MTOR and obesity due to melanocortin 4 receptor deficiency: Previous experimental studies by our research group found that the promoter region of the tuberous sclerosis complex 1 (Tsc1) gene in rat hypothalamus had an obesity-related methylation site; the obesity rat Tsc1 promoter appeared to be at a high methylation state and its downstream mammalian target of rapamycin (mTOR) gene expression was upregulated, which may be attributed to a weakened inhibitory effect on the mTOR gene as a result of an increased methylation of the Tsc1 promoter, thereby increasing appetite and food intake and finally causing obesity [9].