Lifestyle intervention modifies the effect of the MC4R genotype on changes in insulin resistance among women with prior gestational diabetes: Tianjin Gestational Diabetes Mellitus Prevention Program

BACKGROUND: A history of gestational diabetes mellitus (GDM) has been related to an elevated risk of type 2 diabetes. The melanocortin-4 receptor (MC4R) genotype has been related to glycemic changes in women with prior GDM. OBJECTIVE: The objective of this study was to analyze whether lifestyle intervention modified the association between the MC4R genotype and changes in insulin sensitivity among women with prior GDM. METHODS: We genotyped MC4R rs6567160 and measured glucose and insulin in fasting plasma samples at baseline and during the first 2 follow-up visits in 1128 women with prior GDM. They were randomly assigned to either a 4-y lifestyle intervention involving both diet and physical activity or a control group from a randomized clinical trial, the Tianjin Gestational Diabetes Mellitus Prevention Program. We analyzed the interaction between the MC4R genotype and lifestyle intervention on changes in insulin resistance. RESULTS: From baseline to 1.28 y, the MC4R genotype was related to changes in fasting insulin, HOMA-IR, and homeostasis model assessment of β cell function (HOMA-B) in the intervention group. Each risk allele (C) of rs6567160 was associated with a 0.08-unit greater decrease in log(insulin), log(HOMA-IR), and log(HOMA-B) (P = 0.02, 0.04, and 0.04, respectively), whereas in the control group, each C allele tended to be associated with a greater increase in HOMA-IR (P = 0.09). We found significant interactions between the MC4R genotype and lifestyle intervention on 1.28-y changes in fasting insulin and HOMA-IR (P = 0.006 and 0.008, respectively), and such interaction remained significant when we analyzed the trajectory of changes in insulin and HOMA-IR from baseline to 2.55 y (both P = 0.03). CONCLUSIONS: The exploratory results from the first 2 follow-up visits indicate that women with prior GDM carrying a diabetes-increasing MC4R genotype (CC or TC) may obtain better improvement than the TT genotype in insulin resistance through lifestyle intervention. This trial was registered at clinicaltrials.gov as NCT01554358.