TCF7L2 and type 2 diabetes mellitus: In 2007, five independent groups performed genome-wide association studies (GWAS) for type 2 diabetes using populations of European descent; they identified TCF7L2, which had previously been discovered via positional cloning in 2006 [3], as well as eight other genetic loci that affect susceptibility to type 2 diabetes, namely SLC30A8, HHEX, CDKN2A/B, CDKAL1, IGF2BP2, KCNJ11, PPARG, and FTO [4–8].