Familial multiple endocrine neoplasia type 1 (FMEN1) is an inherited disorder that affects the endocrine glands. Normally, the hormones released by endocrine glands are carefully balanced to meet the body's needs. In patients with FMEN1, sometimes more than one group of endocrine glands, such as the parathyroid, the pancreas, and the pituitary become overactive at the same time. Most people who develop overactivity of only one endocrine gland do not have FMEN1. FMEN1 is quite rare, occurring in about 3 to 20 persons out of 100,000. It affects both sexes equally and shows no geographical, racial, or ethnic preferences.