GCK and type 2 diabetes mellitus: Genome-wide association studies (GWAS) identified several genes such as the glucokinase (GCK), the glucokinase regulator (GCKR), the transcription factor 7-like 2 (TCF7L2), the hepatocyte nuclear factor-1A (HNF1A), and fat mass and obesity-associated (FTO) gene playing a role in developing T2DM [13].