Zollinger–Ellison syndrome (ZES) is a clinical manifestation associated with an underlying gastrinoma of the duodenum or pancreas, a neuroendocrine neoplasm (NEN) that can cause hypersecretion of gastric acid, typically leading to gastroesophageal reflux disease (GERD), recurrent peptic ulcers and chronic diarrhea due to hypersecretion of gastrin. This evidence concerns the gene GAST and gastroesophageal reflux disease.