Reduced plasma GLP-1 concentrations were sometimes observed in T2DM [23–25] even prediabetes [26] stages, which may provide an explanation to the markedly impaired incretin effect in patients with T2DM [27] in addition to the deficient in the β-cell response to GLP-1 after meal ingestion [20]. The gene discussed is GCG; the disease is type 2 diabetes mellitus.