TCF7L2 and obesity due to melanocortin 4 receptor deficiency: Besides the FTO, Melanocortin 4 Receptor (MC4R) and Transcription Factor 7-Like 2 (TCF7L2) genes are the two commonly studied candidate genes for obesity and T2D [24,25,26,27,28,29,30,31,32,33,34,35,36,37,38].