ZES/MEN1 patients differ from patients with sporadic ZES in a number of features related both to the gastrinoma itself and also to the presence of other NETs/other tumors in other organs which in some cases can cause functional syndromes, such as hyperparathyroidism, which can affect the management of the ZES [35,251,281,313,314,315]. The gene discussed is MEN1; the disease is Zollinger-Ellison syndrome.