MC4R and type 2 diabetes mellitus: MC4R-rs663129 induced a significantly higher susceptibility to T2DM among individuals who were nonsmokers in the codominant (OR = 1.64, 95% CI = 1.07–2.52, p = 0.023), dominant (OR = 1.60, 95% CI = 1.07–2.40, p = 0.023) and additive (OR = 1.40, 95% CI = 1.00–1.95, p = 0.049) models.