Once in a lifetime: Continuing our series on conditions that GPs may only encounter once in a career, gastroenterology resident doctors Dr Kevin Jacob, Dr Sana Mallick, Dr Belinda Eze and consultant gastroenterologist Dr Andrew Poullis provide an overview of the rare disorder known as Zollinger-Ellison syndrome (ZES) What is Zollinger-Ellison syndrome? Zollinger-Ellison syndrome (ZES)