This review analyses current data on the common pathogenic pathways between T2DM and PD and describes: (a) the role of glucagon-like peptide-1 (GLP-1) and GLP-1 receptors, (b) the development of GLP-1 receptor agonists and (c) the current data regarding the role of these new drugs as disease-modifying agents based on data from studies on animal models and preclinical as well as clinical studies. The gene discussed is GCG; the disease is type 2 diabetes mellitus.