It has long fascinated investigators/clinicians because of its multiple causes including diseases such as pancreatic neuroendocrine tumors (panNET) and other neuroendocrine tumors (NETs) causing fasting gastrin levels >100-fold increased, associated with such florid acid hypersecretion that if untreated (i.e., ZES), it frequently leads to a fatal outcome [24,28,29,42]. The gene discussed is GAST; the disease is Zollinger-Ellison syndrome.