Human clinical conditions causing hypergastrinemia include the hyperchlorhydric state caused by gastrinoma in Zollinger-Ellison syndrome (ZES), with or without MEN-1, and the hypochlorhydric states of chronic atrophic gastritis (CAG) due to autoimmune gastritis/pernicious anemia or Helicobacter pylori infection, vagotomy with gastric resection (some retained antrum), and prolonged proton pump inhibitor therapy. This evidence concerns the gene ATP4A and Zollinger-Ellison syndrome.