To explore the association between DRD4 polymorphisms and schizophrenia risk, a meta-analysis was carried out with 41 case–control articles. Specifically, we included 28 articles (5,735 cases and 5,278 controls) that pertained to the 48 bp variable number tandem repeat (VNTR) polymorphism, nine articles (1,517 cases and 1,746 controls) that corresponded to the 12 bp tandem repeat (TR), six articles (1,912 cases and 1,836 controls) that addressed the 120 bp TR, 10 articles (2,927 cases and 2,938 controls) that entailed the −521 C>T polymorphism, six articles (1,735 cases and 1,724 controls) that pertained to the −616 C>G polymorphism, and four articles (1,191 cases and 1,215 controls) that involved the −376 C>T polymorphism. Pooled analysis, subgroup analysis, and sensitivity analysis were performed, and the data were visualized by means of forest and funnel plots. Results of pooled analysis indicated that the −521 CC variant (Pz=0.009, odds ratio [OR] =1.218, 95% confidence interval [CI] =1.050–1.413) and genotype L/L (ie, long allele) of the 120 bp TR were risk factors of schizophrenia (Pz=0.004, OR =1.275, 95% CI =1.081–1.504). The 48 bp VNTR, the 12 bp TR, the −616 C>G polymorphism, and the −376 C>T polymorphism were not associated with schizophrenia. Additional research is warranted to explore the association between polymorphisms of DRD4 and schizophrenia risk.

Background: In order to explore the association between the SLC6A4 gene and the risk of schizophrenia, an updated meta-analysis was conducted using a total of 46 scientific articles. Methods: Through a literature search, papers studied included 35 articles on serotonin-transporter-linked polymorphic region (5-HTTLPR) with 8,752 cases and 10,610 controls, 17 articles on second intron variable number of tandem repeats with 7,284 cases and 8,544 controls, four studies on rs1042173 with 1,351 cases and 2,101 controls, and four studies on rs140700 with 1,770 cases and 2,386 controls. Pooled, subgroup, and sensitivity analyses were performed, and the results were visualized by forest and funnel plots. Results: An association between 5-HTTLPR and the risk of schizophrenia was not found, except for an Indian subgroup analysis (P z =0.014, OR =1.749, 95% CI =1.120-2.731). A 10 repeats/12 repeats (10R/12R) genotype was a protective factor against schizophrenia (P z =0.020, OR =0.789, 95% CI =0.646-0.963), but a 12R/12R genotype was a risk factor for schizophrenia (P z =0.004, OR =1.936, 95% CI =1.238-3.029) in the pooled analyses. In Caucasians, a GG genotype of rs1042173 may be a risk factor for schizophrenia (P z =0.006, OR =1.299, 95% CI =1.079-1.565). No association was found between rs140700 and the risk for schizophrenia. Conclusion: Through meta-analysis, we were able to gain insight into previously reported associations between SLC6A4 polymorphism and schizophrenia.

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To determine whether mitochondrial DNA (mtDNA) variations are associated with schizophrenia, 313 patients with schizophrenia and 326 unaffected participants of the northern Chinese Han population were included in a prospective study. Single-nucleotide polymorphisms (SNPs) including C5178A, A10398G, G13708A, and C13928G were analyzed by polymerase chain reaction–restriction fragment length polymorphism (PCR–RFLP). Hypervariable regions I and II (HVSI and HVSII) were analyzed by sequencing. The results showed that the 4 SNPs and 11 haplotypes, composed of the 4 SNPs, did not differ significantly between patient and control groups. No significant association between haplogroups and the risk of schizophrenia was ascertained after Bonferroni correction. Drawing a conclusion, there was no evidence of an association between mtDNA (the 4 SNPs and the control region) and schizophrenia in the northern Chinese Han population.