The largest study dealing with only sporadic ZES patients was an NIH study [25] included 106 patients (90 active, 16 cured) in which all patients with active disease had chronic hypergastrinemia and the disease was long-standing with mean duration of ZES since onset at the time of the study of 13 years and a median fasting gastrin level 4-fold elevated. This evidence concerns the gene GAST and Zollinger-Ellison syndrome.