Enrichment of MC4R in cilia requires its interaction partner, the single pass membrane protein melanocortin receptor accessory protein 2 (MRAP2) [13] and deletion of MRAP2 or mutations that block ciliary targeting of MC4R result in profound obesity in human patients and in mice [13–20]. This evidence concerns the gene MRAP2 and obesity due to melanocortin 4 receptor deficiency.