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What is fragile X syndrome?

Fragile X syndrome is a genetic condition that can cause a range of learning and developmental problems. These can include:

Some children with fragile X may also have mildly characteristic features such as prominent ears.

Fragile X is more common in boys than girls, and boys with fragile X usually have more severe symptoms.

Are there any medical concerns with fragile X?

Unlike many other genetic conditions, fragile X syndrome does not cause many medical complications. Health problems in children with fragile X may include:

As adults, people with fragile X may also develop:

  • Mitral valve prolapse (leaky heart valve); this is seen in about half of all adults with fragile X
  • Aortic enlargement in a small proportion
  • High blood pressure that can be treated with medication
  • Scoliosis

Symptoms & Causes

What are the symptoms of fragile X syndrome?

Both boys and girls with fragile X can have certain behavioral and intellectual traits, though girls often have milder symptoms.

Kids with fragile X may have:

  • Delayed speech
  • Delayed motor skills
  • Repetitive and unclear speech (especially in boys)
  • Autistic-like behaviors, including poor eye contact, hand biting, hand flapping, and sensitivity to noise and crowds
  • Learning difficulties
  • Social anxiety
  • Hyperactivity and short attention spans (especially in boys)
  • Shyness (mostly seen in girls)

Some children with fragile X also have physical traits, which may become more noticeable after puberty:

  • Large ears
  • A long and narrow face
  • Flat feet
  • In boys: large, but functional, testicles
  • Very flexible joints

Because the symptoms of fragile X are similar to, or may mimic, those of other conditions, such as autism and Prader-Willi syndrome, it’s important to see a doctor for an exact diagnosis.

What causes fragile X syndrome?

Fragile X is caused by a mutation in the FMR1 gene that prevents the body from making an important protein, called FMRP. This protein helps create and maintain connections between brain cells and the nervous system. When FMRP is missing, signals from the brain may be misdirected. This causes the developmental and learning problems found in fragile X.

The FMR1 gene is found on the X chromosome, which means that females (who have two X chromosomes) have two copies of the FMR1 gene, and males (who have one X chromosome) have only one. If this one X chromosome is not working, there’s no backup. This is why boys often have more severe symptoms than girls.

Diagnosis & Treatments

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.
  • Amniocentesis: this 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.

What is the treatment for fragile X syndrome?

There is no one single treatment that is right for every child with fragile X. Treatment is based on a child’s individual symptoms and needs. Some common treatments for children with fragile X include:

  • Speech and language therapy to improve communication skills
  • Occupational therapy and physical therapy to help with daily activities such as self-care, chores, and hobbies
  • Sensory issues
  • Developmental medicine and special education to work on any educational weaknesses and help develop good learning strategies
  • Psychiatry and other behavioral health care to help with any behavioral or emotional problems
  • Medication to help with symptoms of fragile X, such as seizures, or mood or behavioral problems

Our expert care for fragile X syndrome

At the Boston Children's Hospital Fragile X Program, we’re focused on family centered care to support all of your child’s physical and social needs. Our team can put you in touch with other families who have a child with fragile X and connect you with community and educational services.

Practitioners Who Specialize In This Condition (9)

Hope Dickinson, MS, CCC-SLP

Hope Dickinson, MS, CCC-SLP

Director, Speech-Language Pathology Program; Speech-Language Pathologist, Department of Otolaryngology and Communication Enhancement
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