AKT1 and obesity due to melanocortin 4 receptor deficiency: For example, in experimental murine studies of obesity-related insulin resistance, an increased loss of muscle mass occurs via insulin receptor substrate-1/phosphatidylinositol-3-kinase Akt pathway down-regulation47; since adiponectin inhibits the muscle degradation that occurs via this pathway48, the decreased adiponectin concentrations that arise in individuals with obesity might be contributory.