The multiple endocrine neoplasia (MEN) syndromes are three related disorders affecting the thyroid and other hormone producing (endocrine) glands of the body.

The three forms of MEN are MEN1 (Wermer's syndrome), MEN2A (Sipple syndrome), and MEN2B (previously known as MEN3). Each is a genetic condition that predisposes the carrier of the gene to excessive growth of cells (hyperplasia) and tumor formation in a number of endocrine glands.

MEN1 patients experience hyperplasia or tumors of several endocrine glands, including the parathyroids, the pancreas, and the pituitary. The most frequent symptom of MEN1 is overgrowth of the parathyroid glands. This leads to an excess secretion of parathyroid hormone causing elevated blood calcium levels, kidney stones, weakened bones, and nervous system depression. Almost all MEN1 patients show these symptoms by age 40.

Tumors of the pancreas are also common in MEN1. Excessive secretion of...