FTO and obesity due to melanocortin 4 receptor deficiency: Among the m6A regulators, FTO was the first m6A demethylase that was discovered in 2011 (Jia et al., 2011), which has attracted much interest because of its involvement in obesity and obesity-induced metabolic diseases (Zhao et al., 2014) and the occurrence, development, and prognosis of many kinds of cancer, such as melanoma (Yang et al., 2019), acute myeloid leukemia (AML; Li Z. et al., 2017), glioblastoma (Cui et al., 2017), lung carcinoma (Li et al., 2019a), hepatocellular carcinoma (Li et al., 2019b), and BC (Niu et al., 2019).