Several mechanisms have been proposed to explain the link between sleep deprivation and obesity, including hormonal imbalances, particularly involving leptin and ghrelin [138], overactivation of the HPA axis resulting in increased cortisol secretion [132,139], elevated levels of pro-inflammatory cytokines, and unfavorable lifestyle changes that promote a positive energy balance. The gene discussed is LEP; the disease is obesity due to melanocortin 4 receptor deficiency.