Common quantitative trait locus downstream of RETN gene identified by genome-wide association study is associated with risk of type 2 diabetes mellitus in Han Chinese: A Mendelian randomization effect

Objective: Plasma resistin level is a potential molecular link between obesity and diabetes. Causal role of resistin, type 2 diabetes mellitus (T2DM) and genetic variants have not been thoroughly investigated. Therefore, we conducted a genome-wide association study (GWAS) to identify quantitative trait loci associated with resistin levels and investigated whether these variants were prospectively associated with the development of metabolic syndrome (MetS) and T2DM in an independent community-based cohort, the CardioVascular Disease risk FACtors Two-township Study (CVDFACTS). Research Design and Methods: We genotyped 382 young-onset hypertensive (YOH) subjects with Illumina HumanHap550 chips and searched for quantitative trait loci (QTLs) of resistin in the 1^st stage GWAS and confirmed the finding in another 559 YOH subjects. Logistic regression was used to examine the Mendelian randomization effects between genotypes of confirmed QTLs and metabolic outcomes in 3400 subjects of CVDFACTS. Results: Two single nucleotide polymorphisms (SNP) (rs3745367 and rs1423096) were significantly associated with resistin levels (p=5.52×10^-15 and p=2.54×10^-20) and replicated in another 559 YOH subjects (p=1.29×10^-3 and p=1.13×10^-7), respectively. The SNP rs1423096 was further associated with the levels of HDL-C (p=0.006), the risk of MetS (OR=2.21, p=0.0034) and T2DM (OR=1.62, p=0.0063) in the CVDFACTS. People with the haplotypes A-G and G-G determined by rs3745367 and rs1423096 showed a significantly increased T2DM risk (p=0.0068 and p=0.0035, respectively) compared with those with A-A haplotype. Conclusion: We have found that rs3745367 and rs1423096 on the RETN gene were significantly associated with resistin levels. However, rs1423096, downstream of RETN, seems to be associated with MetS and T2DM risk more so than rs3745367. The established genotype-disease association points to a causal association of resistin and T2DM.