LEP and obesity due to melanocortin 4 receptor deficiency: Investigations into rare forms of obesity such as Bardet-Biedl syndrome (BBS); leptin, leptin receptor (LEPR), or proopiomelanocortin (POMC) receptor deficiencies; and acquired hypothalamic obesity have advanced our understanding of the biology of hyperphagia and its distinction from other overeating behaviors [2, 4, 6–11].