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What is MEN1?

Multiple endocrine neoplasia type 1 (MEN1) is an inherited disorder that affects the endocrine glands. MEN1 is quite rare, occurring in about 3 to 20 persons out of 100,000. It affects both sexes equally and shows no special geographical, racial, or ethnic preferences. MEN1 is a genetic syndrome, and the genetic cause has been identified as one of a number of mutations in the MENIN gene.

Endocrine glands are different from other organs in the body because they release hormones into the bloodstream. Hormones are powerful chemicals that travel through the blood, controlling and instructing the functions of various organs. Normally, the hormones released by endocrine glands are carefully balanced to meet the body's needs.

MEN1 consists of tumors involvinig the pituitary, parathyroid and pancreas glands. MEN1 is quite rare, however, and the vast majority of people who develop pituitary tumors do not have MEN1. If you and a family member both have pituitary tumors or you have been diagnosed with hyperparathyoidism in addition to a pituitary tumor, genetic testing for MEN1 may be indicated. In the absence of one of these risk factors, MEN1 is extremely unlikely.

How Does MEN1 Affect the Endocrine Glands?

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The Parathyroid Glands

The parathyroids are the endocrine glands most often affected by MEN1. The human body normally has four parathyroid glands, which are located close to the thyroid gland in the front of the neck. The parathyroids release a chemical called parathyroid hormone, which helps maintain a normal supply of calcium in the blood, bones, and urine.

In MEN1 all four parathyroid glands tend to be overactive. Overactive parathyroid glands secrete too much parathyroid hormone, leading to excess calcium in the blood. High blood calcium, known as hypercalcemia, can exist for many years before it is found by accident or by family screening. Unrecognized hypercalcemia can cause excess calcium to spill into the urine, leading to kidney stones or kidney damage.

Nearly everyone who inherits a susceptibility to MEN1 will develop parathyroid overactivity (hyperparathyroidism) by age 60. Hyperparathyroidism can cause problems such as tiredness, weakness, muscle or bone pain, constipation, indigestion, kidney stones, or thinning of bones.

Treatment of Hyperparathyroidism. It is sometimes difficult to decide whether hyperparathyroidism in MEN1 is severe enough to need treatment, especially in a person who has no symptoms. The usual treatment is an operation to remove the three largest parathyroid glands and all but a small part of the fourth. After parathyroid surgery, regular testing should continue, since the small piece of parathyroid tissue can grow back and cause recurrent hyperparathyroidism. People whose parathyroid glands have been completely removed by surgery must take daily supplements of calcium and vitamin D to prevent hypocalcemia (low blood calcium).

The Pancreas

The pancreas, located behind the stomach, releases digestive juices into the intestines and secretes key hormones into the bloodstream. Some hormones produced in the islet cells of the pancreas and their effects are listed below:

  • gastrin -- increases stomach acid;
  • insulin -- lowers blood sugar;
  • glucagon -- raises blood sugar;
  • vasoactive intestinal peptide (VIP) -stimulates many cells;
  • somatostatin -- inhibits many cells.

A common problem in MEN1 is the tendency of the pancreas to develop one or more islet cell tumors that produce high amounts of gastrin. Gastrin is a hormone that normally circulates in the blood, causing the stomach to secrete enough acid needed for digestion. If exposed to too much gastrin, the stomach releases excess acid, which leads to the formation of severe stomach ulcers. Too much gastrin can also cause serious diarrhea. Among persons with MEN1 who have overactive glands, about one in three has gastrin-releasing pancreatic tumors, called gastrinomas. (The illness associated with these tumors is sometimes called Zollinger-Ellison syndrome.) The ulcers caused by gastrinomas are much more dangerous than typical stomach or intestinal ulcers; left untreated, they can cause rupture of the stomach or intestine and even death.

Pituitary Tumors

The pituitary gland becomes overactive in about one of six persons with MEN1. Pituitary tumors and their treatment are covered extensively elsewhere on this website.



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Can MEN1 Be Cured?

There is no cure for MEN1 itself, but most of the health problems caused by MEN1 can be recognized at an early stage and controlled or treated before they become serious problems.

If you have been diagnosed with MENl, it is important to get periodic checkups because MEN1 can affect different glands and, even after treatment, residual tissue can grow back. Careful monitoring enables your doctor to adjust your treatment as needed and to check for any new disturbances caused by MEN1.

MEN1 Detection

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Is MEN1 the Same in Everyone?

Although MEN1 tends to follow certain patterns as described earlier, there is considerable variation in the ways MEN1 can affect a person's health. Not only do the features of MEN1 vary among members of the same family, but some families with MEN1 tend to have a higher rate of prolactin-secreting pituitary tumors and a much lower frequency of gastrin-secreting pancreatic tumors.

In addition, the age at which MEN1 can begin to cause endocrine gland over-function can differ strikingly from one family member to another. One member may have only mild hyperparathyroidism beginning at age 50, while another may develop complications from tumors of the parathyroid, pancreas, and pituitary by age 20.

How Is MEN1 Detected?

Genetic testing that detects the abnormalities in the MEN1 gene that causes the MEN1 syndrome is available. Most, but not all, mutations can be detected by commercially available genetic testing.

Why Screen for MEN1?

MEN1 is not an infectious or contagious disease, nor is it caused by environmental factors. MEN1 is a genetic disorder that can only be inherited from one parent. Because MEN1's transmission pattern is so well understood, family members at high risk for the disorder can be easily identified. For this reason, screening can yield important information for people at high risk of inheriting MEN1.

Testing is also useful because it can detect the blood chemical problems caused by MEN1 many years before major complications develop. Finding these hormonal imbalances early enables your doctor to begin preventive treatment, reducing the chances that MEN1 will cause problems later.

Who Should Be Screened for MEN1?

Each of us has millions of genes in each of our cells, which determine how our cells and bodies function. In people with MEN1, there is a mutation, or mistake, in one gene. A carrier is a person who has the MEN1 gene. The MEN1 gene is transmitted directly to a child from a parent carrying the gene. The chances that any child of an MEN1 "carrier" will inherit this disorder are 50-50.

The persons who should be screened are the first-degree relatives (parents, brothers, sisters, and children) of persons with MEN1, since these family members are at 50-50 risk of already having inherited the MEN1 gene. Though the abnormal gene is present before birth, it tends to become evident at varying ages and in different organs. A "silent" carrier has the gene but has not yet shown any hormonal disturbance caused by the gene. Periodic testing may also be considered in people whose nearest affected relative is a grandparent, uncle, or aunt (that is, a second-degree relative), if there is reason to believe that the parent may be a silent MEN1 gene-carrier. Genetic screening for MEN1 should also be considered in patients who have pituitary tumors and hyperparathyroidism.


Research & Information

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Research in MEN1

We encourage you to contact your Neuroendocrine and Pituitary Clinical Center physician if you are interested in research in this area.

This epub was written by Stephen J. Marx, M.D., of the National Institute of Diabetes andDigestive and Kidney Diseases. It is based in part on the booklet UrLderstandireg Multiple EndocrirLeNeoplasia Type 1, published by the NIH ClinicalCenter's Communications Office.

This epub is not copyrighted. Readers are encouraged to duplicate and distribute as many copies as needed. Printed single copies may be obtained from NlDDK's Office of Health Research Reports at the address given under "Other Resources" in this fact sheet.

NIH Publication No. 89-3048 April 1989

Updated by BS and KKM 2/4/15