An increase in the concentration of the DPP4 substrates GLP-1, GIP (also called Gastric Inhibitory Polypeptide), the Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP) and oxyntomoduline has been related to gastrointestinal disorders [17,55]. The gene discussed is GCG; the disease is digestive system disorder.