The thymus gland is a small gland in your upper chest that has importance for your health far out of proportion to its size. It starts functioning during fetal life, manufacturing millions of immune cells called T cells. In a complex process, the thymus educates these cells to identify and attack foreign invaders and to recognize and ignore your own body's proteins and cells. Cells from the thymus circulate in your blood and reside in various organs, where they help protect you from illness. Disorders of the thymus gland are relatively rare, but they can be potentially serious.
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Several genetic defects cause thymus problems from birth. A rare condition called severe combined immunodeficiency, or SCID, develops when a person carries a mutation in a gene that regulates development of T cells. Affecting roughly 1 in every 40,000 to 100,000 babies born in the United States, SCID disrupts the normal development of T cells in the thymus and other immune cells. This severely compromises a child's immune system, making him unable to fight off infections. In another rare disorder called DiGeorge syndrome, a piece of a chromosome is missing along with the genes it contains. This leads to poor development of the thymus and other organs in the immune system, causing weak immune responses and frequent illness. The severity of the disorder varies and can cause mild to severe symptoms.
In disorders called autoimmune diseases, the immune system attacks the body's own cells or substances made by cells, incorrectly perceiving them as foreign and harmful. One of these disorders, myasthenia gravis, is associated with a thymus gland that does not shrink but remains large after birth and functions abnormally. Although the disorder isn't fully understood, the thymus appears to be abnormally overactive, producing cells that attack a neurotransmitter called acetylcholine, which promotes normal muscle contraction in response to nerve impulses. The disease typically causes muscle weakness, often first seen in the eye muscles. Other symptoms include difficulty swallowing, slurred speech and other problems related to poor muscle function.
Although rare, 2 types of cancer can develop it the thymus called thymomas and thymic carcinomas. Both develop in populations of cells on the surface of the thymus, but they differ in other respects. Cells in thymomas grow relatively slowly. Thymic carcinoma cells divide rapidly and can quickly spread to other parts of the body. People with myasthenia gravis and other autoimmune disorders are at increased risk for thymomas. Symptoms of thymus cancer may include a cough that doesn't improve, trouble breathing and chest pain. In some cases, few if any symptoms are present in the early stages of the disease.
Each type of thymic disorder can be treated and, in many cases, effectively controlled or cured. Congenital immunodeficiency such as that caused by SCID has been successfully treated through bone marrow transplantation or gene therapy. A severe case of DiGeorge syndrome might be treated with a thymus transplant, with milder forms responding to an infusion of extra immune cells. Treatments for myasthenia gravis depend on disease severity. The condition is often controlled through use of medications that improve muscle function or suppress production of abnormal antibodies made by immune cells. Treatments for thymic cancer vary, depending on whether and how far the cancer has spread. Options include surgery, chemotherapy drugs and radiation therapy.