FTO and obesity due to melanocortin 4 receptor deficiency: Our in-depth analysis reveals that FTO co-expresses with MGRN138 which in turn shares a physical interaction with MC4R, and it has been shown that MGRN1 inhibits MC4R signalling by displacement of Galpha(s), accounting for coat colour and obesity, features of the mahoganoid phenotype in mouse, and plays a key role in insulin sensitivity39–42.