In general, obesity is associated with dysfunction of the hypothalamic–pituitary–adrenal (HPA) axis with a reduced response to cortisol feedback with the immune system (chronic low-grade inflammation) and dysregulation of metabolic pathways (leptin, insulin, NPY, and ghrelin, among others) [46]. The gene discussed is LEP; the disease is obesity due to melanocortin 4 receptor deficiency.