TCF7L2 and type 2 diabetes mellitus: For example, the fetal risk allele at TCF7L2, which has a relatively large effect on type 2 diabetes risk, has no effect on birthweight, and the fetal risk allele at the ANK1 locus is associated with a higher birthweight [59] despite its role in regulating NKX6-3 [61], a vital transcription factor involved in pancreatic beta cell development [62].