Cytokines and hormones relevant to T2D can be classified into different clusters based on their site of production, including those produced by adipose tissue (such as adipsin, leptin, visfatin, and plasminogen activator inhibitor-1(PAI-1)), those produced by the gut (such as glucose-dependent insulinotropic peptide (GIP), glucagon-like peptide-1 (GLP-1), and ghrelin), and those produced by immune cells (such as resistin, interleukin 6 (IL-6), interleukin 10 (IL-10), and interleukin 1 receptor antagonist (IL-1RA)). This evidence concerns the gene LEP and type 2 diabetes mellitus.