TCF7L2 and type 2 diabetes mellitus: Additionally, polymorphisms located in introns in the genomic region that codes for human tcf7l2 exon 3a (Figure 1 C, D), segregate with acquisition of type-2 diabetes (Grant et al., 2006), and conditional knockdowns of tcf7l2 give rise to mice with phenotypes comparable to diabetic patients (Boj et al., 2012; Duncan et al., 2019).