Additionally, the melanocortin accessory protein MRAP2 has been shown to modulate trafficking and function of MC4R (Sebag et al., 2013) to a level that is physiologically significant, as transgenic mice with whole-body deletion and brain-specific deletion of Mrap2 develop severe obesity at a young age (Asai et al., 2013). Here, MRAP2 is linked to obesity due to melanocortin 4 receptor deficiency.