A literature search was performed screening PubMed database using combinations of the following search terms: “DM”; “type 1 diabetes”; “type 2 diabetes”; “bone metabolism”; “incretin hormones”; “GLP-1”; “incretin-based therapy”; “DPP-4 inhibitors.” This initial screening identified a total of 2492 records. Here, GCG is linked to type 2 diabetes mellitus.