Agammaglobulinemia, x-linked

Diagnosis and Testing

How do I get tested for X-linked agammaglobulinemia?

It may be hard for a primary care physician to recognize X-linked agammaglobulinemia. Frequent symptoms such as ear or respiratory infections are common in childhood. If a boy has persistent middle ear or sinus infections or recurrent pneumonia before the age of 5, X-linked agammaglobulinemia should be considered. It should also be considered if he has severe bacterial infections. This is particularly true for children who also have small or absent tonsils and lymph nodes. If X-linked agammaglobulinemia is suspected, a doctor will order blood tests that can show low levels of antibodies, the specialized proteins that fight of bacteria, virus and other foreign substances in the body. More complex tests that can show a change in the BTK gene can also be ordered to confirm the diagnosis. A patient may be referred to a specialist such as an immunologist. A referral to a local genetics clinic or may also be made. A genetic professional can also be found on the Genetic Testing Registry Homepage.

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Is there newborn testing for X-linked agammaglobulinemia?

Is there more than one test for X-linked agammaglobulinemia?

Who else in my family should I test for X-linked agammaglobulinemia?

Can X-linked agammaglobulinemia be detected before birth?

Is there newborn testing for X-linked agammaglobulinemia?

As of May 2016 X-linked agammaglobulinemia is not one of the disorders detected through newborn screening, however, it may be detected through the newborn screening done for Severe Combined Immunodeficiency (SCID), a group of inherited disorders that cause babies to be born without a working immune system.

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Is there more than one test for X-linked agammaglobulinemia?

There are a few tests that can be used to diagnose X-linked agammaglobulinemia. A doctor may order a blood test that can show low levels of immunoglobulins. Immuoglobulins are the various antibodies normally found in a person's blood. These antibodies are specialized proteins that fight of bacteria, viruses and other foreign material in the body. People with X-linked agammaglobulinemia have very low or virtually absent levels of these antibodies in their blood. A blood test can also show low levels of white blood cells called B cells. These cells produce antibodies. People with X-linked agammaglobulinemia do not have enough of these cells (which is why they lack antibodies).

A diagnosis can be also be made through molecular genetic testing. These tests involve studying the BTK gene for changes that cause the disorder. This may include sequence analysis and deletion/duplication analysis; these are different methods of looking at a gene to detect changes that can cause disease. Molecular genetic testing must be done at specialized laboratories.

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Who else in my family should I test for X-linked agammaglobulinemia?

In a family with X-linked agammaglobulinemia, tests can be done to see whether other family members are carriers for the disorder. However, the specific gene changes in that family needs to be known. If known, all siblings and other at-risk relatives can be tested. Molecular genetic testing, which looks for changes to genes, can be performed. A newborn boy in a family with a history of X-linked agammaglobulinemia should be tested through molecular genetic testing. Confirming a diagnosis allows therapy to be started as soon as possible. Women or girls can be tested to see if they carry the altered gene. A genetic counselor or a physician with experience in X-linked agammaglobulinemia can provide advice about how a confirmed diagnosis can affect other family members. A genetic professional can also be found on the Genetic Testing Registry Homepage.

References
Can X-linked agammaglobulinemia be detected before birth?

Some parents may choose to have their child tested for X-linked agammaglobulinemia (XLA) before birth. This is known as prenatal diagnosis. First, the specific change in the BTK gene that is causing XLA in the family must be known. Then, a procedure is done during the pregnancy, either a chorionic villus sampling (CVS) or amniocentesis. During a CVS, a sample of tissue is taken from the placenta, usually around 10-12 weeks into the pregnancy. Amniocentesis involves taking a sample of the amniotic fluid that surrounds and protects a developing fetus. Cells known as amniocytes are taken from the fluid and studied. It is usually performed around 15-18 weeks into the pregnancy. If the tests show the fetus is a boy then the cells can be tested for an altered BTK gene.

Families considering prenatal testing should set up an appointment with a genetic counselor. A genetic counselor can explain the testing options and discuss reasons a family may or may not want to do prenatal diagnosis for XLA. A genetic counselor can also explain the test results. Genetic counselors can be found on the National Society of Genetic Counselors website.

References

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