Ataxia telangiectasia


Ataxia telangiectasia

Description, Causes and Risk Factors:

ICD-10: G11.3

Ataxia telangiectasia is a hereditary progressive neurodegenerative disorder that begins in early childhood. The most debilitating symptom is the progressively worsening ataxia or loss of balance.

In the US, ataxia telangiectasia is the second most common recessive ataxia of childhood. In countries where marriage between cousins is uncommon, such as in the US, the incidence is about 1 in 40,000 live births. However, among ethnic groups where cousin-cousin marriages are common, the incidence increases significantly. The carrier frequency is approximately 1 in 100 persons.

Ataxia telangiectasia

The underlying problem is a gradual and continual loss of certain types of cells in the cerebellum of the brain, which control and coordinate the movement of limbs, fingers, eyes, tongue, etc. It is thought that because the cells lack a protein named ATM (for ataxia-telangiectasia mutated), they do not recognize and repair breaks in the DNA (which carries the code for our genes). These DNA breaks occur all the time in all of us. But because the ATM protein controls over 700 other proteins that help cells to repair DNA, when there is not enough ATM protein, the DNA damage accumulates and eventually leads to the death of individual cells, especially in the central nervous system.

Ataxia telangiectasia is inherited as an autosomal recessive disorder. The gene responsible for ataxia telangiectasia has been identified and is found on the long arm of chromosome 11 at 11q22-23. It controls the production of a phosphatidylinositol-3-kinase-like enzyme involved in cellular responses to stress, DNA damage and cell cycle control. The identification of the specific gene responsible for ataxia telangiectasia has made carrier detection and prenatal diagnosis possible, though it can be done only in a few specialized laboratories and is very expensive.

Boys and girls are equally affected.

Symptoms:

Symptoms may include:

    Ataxic, jerky, and unsteady gait.

  • Decreasing mental development, slows or stops after age 10-12.

  • Delayed walking.

  • Discoloration of skin areas exposed to sunlight.

  • Discoloration of skin (coffee-with-milk colored spots).

  • Enlarged blood vessels in skin of nose, ears, and inside of the elbow and knee.

  • Enlarged blood vessels in the whites of the eyes.

  • Jerky or abnormal eye movements (nystagmus) late in the disease.

  • Premature graying of the hair.

  • Seizures.

  • Sensitivity to radiation, including medical x-rays.

  • Severe respiratory infections that keep coming back (recurring).

Diagnosis:

The diagnosis of ataxia telangiectasia isusually based on characteristic clinical findingsand supported by laboratory tests. An alpha-fetoprotein (AFP) test is elevated in the blood in >95% of patients. Karyotyping usually reveals characteristictranslocations between chromosomes 7 and 14. An MRI will show (after 7 or 8 years of age) that the cerebellum isshrinking in size. The absence of ATM protein and its various functions can be documented in the laboratory by a bloodtest. The sensitivity of ataxia telangiectasia cells to ionizing radiation is also markedly increased. In an experienced laboratory, DNAsequencing can confirm the presence of mutations in both copies of the very large ATM gene. DNA sequencing can alsobe used to identify carriers; however, this is expensive because of the size of the gene. A more rapid method of carrierdetection is being developed.

Other Tests May Include:

    Alpha fetoprotein.

  • B and T cell screen.

  • Carcinoembryonic antigen.

  • Glucose tolerance test.

  • Serum immunoglobulin levels (IgE, IgA).

Treatment:

There is no cure for any of the problems in ataxia telangiectasia, and treatment is largely supportive. Patients of all ages should be encouraged to participate in as many activities as possible. Children should be able to attend school on a regular basis, but most will eventually need full-time classroom aides. Progressive eye movement abnormalities make reading difficult, but listening skills do not deteriorate. As a result, it is helpful to introduce books-on-tape at a young age to foster development of listening skills. Computers are also helpful learning aides that can be easily adapted to the specific needs of an individual who has problems with eye and hand coordination. Physical and occupational therapists should be included in the treatment team to prevent the development of stiffness in muscles and to maintain functional mobility.

For patients with total IgG, or IgG subclass deficiencies, and/or patients who have problems making normal antibody responses to vaccines, immunoglobulin replacement therapy may be indicated. In an effort to decrease exposure to the flu, all household members should receive the flu vaccine every fall.

Special attention should be paid to the lungs. Ataxia telangiectasia patients have difficulty taking deep breaths and coughing to clear mucus from the airways. They may benefit from daily chest physiotherapy or use of a therapy vest. If chronic lung disease develops, a lung specialist should be consulted about the use of intermittent antibiotic prophylaxis, inhaled medicines to decrease airway inflammation or constriction and the need for supplemental oxygen while sleeping. Many ataxia telangiectasia patients develop problems with chewing and swallowing. Those who aspirate (have food and liquids entering their windpipe and lungs) may improve when thin liquids are eliminated from their diet. In some individuals, a tube from the stomach to the outside of the abdomen (gastrostomy tube) may be necessary to eliminate the need for swallowing large volumes of liquids and to decrease the risk of aspiration.

NOTE: The above information is educational purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.

DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.

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