Below is an instruction from Human. Write a response.
    ### Instruction:
    What causes Zollinger-Ellison Syndrome ?
    ### Response:
    Experts do not know the exact cause of Zollinger-Ellison syndrome. About 25 to 30 percent of gastrinomas are caused by an inherited genetic disorder called multiple endocrine neoplasia type 1 (MEN1).1 MEN1 causes hormone-releasing tumors in the endocrine glands and the duodenum.
    