The most accurate predictor of the target AUC for all weight categories was cystatin C (MPE%: +0.2%, −2.0%, and −0.1% for patients with a normal weight, those who were overweight, and those who had obesity, respectively) with low imprecision (MAPE%: 9.8%, 9.5%, and 13.3%, respectively). The gene discussed is CST3; the disease is obesity due to melanocortin 4 receptor deficiency.