SNPs from 94 candidate genes identified associations for CTNNA2, ERBB4, GRID1, GRID2, GRIK3, GRIK4, GRIN2B, NOS1AP, NRG1, and RELN across multiple endophenotypes. An experiment-wide p value of 0.003 suggested that the associations across all SNPs and endophenotypes collectively exceeded chance. Linkage analyses performed using a genome-wide SNP array further identified significant or suggestive linkage for six of the candidate endophenotypes, with several genes of interest located beneath the linkage peaks (e.g., CSMD1, DISC1, DLGAP2, GRIK2, GRIN3A, and SLC6A3). While the partial convergence of the association and linkage likely reflects differences in density of gene coverage provided by the distinct genotyping platforms, it is also likely an indication of the differential contribution of rare and common variants for some genes and methodological differences in detection ability. Still, many of the genes implicated by COGS through endophenotypes have been identified by independent studies of common, rare, and de novo variation in schizophrenia, all converging on a functional genetic network related to glutamatergic neurotransmission that warrants further investigation. |