MC4R and obesity due to melanocortin 4 receptor deficiency: In this system, α-MSH, which is derived from POMC over ACTH, and one of its receptors, the melanocortin 4 receptor (MCR4) (17), seem to play a central role: defects or inhibition of MCR4 have been associated with a higher risk for obesity (18) and both ACTH and MCR4 are known to play a critical role in stress-induced pathologies and associated metabolic side effects.