Administration of leptin completely recovers the obesity phenotype of ob/ob mice and induces anorexia and body weight loss in normal mice, suggesting that leptin negatively regulates feeding behaviors and inhibits obesity (Halaas et al., 1995; Pelleymounter et al., 1995; Rentsch et al., 1995; Weigle et al., 1995). Here, LEP is linked to obesity due to melanocortin 4 receptor deficiency.