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Ataxia Telangiectasia

Ataxia-telangiectasia (A-T) is a rare inherited disorder of childhood that affects the nervous system, immune system, and other body systems. This condition occurs in 1 in 40,000 to 100,000 people worldwide.

Symptoms

Ataxia-telangiectasia is characterized by progressive difficulty with coordinating movements (ataxia) beginning in early childhood, usually before age 5. Affected children typically develop difficulty walking, problems with balance and hand coordination, involuntary jerking movements (chorea), muscle twitches (myoclonus), and disturbances in nerve function (neuropathy). The movement problems typically cause people to require wheelchair assistance by adolescence. People with this disorder also have slurred speech and trouble moving their eyes to look side-to-side (oculomotor apraxia). Small clusters of enlarged blood vessels called telangiectases, which occur in the eyes and on the surface of the skin, are also characteristic of this condition.

Affected individuals tend to have high amounts of a protein called alpha-fetoprotein (AFP) in their blood. The level of this protein is usually increased in the bloodstream of pregnant women. The effect of abnormally high levels of AFP in people with ataxia-telangiectasia is unknown.

People with ataxia-telangiectasia often have a weakened immune system, and many develop chronic lung infections. They are also at an increased risk of developing cancer, particularly cancer of blood-forming cells (leukemia) and cancer of immune system cells (lymphoma). Affected individuals are very sensitive to the effects of radiation exposure, including medical x-rays. Although people with ataxia-telangiectasia usually live into adulthood, their life expectancy is reduced.

Causes

Mutations in the ATM gene cause ataxia-telangiectasia.

The ATM gene provides instructions for making a protein that helps control cell division and is involved in DNA repair. This protein plays an important role in the normal development and activity of several body systems, including the nervous system and immune system. Mutations in the ATM gene reduce or eliminate the function of the ATM protein. Without this protein, cells become unstable and die inappropriately, particularly affecting cells in a part of the brain involved in coordinating movements (the cerebellum). The loss of these brain cells causes the movement problems characteristic of ataxia-telangiectasia. Mutations in the ATM gene also prevent cells from responding correctly to DNA damage, which allows breaks in DNA strands to accumulate and can lead to the formation of cancerous tumors.

How do people inherit ataxia-telangiectasia?

Ataxia-telangiectasia is inherited in an autosomal recessive pattern, which means both copies of the ATM gene in each cell have mutations. Most often, the parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but do not show signs and symptoms of the condition.

About 1 percent of the United States population carries one mutated copy and one normal copy of the ATM gene in each cell. Although ATM mutation carriers do not have ataxia-telangiectasia, they are more likely than people without an ATM mutation to develop cancer, particularly breast cancer. Carriers of a mutation in the ATM gene also may have an increased risk of heart disease and diabetes.

Treatment

There is no cure for A-T and, currently, no way to slow the progression of the disease. Treatment is symptomatic and supportive. Physical and occupational therapy may help maintain flexibility. Speech therapy may also be needed. Gamma-globulin injections may be given to help supplement a weakened immune system. High-dose vitamin regimens may also be used.

The prognosis for individuals with A-T is poor. Those with the disease usually die in their teens or early 20s.

 

Sources

Genetics Home Reference, U. S. National Library of Medicine

National Institute of Neurological Disorders and Stroke