FTO is the first human obese gene identified, while subsequent research has shown that resistance to obesity does not come from FTO. Smemo et al. [66] first revealed that FTO regulates the expression of the IRX3 gene, and the classic obesity risk site rs9930506 of FTO does not change the mRNA level of the FTO gene in brain tissues, but is associated with changes in IRX3 expression. Here, FTO is linked to obesity due to melanocortin 4 receptor deficiency.