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What is ataxia-telangiectasia?
Ataxia-telangiectasia (A-T) is a hereditary condition characterized
by progressive neurologic problems that lead to difficulty walking.
Signs of A-T often develop in childhood. Children with A-T may begin
staggering and appear unsteady (ataxia) shortly after learning to walk.
Most people with A-T will eventually need to use a wheelchair. People
with A-T have normal intelligence, but over time, they will develop
slurred speech and have difficulty with writing and other tasks. Red
marks called telangiectasias are caused by dilated capillaries (tiny
blood vessels) and appear on the skin and eyes as people get older.
People with A-T also have a weakened immune system and are prone to
infections. In addition, they appear to be particularly sensitive to
ionizing radiation (such as x-rays) and have an increased risk of
cancer.
What causes A-T?
A-T is a genetic condition. This means that the risk for A-T can be
passed from generation to generation in a family. The gene associated
with A-T is ATM (ataxia telangiectasia mutated). Mutations (changes) in the ATM gene cause A-T.
How is A-T inherited?
Normally, every cell has two copies of each gene: one inherited from
the mother and one inherited from the father. A-T follows an autosomal
recessive inheritance pattern. In autosomal recessive inheritance, a
mutation must be present in both copies of the gene in order for a
person to be affected. This means that each parent must pass on a gene
mutation for a child to be affected. A person who has only one copy of
the gene mutation is called a carrier. When both parents are carriers of
a recessive gene mutation, there is a 25% chance that a child will
inherit two mutations and be affected.
How common is A-T?
A-T is rare. It is estimated that A-T affects one in 40,000 to one in
100,000 individuals. The chance that a person is a carrier of a single ATM gene mutation is about 1%, or one in 100.
How is A-T diagnosed?
A-T is suspected whenever a child develops signs of ataxia (unsteady walking). Testing of the ATM
gene is available, and about 90% of mutations can be found. The
following tests may be more helpful in determining if someone has A-T or
another type of ataxia:
Immunoblotting (ATM protein testing). This is
the best test to diagnose A-T. Nearly all individuals with A-T will
have very low or no amounts of the protein made by the ATM gene.
Radiosensitivity assay. Since people with A-T have
an increased sensitivity to radiation, removing some cells and treating
the sample with radiation therapy can help make the diagnosis. It can
take up to three months to get a result from this test.
ATM kinase activity. This test looks at the activity level of the protein made by the ATM gene. Little to no activity means that there is likely a mutation in the ATM gene.
What are the estimated cancer risks associated with A-T?
People with A-T also have about a 40% risk of developing cancer. The
most common types of cancer seen in people with A-T are leukemia and
lymphoma. These two types of cancers can appear in childhood and account
for 85% of all cancers in people with A-T. As people with A-T live
longer, there appears to be an increased risk of other cancer types,
including breast cancer, ovarian cancer, stomach cancer, melanoma, and sarcoma.
Carriers (people with one ATM gene mutation) also seem to have
an increased cancer risk. It is estimated that carriers have a 4%
increase in cancer risk compared with the general population. Of
particular concern is the potential breast cancer risk in women who
carry an ATM gene mutation. Some studies have shown a large
increase in breast cancer risk for women who are carriers, while other
studies have shown no increased risk. Additional research is needed to
clarify the cancer risk for ATM mutation carriers. Studies also show that carriers may have an increased risk of heart disease.
What are the screening options for A-T?
Children and adults with A-T should see their doctor regularly and be
monitored for signs of cancer. Individuals with A-T who frequently
develop infections are encouraged to have their immune status checked
regularly.
There are no specific cancer screening or prevention recommendations
for individuals with A-T or gene mutation carriers. However, women who
are carriers are encouraged to talk with their doctor about breast
cancer screening options.
Screening options may change over time as new technologies are
developed and more is learned about A-T. It is important to talk with
your doctor about appropriate screening tests.
Learn more about what to expect when having common tests, procedures, and scans.
Questions to ask the doctor
If you are concerned about your risk of cancer, talk with your doctor. Consider asking the following questions of your doctor:
- What is my risk of developing cancer?
- What can I do to reduce my risk of cancer?
- What are my options for cancer screening?
If you are concerned about your family history and think your family may have A-T, consider asking the following questions:
- Does my family history increase my risk of developing cancer?
- Could my family have A-T?
- Should I meet with a genetic counselor?
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