GCG and obesity due to melanocortin 4 receptor deficiency: Obesity with normal glucose tolerance, in turn, is associated with an independent reduction of the incretin effect (~25%) (3), while herein, we describe that a lower threshold — 16% — for the incretin effect would be able to identify > 90% of subjects at risk for a 2-hour glucose level of ≥ 120 mg/dL.