C3 and obesity due to melanocortin 4 receptor deficiency: To assess whether C3, ZAG and α2-MG could serve as accurate diagnostic biomarkers of T2DM, we performed ROC curve analysis to evaluate their positive and negative predictive values for obesity and T2DM+obesity development, with the prediction thresholds determined using the maximum Youden's index cut-off point (Figures 2, 3).