GCG and obesity due to melanocortin 4 receptor deficiency: Several mechanisms may be responsible for insulin resistance at this stage of progression: increased growth hormone secretion in mid-childhood and during adolescence (92-94), increased glucagon secretion due to intra-islet insulin deficiency (see “Glucagon, Islet Amyloid Polypeptide” and “Evidence for Insulin Resistance Preceding Autoimmunity”), infections (95), and/or obesity (see “Obesity”).