FTO and obesity due to melanocortin 4 receptor deficiency: Although many genetic variants have been repeatedly associated with obesity, such as those located within FTO or MC4R genes (Frayling et al., 2007; Loos et al., 2008; Rouskas et al., 2012), their ability to stratify obesity remains insufficient, as compared to traditional risk factors or familial resemblance (Loos and Janssens, 2017).