GCG and diabetes mellitus: Examples of typical functional pNET clinical syndromes include excess insulin (insulinoma) leading to recurrent hypoglycemic episodes, gastrin excess (gastrinoma) giving rise to Zollinger-Ellison syndrome, glucagon excess (glucagonoma) leading to diabetes, diarrhea, necrolytic erythema migrans and venous thrombosis, vasoactive intestinal peptide (VIPoma) leading to diarrhea, achlorhydria and hypokalemia (Verner–Morrison syndrome) somatostatin (somatostatinoma) leading to diabetes, diarrhea and gallstones, or pancreatic polypeptide (PPoma) leading to diarrhea.