TCF7L2 and type 2 diabetes mellitus: The latter is also the case of the rs7903146 (C/T), located in the intron 4 of the transcription factor 7-like 2 (TCF7L2) gene, which is also the common variant with the strongest association with T2D and with an odds ratio (OR) of 1.35 (T vs. C, 95%CI = 1.31–1.39) [48,49,50].