For example, Melanocortin-4 Receptor (MC4R) is a GPCR involved in food consumption and mutations in this receptor are the most common cause of monogenic obesity (Vaisse et al., 1998; Vaisse et al., 2000; Lubrano-Berthelier et al., 2006). Here, MC4R is linked to obesity due to melanocortin 4 receptor deficiency.