Testing & diagnosis for fragile x syndrome in children

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Contact the Fragile X Program

The first step in treating your child is forming an accurate diagnosis. Fragile X may be challenging to diagnose, or may be diagnosed later in life, because many people—even doctors—aren’t familiar with it.

Girls, in particular, may go undiagnosed because people still think they can’t have fragile X, and/or because their symptoms may be extremely mild.

To diagnose your child, blood is taken and analyzed for the fragile X gene. Then we will meet with you and your family to discuss the results and outline the best treatment options.

How do I know if my child should be tested for fragile X?

The current recommendation is that any boy with intellectual delay should be tested for the fragile X gene. There isn’t a similar recommendation for girls, although specialists familiar with fragile X would likely test girls who show learning disabilities coupled with mood or behavior disorders, such as anxiety and attention-deficit hyperactivity disorder (ADHD).

When are children diagnosed with fragile X?

Boys with fragile X are usually diagnosed within the first three years of life. Problems often start to become obvious in second year, when they’re delayed in speech development and social interactions may start to go awry.

Since girls have fewer symptoms, they tend to be diagnosed much later, often in their early teens. The diagnosis is usually made by a pediatrician, neurologist, geneticist, or developmental specialist.

Can fragile X be diagnosed during pregnancy?

The fragile X gene can be detected during pregnancy, but even if the test shows the full mutation, it’s impossible to know what any symptoms your child will have (or even if she or he will have any at all).

Prenatal diagnosis can be done through:

Chorionic villus sampling (CVS)

  • typically performed at 10 to 12 weeks gestation
  • a preliminary result is available in the first trimester, although confirmation may not be available until the second trimester
  • results from CVS analysis may be difficult to interpret; for further details, talk to your genetic counselor

Amniocentesis (a test of the amniotic fluid)

  • typically performed at 15 to 18 weeks gestation
  • results are generally available in about 4 weeks

Should I be tested for fragile X during my pregnancy?

You should be tested if you know that you are a carrier of the fragile X gene or if there is a history of fragile X in your family. If you are not a carrier, but are concerned about fragile X, talk with your genetic counselor.

What should I do after my child is diagnosed with fragile X?

After your child is diagnosed with fragile X, contact a fragile X program. To talk to us at Children’s Hospital Boston, call our Fragile X Program at 617-355-4697, and we will arrange a time to meet with you and your child.

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