Fragile X Syndrome (FXS)

Fragile X syndrome is the leading cause of inherited intellectual disabilities like autism spectrum disorder. There are behavioral, physical, intellectual and mental health symptoms. Women and people assigned female at birth have milder symptoms than men and people assigned male at birth. Although there isn’t a cure, medication and therapy can help manage symptoms.


What is fragile X syndrome?

Fragile X syndrome (FXS) is an inherited genetic disorder that causes physical abnormalities, behavioral issues and a wide range of other health problems, including:

Fragile X syndrome is the most common form of inherited intellectual and developmental disability (IDD). It gets its name because when you look at the X chromosome through a microscope, part of it looks “broken” or “fragile.” Another name for the condition is Martin-Bell syndrome.

How common is fragile X syndrome?

Researchers don’t know the exact number of people with fragile X syndrome. But they estimate that, worldwide, about 1 in 11,000 people assigned female at birth (AFAB) and 1 in 7,000 people assigned male at birth (AMAB) have fragile X syndrome.


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Symptoms and Causes

Fragile X syndrome symptoms, like intelligence, mental health, physical features and behavioral issues
Fragile X syndrome (FXS) is an inherited genetic disorder that causes physical abnormalities, behavioral issues and a wide range of other health problems.

What are the symptoms of fragile X syndrome?

Fragile X syndrome affects your child’s intelligence, mental health, physical features and behavior. Common fragile X syndrome symptoms in each category include:

Intelligence issues

  • Learning disabilities.
  • Low intelligence quotient (IQ). Their IQ scores decrease with age.
  • Delayed early developmental milestones.
  • Delayed development of nonverbal communication, like using gestures, body language and facial expressions.
  • Language processing issues. You may notice that your child struggles with speech and language at about age 2.
  • Problems with math.

Talk to your child’s healthcare provider about exactly what milestones to watch out for and how to evaluate them.

Mental health problems

Physical features

What are the behavioral symptoms of fragile X syndrome?

Fragile X syndrome may cause a range of behavioral issues, like:

  • Attention-deficit/hyperactivity disorder (ADHD).
  • Social anxiety and shyness.
  • Flapping or biting their hands.
  • Poor eye contact.
  • Sensory disorders — sensitivity to crowds, touch, sounds, foods and textures.
  • Difficulty picking up social cues.

What causes fragile X syndrome?

A genetic mutation of the FMR1 gene on the X chromosome causes fragile X syndrome. The FMR1 gene is responsible for providing instructions to your body for making a protein called FMRP. This protein has a vital role in the development of synapses — specialized connections between your nerve cells that are critical for relaying nerve impulses.

A mutation in the FMR1 gene causes a DNA part within it called the CGG triplet repeat to expand. A typical part repeats five to 40 times, but in people with fragile X syndrome, it repeats more than 200 times. This “silences” the FMR1 gene, which disrupts your child’s nervous system and causes the symptoms of fragile X syndrome.

What is the inheritance pattern of fragile X syndrome?

The fragile X syndrome inheritance is in an X-linked dominant pattern. That means the mutated gene that causes it is located on the X chromosome. The inheritance is dominant because only one copy of the mutated gene is necessary to cause the condition.

Fragile X syndrome occurs more frequently in men and people AMAB because they only have one X chromosome. Their symptoms are also more severe. Women and people AFAB have two X chromosomes. The condition may not affect both X chromosomes. Therefore, women and people AFAB can be carriers without having symptoms, but men and people AMAB with fragile X will always have symptoms.

Are carriers of fragile X at risk of any health problems?

Yes. If your child has fragile X syndrome, you should tell your healthcare provider. As a possible carrier, you’re at a higher risk for:


What are the complications of fragile X syndrome?

Sometimes people with fragile X syndrome develop other health conditions. In one study, parents reported that their children also had:

  • Seizures.
  • Sleep issues. According to a different study, 4 in 10 people with fragile X and autism spectrum disorder had sleeping problems. This is compared to 3 in 10 people who have only fragile X.
  • Aggressiveness or irritability. People with fragile X syndrome in addition to autism spectrum disorder are more likely to be aggressive.
  • Self-injury behaviors.
  • Obesity.

Diagnosis and Tests

How is fragile X syndrome diagnosed?

Diagnosing fragile X syndrome requires a DNA sample from your child’s blood or other tissues. Your child’s healthcare provider will send the sample to a laboratory that will determine if your child has the FMR1 gene.

If you’re pregnant and concerned that your child has fragile X syndrome, you can see a genetic counselor where you may undergo the following prenatal tests:

At what age is fragile X syndrome diagnosed?

Children assigned male at birth (AMAB) usually receive a diagnosis at 35 to 37 months old. Children assigned female at birth (AFAB) may receive a diagnosis a little later — at about 42 months old. But you may start to notice symptoms in your child as early as 12 months.


What questions might a healthcare provider ask to help diagnose fragile X syndrome?

Before your child’s healthcare provider or a genetic counselor orders a test for fragile X syndrome, they may ask you the following questions:

  • What symptoms have you noticed in your child?
  • How well does your child learn?
  • Is your child shy?
  • Does your child have sleep problems?
  • Is your child anxious?
  • Does your child avoid eye contact?
  • Does your child have any abnormal physical features?
  • How is your child’s speech?

Can you be diagnosed with fragile X syndrome as an adult?

While fragile X syndrome is typically diagnosed in children, two other syndromes in the fragile X family may be diagnosed in adults:

  • Fragile X-associated tremor/ataxia syndrome (FXTAS): Symptoms include balance issues, shaky hands, unstable mood, memory loss, cognitive problems and numbness in your hands and feet.
  • Fragile X-associated primary ovarian insufficiency (FXPOI): Symptoms include reduced fertility, infertility, missing or unpredictable menstrual periods, and premature menopause.

If you have symptoms of either of these conditions, talk to a healthcare provider.

Management and Treatment

How is fragile X syndrome treated?

Fragile X syndrome doesn’t have a cure, but you can treat the symptoms of the condition. Your child’s healthcare provider may prescribe a variety of fragile X syndrome medications. Examples of medications, categorized by symptom, include:

Seizures or mood instability:


Aggression or obsessive-compulsive disorder:

Sleep issues:

This is just a short list of possible medications your child’s healthcare provider may prescribe. Talk to their provider about possible side effects and complications that may come with each medication.

Your child’s provider will likely also recommend psychotherapy as part of your child’s fragile X syndrome treatment — therapy that helps with coping and behavioral skills.


Can fragile X syndrome be prevented?

No, fragile X syndrome is a genetic condition and you can’t prevent it. If you’re pregnant or thinking about becoming pregnant, you may wish to speak with a genetic counselor about your risk of passing on the condition to your child.

Outlook / Prognosis

What’s the outlook for people with fragile X syndrome?

Some people with fragile X syndrome can live independently. Studies show that about 4 in 10 people AFAB and 1 in 10 people AMAB with fragile X syndrome grow up to have a high level of independence. People AFAB have the following abilities more than people AMAB:

  • Reading books that include new ideas and new words.
  • Speaking complex sentences.
  • Speaking at a typical speed.

Fragile X syndrome is generally more severe in people AMAB, so people AFAB with the condition thrive more than people AMAB. About 8 out of 20 people AFAB with fragile X don’t need help with daily activities. The same can be said for only 1 in 20 people AMAB. Most people AFAB get a high school diploma but a majority of people AMAB don’t. Nearly half of people AFAB with fragile X have full-time jobs but only 2 in 10 people AMAB do.

Can my child attend daycare/school?

Your child may need special accommodations at daycare or school. Some parts of the school day and classroom may need to be adjusted to fit their needs. Your child’s teacher might be able to make environmental adjustments and curricular adjustments.

Environmental adjustments:

  • Keep the noise level down.
  • Have natural lighting.
  • Avoid crowds.

Curricular adjustments:

  • Have visual aids like diagrams, charts, color coding or pictures.
  • Help your child learn by using materials they find very interesting.
  • Have your child work in small groups.

Be sure to inform your child’s school that your child has fragile X syndrome. Have a conversation with their teacher about their unique needs. You may also meet with a school psychologist and/or counselor. They work with children 3 years old and older. Other specialists you may want to connect with include:

Talk with your local school and healthcare providers for referrals.

How long does fragile X syndrome last?

Fragile X syndrome is a lifelong condition. There’s no cure.

What is the life expectancy of fragile X syndrome?

None of the symptoms of fragile X syndrome are life-threatening. The fragile X syndrome life expectancy is the same as for the average person.

Living With

What is life like with fragile X syndrome?

Fragile X syndrome affects every child differently. Your child’s healthcare team will be able to give you a better idea of how it’ll affect your child and family. While aspects of the condition can be challenging, there are many positive characteristics. For example, researchers have noted that people with fragile X are:

  • Helpful.
  • Kind.
  • Thoughtful.
  • Friendly.
  • Good imitators.
  • Good at visual and long-term memory.
  • Humorous.

How do I help my friend or family member with fragile X syndrome?

Educate yourself as much as possible. Look for support groups and community resources that can help you and them. Life skills programs may be appropriate. Some provide guidance about:

  • Social activity.
  • Sexuality.
  • Recreation.
  • Education.
  • Employment.

It’s important to advocate for your child to make sure they get the care they need and have the best possible quality of life.

When should my child see a healthcare provider?

Take your child in to see their pediatrician as soon as you notice the symptoms of fragile X syndrome. Don’t wait, as early intervention is important.

What questions should I ask my child’s healthcare provider?

The following are some questions you may want to ask your child’s healthcare provider when you discuss their diagnosis:

  • Should my child see a specialist?
  • What therapists should my child see?
  • How severe is fragile X syndrome?
  • What medications are appropriate for my child?
  • How can I help my child?
  • What are my early intervention options?
  • How can we help my child as a family?

A note from Cleveland Clinic

Fragile X syndrome can be a difficult diagnosis for you and your child. It’s the start of a lot of change and adjustment. Therapy, medications and accommodations at school are now part of your child’s life. While helping your child, be sure not to neglect your own needs. Remember that if your child has fragile X syndrome, that means you’re more vulnerable to depression, migraines and many other health conditions.

Medically Reviewed

Last reviewed on 02/07/2024.

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