Definition of Multiple endocrine neoplasia (MEN) II:

Multiple endocrine neoplasia, type II (MEN II) is an inherited disorder in which one or more of the endocrine glands are overactive or form a tumor. Endocrine glands most commonly involved include:

• Adrenal (about half the time)
• Parathyroid (20% of the time)
• Thyroid (almost all of the time)

See also: MEN I

Causes, incidence, and risk factors:

The cause of MEN II is a defect in a gene called RET. This defect causes many tumors to appear in the same person, but not necessarily at the same time. The adrenal tumor is called a pheochromocytoma, and the thyroid tumor is a medullary carcinoma of the thyroid.

The tumors involve multiple parts of the thyroid gland or more than one of the parathyroid and adrenal glands. Tumors in the thyroid, adrenal, or parathyroid glands may occur years apart.

The disorder may occur at any age, and affects men and women equally. The main risk factor is a family history of MEN II.

There are two subtypes of MEN II -- MEN IIa and IIb. MEN IIb is less common.