MEN1 and multiple endocrine neoplasia type 1: Multiple endocrine neoplasia type 1 (MEN1) is a rare autosomal dominant disorder arising from mutations of the MEN1 tumor suppressor gene on chromosome 11q13; MEN1 is characterized by the development of neuroendocrine tumors, including those of the parathyroid, gastrointestinal endocrine tissue and anterior pituitary.