This model is supported by the fact that leptin stimulates the expression of SOCS-3, a protein that directly inhibits leptin signaling[15], [16], [17], and that ablation of SOCS-3 in neurons enhances leptin sensitivity and protects against diet-induced obesity[18], [19], [20]. This evidence concerns the gene SOCS3 and obesity due to melanocortin 4 receptor deficiency.