Further evidence for the association between G72/G30 genes and schizophrenia in two ethnically distinct populations

Recently, the nested genes G72 and G30 on chromosome 13q32-q33 have been implicated in the etiology of schizophrenia. We genotyped six single-nucleotide polymorphisms (SNPs: rs3916965, rs3916967, rs2391191, rs778294, rs779293 and rs3918342), which span approximately 82.5 kb in the region encompassing the G72/G30 genes in 1176 Han Chinese subjects (588 cases and 588 controls) and 365 Scottish subjects (183 cases and 182 controls). Significant association between an allele of marker rs778293 and schizophrenia was found in our Chinese samples (P = 0.0013), and was replicated in the Scottish samples (P = 0.022). LD analysis revealed that four SNPs between rs3916965 and rs778294 were in LD, called block I, and the two distal SNPs (rs778293 and rs3918342) constituted a block II in both the Chinese and Scottish samples. We selected one SNP from each block (rs778294 from block I and rs778293 from block II), and then analyzed the haplotypes. A significant difference was observed for the common haplotype GC in the Chinese sample (P = 0.0145), and was replicated in the Scottish sample (P = 0.003). On meta-analysis, we separately analyzed the studies in Asian and European populations because of significant heterogeneity in the homogeneity test. We found a statistically significant association between rs778293 and schizophrenia in Asian populations, but no difference was found between cases and controls in the European populations. Overall, our data give further support to the existing evidence that G72/G30 genes are involved in conferring susceptibility to schizophrenia.

Family-based association study of Epsin 4 and Schizophrenia

Recently, Pimm et al. identified Epsin 4 on chromosome 5q33 as a susceptibility gene for schizophrenia in the British population, based on linkage and association evidence. In Pimm's case-control study, both the single polymorphisms and the individual haplotypes at the 5' end of the gene showed genetic association with schizophrenia. Here, we report the first study evaluating the relevance of Epsin 4 and schizophrenia outside the British population. Markers showing positive results in the original work as well as two additional polymorphisms were genotyped in 308 Han Chinese family trios. Transmission disequilibrium analysis was used to test for association of single-locus markers and multi-locus haplotypes with schizophrenia. Although no individual marker was significant at the P=0.05 level, the haplotypes detected in our samples, different from those previously reported, showed strong evidence of association (most significant global P=0.0021). Our results indicate the presence of a locus near the 5' end of Epsin 4 conferring susceptibility to the disease and provide further support for Epsin 4 as an important potential contributor to genetic risk in schizophrenia.

Interleukin-10 −1082 promoter polymorphism is associated with schizophrenia in a Han Chinese sib-pair study

The interleukin-10 (IL-10) gene has been identified as a susceptibility gene for schizophrenia in Caucasians. A previous case-control study conducted by our group revealed a weak association between polymorphism, -592C/A, of the IL-10 gene promoter and schizophrenia. Our present study was aimed at confirming the association of the IL-10 promoter with schizophrenia using 197 Han Chinese sib-pair families. A family-based association test (FBAT) and haplotype analysis was undertaken using the FBAT v1.5.5. The global TDT was significant for a different polymorphism, -1082G/A (chi2=13.16, P=0.000285) and that the allele -1082G was preferentially transmitted to schizophrenia-affected children. Furthermore, haplotype TDT analysis showed that haplotype "GCC" was significantly associated with the disease (chi2=8.1, P=0.00443). Our results also indicate that the IL-10 gene may play a significant role in the etiology of schizophrenia among Han Chinese.

Possible association of the MAG locus with schizophrenia in a Chinese Han cohort of family trios

Neurotransmitter-based hypotheses have so far led to only moderate success in predicting new pathogenetic findings in etiology of schizophrenia. On the other hand, the more recent oligodendroglia hypotheses of this disorder have been supported by an increasing body of evidence. For example, the expression level of the myelin associated glycoprotein (MAG) gene has been shown to be significantly lower in schizophrenia patient groups compared to control groups. Such an effect might be a result of genetic variations of the MAG gene. In order to test this hypothesis, we genotyped four markers within the MAG locus in 413 trios sample of the Han Chinese using allele-specific PCR. None of the four markers revealed noticeable allelic significance. However, the four-marker and two-marker haplotypes covering components rs720309 and rs720308 were observed to be significantly associated with schizophrenia (P < 0.0001) in this study. In addition, we identified one common risk haplotype TA (rs720309-rs720308, present in 78.5% of the general population) that showed increased evidence of overtransmission from parents to affected offspring (P = 0.0001). The results demonstrated MAG might play a role in genetic susceptibility to schizophrenia. Furthermore, our finding of a possible association between the MAG locus and schizophrenia is in agreement with the hypotheses of oligodendrltic and myelination dysfunction.

A family-based and case-control association study of the NOTCH4 gene and schizophrenia

Recently a strong positive association between schizophrenia and Notch4 has been reported. Both individual markers and haplotypes showed association with the disease, with five markers (three microsatellites and two SNPs) being tested. In order to test this finding we genotyped these markers in the Han Chinese population using a sample of 544 cases and 621 controls as well as >300 trios. Analysis of allele, genotype and haplotype frequencies in both samples showed no association between the markers and the disease. Our results would indicate that a significant role for the Notch4 gene in schizophrenia can be ruled out in the Han Chinese. However, similar studies are necessary in the Caucasian population as linkage disequilibrium arrangements and founder effects may differ between these two populations.

102T/C polymorphism of serotonin receptor type 2A gene is not associated with schizophrenia in either Chinese or British populations

Several pieces of evidence implicate serotonin receptors in the aetiology of schizophrenia, and recently a number of studies have reported a genetic association between the 102T/C polymorphism of serotonin receptor type 2A gene and schizophrenia. Unfortunately a number of failures to replicate these positive associations in both Caucasian and Chinese populations have also been reported. We have examined the 102T/C polymorphism by PCR amplification and restriction analysis of DNA from: 202 schizophrenics and 202 controls from Shanghai; 112 schizophrenics and 224 parents from Chengdu, Cina; and 253 schizophrenics and 244 controls from the the UK. We find no evidence of association or transmission disequilibrium between the 102T/C polymorphism and schizophrenia in any of the groups we have examined. We conclude that either the original positive reports occurred by chance or any effect must be minimal, and urge caution in interpreting small positive results derived using data from different centres.

Lower CSF level of dynorphin(1-8) immunoreactivity in schizophrenic patients

Using a highly specific and sensitive radioimmunoassay for dynorphin(1-8) (D 1-8), and a singly blind test design, we measured D(1-8) immunoreactivity (ir D 1-8) in CSF of 35 first break cases of acute schizophrenic patients. All patients were free of psychotropic medication for at least one week before the study. Another 31 neurological patients suffered from cervical arthrosis, tumor, myelopathy etc. were studied as controls. The ir D(1-8) in CSF of schizophrenic patients were significantly lower than that of controls (91.8 +/- 5.6, means +/- S.E.M., and 131.9 +/- 6.8 fmol/ml CSF respectively, p less than 0.001).