Vice versa, severe hypersecretion of gastrin as seen in the Zollinger–Ellison syndrome caused by gastrin-producing tumors (gastrinomas) is, in its fulminant forms, also life-threatening—partly due to gross gastric hyperacidity with multiple duodenal and jejunal peptic ulcers, diarrhea and severe water–electrolyte disturbances and partly because gastrinomas—although mostly slow-growing—are malignant, metastatic neoplasias [7,8]. Here, GAST is linked to peptic ulcer disease.