Fragile X Syndrome | Testing and Diagnosis

How is fragile X syndrome diagnosed?

Fragile X is diagnosed with a blood test to check for the fragile X gene.

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

You should consider having your child tested for fragile X if he or she has any autism-like behaviors, developmental delays, speech or language delays or learning disabilities.

At what age are children usually diagnosed with fragile X?

Most parents start to notice symptoms when their children are infants or toddlers. Boys with fragile X are usually diagnosed by age 3. Since girls tend to have milder symptoms, they are often not diagnosed until later.

Can fragile X be diagnosed during pregnancy?

The fragile X gene can be detected during pregnancy, but even if the test shows the mutation, it’s impossible to know which, if any, symptoms a child will have or how severe they will be. You should consider prenatal testing if you know you’re a carrier of the fragile X gene or if there is a history of fragile X in your family.

Tests for fragile X in pregnancy include:

  • Chorionic villus sampling (CVS)this test is usually done between weeks 10 and 12 of the pregnancy. It checks cells from the placenta for the FMR1 gene.
  • Amniocentesisthis test is usually done between weeks 15 and 18 of the pregnancy. It checks amniotic fluid for the FMR1 gene.

Prenatal tests carry some risks for both mother and baby, so talk with your clinician about the pros and cons before testing. 

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