TCF7L2 and type 2 diabetes mellitus: These included two clusters of 3 index SNPs, each associated with 25(OH)D concentrations (GC rs2282679, DHCR7 rs12785878, CYP2R1 rs12794714), and T2D (IGF2BP2 rs1470579, TCF7L2 rs7903146, and KCNQ1 rs2237896), respectively.