Aims/hypothesis  

Macrophage migration inhibitory factor (MIF) is a central mediator of innate immunity. Our aim was to investigate the triangular association between MIF genotypes, circulating MIF concentrations and incident type 2 diabetes, and to use a Mendelian randomisation approach to assess the causal role of MIF.

Methods  

Using a case–cohort design within the population-based MONICA/KORA Augsburg Study, based on 502 individuals with incident type 2 diabetes (293 men, 209 women) and 1,632 non-cases (859 men, 773 women), we determined MIF serum levels at baseline and genotyped four MIF single nucleotide polymorphisms (SNPs).

Results  

The C allele of SNP rs1007888 (3.8 kb 3′ of the translation termination codon) was associated with increased circulating MIF. MIF genotype rs1007888CC was associated with an increased risk of type 2 diabetes in women [hazard ratio (95% CI) 1.74 (1.02–2.97)], but not in men [1.17 (0.75–1.81)]. Elevated MIF serum levels were associated with higher type 2 diabetes risk also only in women [HR (95% CI) 1.95 (1.15–3.29) comparing extreme quartiles after multiple adjustment], but not in men (p for interaction 0.039). The association between MIF levels and incident type 2 diabetes was significantly higher in obese women (111 cases, 147 non-cases) compared with non-obese women (98 cases, 626 non-cases; p for BMI interaction 0.0002).

Conclusions/interpretation  

The consistent triangular relationship between genotypes, serum levels and incident type 2 diabetes in women indicates that MIF may play a causal role in the aetiology of type 2 diabetes and that elevated MIF levels confer a higher disease risk.