LEP and obesity due to melanocortin 4 receptor deficiency: Among the large set of genes influencing obesity, those in the leptin-melanocortin satiety signaling pathway are the most determinant known to date, with homozygous mutations in some causing early onset severe obesity with hyperphagia (Jackson et al., 1997; Chiurazzi et al., 2020; Trang and Grant, 2023).