Multiple Endocrine Neoplasia (MEN) Syndromes

Multiple endocrine neoplasia type 1 affects about 1 in 30,000 people; multiple endocrine neoplasia type 2 affects an estimated 1 in 35,000 people. Among the subtypes of type 2, type 2A is the most common form, followed by FMTC. Type 2B is relatively uncommon, accounting for about 5 percent of all cases of type 2. The prevalence of multiple endocrine neoplasia type 4 is unknown, although the condition appears to be rare.

Mutations in the MEN1, RET, and CDKN1B genes can cause multiple endocrine neoplasia.

Mutations in the MEN1 gene cause multiple endocrine neoplasia type 1. This gene provides instructions for producing a protein called menin. Menin acts as a tumor suppressor, which means it normally keeps cells from growing and dividing too rapidly or in an uncontrolled way. Although the exact function of menin is unknown, it is likely involved in cell functions such as copying and repairing DNA and regulating the activity of other genes. When mutations inactivate both copies of the MEN1 gene, menin is no longer available to control cell growth and division. The loss of functional menin allows cells to divide too frequently, leading to the formation of tumors characteristic of multiple endocrine neoplasia type 1. It is unclear why these tumors preferentially affect endocrine tissues.

Mutations in the RET gene cause multiple endocrine neoplasia type 2. This gene provides instructions for producing a protein that is involved in signaling within cells. The RET protein triggers chemical reactions that instruct cells to respond to their environment, for example by dividing or maturing. Mutations in the RET gene overactivate the protein's signaling function, which can trigger cell growth and division in the absence of signals from outside the cell. This unchecked cell division can lead to the formation of tumors in endocrine glands and other tissues.

Mutations in the CDKN1B gene cause multiple endocrine neoplasia type 4. This gene provides instructions for making a protein called p27. Like the menin protein, p27 is a tumor suppressor that helps control the growth and division of cells. Mutations in the CDKN1B gene reduce the amount of functional p27, which allows cells to grow and divide unchecked. This unregulated cell division can lead to the development of tumors in endocrine glands and other tissues.

Read more about the CDKN1B, MEN1, and RET genes.

Most cases of multiple endocrine neoplasia type 1 are considered to have an autosomal dominant pattern of inheritance. People with this condition are born with one mutated copy of the MEN1 gene in each cell. In most cases, the altered gene is inherited from an affected parent. The remaining cases are a result of new mutations in the MEN1 gene, and occur in people with no history of the disorder in their family.

Unlike most other autosomal dominant conditions, in which one altered copy of a gene in each cell is sufficient to cause the disorder, two copies of the MEN1 gene must be altered to trigger tumor formation in multiple endocrine neoplasia type 1. A mutation in the second copy of the MEN1 gene occurs in a small number of cells during a person's lifetime. Almost everyone who is born with oneMEN1 mutation acquires a second mutation in certain cells, which can then divide in an unregulated way to form tumors.

Multiple endocrine neoplasia type 2 and type 4 are also inherited in an autosomal dominant pattern. In these cases, one copy of the mutated gene is sufficient to cause the disorder. Affected individuals often inherit an altered RET or CDKN1B gene from one parent with the condition. Some cases, however, result from new mutations in the gene and occur in people without other affected family members.

For more information about naming genetic conditions, see the Genetics Home Reference Condition Naming Guidelines and How are genetic conditions and genes named? in the Handbook.