LEP and obesity due to melanocortin 4 receptor deficiency: The close correlation of OBRe and leptin levels in energy homeostasis has been demonstrated in several clinical studies: OBRe level is inversely correlated with obesity and leptin levels [19], [20], [21]; OBRe expression is increased in response to weight loss, fasting and food restriction [21], [22]; and a higher proportion of OBRe-bound leptin is present in circulation in the lean than the obese individuals [21], [23].