The reasons for the inconsistent results observed are still unclear; however, several factors have been postulated, which include the different diagnostic criteria used to diagnose T2DM and pre-DM, smaller sample size, timing of GLP-1 measurements, glucose challenge used (OGTT or mixed meals), GLP-1 detection method, racial and genetic differences (18, 19, 26, 28, 29). This evidence concerns the gene GCG and diabetes mellitus.