Association study of MIF promoter polymorphisms with suicide completers in the Japanese population

Numerous studies suggest that inflammation plays a key role in suicidal behavior. Macrophage migration inhibitory factor (MIF), a proinflammatory cytokine, has received increasing attention in depression research. However, no study has investigated whether MIF has genetic involvement in completed suicide. In this study, we sought to explore the relationship between two functional polymorphisms on the MIF gene promoter (MIF-794CATT_5-8 microsatellite and MIF-173G/C single-nucleotide polymorphism [SNP]) and completed suicide by using one of the largest samples of suicide completers ever reported.

The subjects comprised 602 suicide completers and 728 healthy controls. We genotyped MIF-794CATT_5-8 microsatellite by polymerase chain reaction-based size discrimination assay and MIF-173G/C SNP by TaqMan^® SNP genotyping assay. The allele-, genotype-, or haplotype-based association analyses between the suicide completers and the controls were carried out with the χ² test, the Cochran-Armitage trend test, or Fisher's exact test.

Analyses of allele or genotype frequency distributions of the polymorphisms studied here did not reveal any significant differences between the suicide completers and the controls. Haplotype analysis also revealed no association with completed suicide.

To our knowledge, this is the first study that has examined the genetic association between MIF and completed suicide. Our results suggest that the effects of MIF-794CATT_5-8 microsatellite and MIF-173G/C SNP on the MIF gene promoter might not contribute to the genetic risk of completed suicide in the Japanese population.