MEN1 and neuroendocrine neoplasm: Mutations in MEN1 gene are responsible for the onset of multiple endocrine neoplasia type 1 (MEN1), a rare autosomal dominant disorder characterized by endocrine alterations that must be present in a combined manner for at least two of the following conditions: tumors of the parathyroid glands, anterior pituitary gland, and neuroendocrine tumors of the gastro-entero-pancreatic tract (GEP-NET).