IGF1 and obesity due to melanocortin 4 receptor deficiency: Although we are not aware of any prior analyses of IGF-1 levels in youth-onset T2D, lower IGF-1 levels have been reported previously in youths with obesity (compared with youths with normal weight) and in adults with obesity and diabetes.19,20 However, whether a lower IGF-1 level is the cause or result of obesity and diabetes is unclear.