As a matter of fact, most of the T2D susceptibility genes identified in the pre-GWAS era are key players in the development of some forms of monogenic diabetes; KCNJ11, HNF4A, SLC2A2, PPARG, and INSR. Recent studies identified few other monogenic diabetes loci like HNF1A, HNF1B, GCK, PDX1, GLIS3, WFS1, PAX4, and LMNA which harbor variants associated with T2D risk (Sidransky, 2006; Sandhu et al., 2007; Wegner et al., 2007; Voight et al., 2010; Rees et al., 2011; Cho et al., 2012). The gene discussed is GCK; the disease is diabetes mellitus.