Indeed, the “hunger hormone” ghrelin was first described as a growth hormone secretagogue, but its key role in the regulation of appetite, food intake, adiposity and metabolism have directed the main therapeutic focus of ghrelin and its receptor towards obesity research with promising anti-obesity potential [41,45,76,[89], [90], [91], [92]]. The gene discussed is GHRL; the disease is obesity due to melanocortin 4 receptor deficiency.