The melanocortins, alpha-, beta- and gamma-melanocyte-stimulating hormones (MSHs) and adrenocorticotropin (ACTH), are peptides derived from a precursor protein POMC. The MSH peptides and ACTH bind to a family of five Class 1 Gs -coupled seven transmembrane receptors (MC1-5) and play important roles in energy balance, reproductive function, pigmentation and inflammation. MC2, the ACTH receptor, is a member of this family but is the only one that does not bind the MSHs, it instead binds ACTH exclusively. MC2 is expressed mainly in cells of the adrenal cortex, where it signals cells in the adrenal cortex to synthesize and secrete glucocorticoids. Mutations in MC2 lead to familial glucocorticoid deficiency, or ACTH insensitivity. Familial glucocorticoid deficiency can lead to increased pigmentation and increased longitudinal bone growth. In addition to mutations in MC2 leading to Familial glucocorticod deficiency, it has also been shown that mutations in MRAP also lead to this disorder. Expression of MC2 on the cell surface has been found to be dependent on the interaction of MC2 with a protein called MC2-R accessory protein (MRAP). This interaction helps to move MC2 from the endoplasmic reticulum to the cell surface.