A study performed on the secretion of GLP-1 in patients with T2DM found that the patients generally did not have a reduced secretion of GLP-1 in response to oral glucose or liquid meal tests; however, they had significantly low glycemic control responses, meaning that the effectiveness of the GLP-1 that was being secreted was definitely compromised [39]. This evidence concerns the gene GCG and type 2 diabetes mellitus.