Fragile X Syndrome

Written by Hallie Levine, Alexandra Benisek
Medically Reviewed by Shruthi N, MD on October 15, 2024
9 min read

Fragile X syndrome, also known as Martin-Bell syndrome, is a genetic condition that affects a child's learning, behavior, appearance, and health. Symptoms can be mild or more severe, and boys often have a more serious form of the condition than girls.

Children born with this condition have developmental concerns, including learning disabilities and limits to mental functions. Special education and therapy can help with learning and developing skills according to their ability. Medications and other treatments can improve their behavior and physical symptoms.

People with fragile X may have several symptoms, including:

  • Trouble learning skills such as sitting, crawling, or walking
  • Language and speech problems
  • Hand-flapping and not making eye contact
  • Temper tantrums
  • Poor impulse control
  • Anxiety
  • Depression
  • Obsessive-compulsive behaviors
  • Extreme sensitivity to light or sound
  • Hyperactivity and trouble paying attention
  • Aggressive and self-destructive behavior in boys
  • Trouble picking up on social cues
  • Seizures
  • Attention deficit disorder (ADD)
  • Autism symptoms that affect communication and how they deal with other people

About 40% of individuals with fragile X also have autism.

If your child has both fragile X and autism, they’re more likely to have seizures, sleep issues, more behavioral issues, and need more medications.

Almost 80% of children with fragile X also have attention deficit disorder (ADD) or attention deficit hyperactivity disorder (ADHD).

Some children with fragile X also have changes to their face and body that can include:

  • A large head
  • A long, narrow face
  • Soft skin
  • Crossed or lazy eyes
  • Low muscle tone
  • A high-arched palate (roof of the mouth)
  • Large ears
  • A large forehead and chin
  • Loose joints
  • Flat feet
  • Enlarged testicles (after puberty)

Signs of fragile X usually start with delayed speech and language trouble by the age of 2, along with delays in motor milestones. Boys are usually diagnosed around the age of 35-37 months. Girls are diagnosed around 42 months old. Symptoms are usually milder in girls. While most boys with fragile X have trouble with learning and development, girls usually don't have these issues.

Girls with fragile X sometimes have trouble getting pregnant when they grow up. They might also go into menopause earlier than usual.

The condition can also cause problems with:

  • Hearing
  • Vision
  • Heart health
  • Sleeping
  • Obesity

Fragile X syndrome is passed down in families through a mutation in the FMR1 gene. The FMR1 gene, which is on the X chromosome, makes a protein called FMR that helps nerve cells talk to one another. A child needs this protein for their brain to develop normally. Children with fragile X make too little or none of it.

People with this condition also have more copies than usual of a DNA segment known as CGG. In most people, this segment repeats 5 to 40 times. In people with fragile X, it repeats more than 200 times. The more times this DNA segment repeats, the more serious the symptoms are.

A mother with the FMR1 gene change has a 50% chance of passing it to any of her children. A father can only pass it to his daughters.

Since the FMR1 gene is on the X chromosome, it is known as an X-linked condition. That means that all males who carry the gene mutation develop symptoms. As a result, boys are more likely to have fragile X than girls and often show more severe symptoms. Girls have two copies of the X chromosome, so even if one X chromosome has the gene change, the other copy can be fine.

About 1 in 151 females and 1 in 468 males carry something known as the FMR1 premutation. That means that their CGG segment repeats anywhere from 55 to 200 times. These pre-mutations usually don’t impact their health, and they don’t show symptoms. But people with pre-mutations can still pass the gene change on to their children. This gene can also change size as it passes from parent to offspring. This means it eventually could develop into a full-blown mutation.

The number isn’t clear, but about 1 in 8,000 to 11,000 females have fragile X syndrome, while 1 in 4,000 to 7,000 males have the condition.

There aren’t any risk factors for fragile X that you can control. If you have the FMR1 gene, your child could have it, too.

While there’s no way to prevent fragile X syndrome, you may want to consider genetic testing.

These tests can be done during pregnancy to see if an unborn baby has fragile X:

After the child is born, a blood test can diagnose fragile X syndrome. This test looks for the FMR1 gene change.

Babies born with fragile X syndrome don't always show signs of it. The doctor might notice that the baby's head is larger than usual. As the child gets older, learning and behavior problems can start.

There are other reasons why adults may want to request fragile X testing. They include:

  • A family history of fragile X syndrome, intellectual or learning disabilities, autism, or infertility
  • A female with unexplained infertility or early menopause
  • An adult over the age of 50 with signs of fragile X-associated tremor/ataxia syndrome (FXTAS), including tremors, memory loss, or personality changes

No medicine can cure fragile X. Treatments can help your child learn more easily and manage problem behaviors. The earlier you start it, the better. Options include:

Special education. Your child will need extra help with learning. It’s important to set up an IEP or 504, which are education plans that guide the school in providing support. Your school may also provide:

  • Speech and language therapy
  • Occupational therapy to help with daily tasks
  • Behavior therapy

Changes to surroundings. You’ll want to make sure your child’s environment, at home and at school, is set up for success. Some ways to do this include:

  • Set routines
  • Visual schedules
  • Transition times
  • Minimal sensory stimuli
  • Medicines to prevent seizures, manage ADD symptoms like hyperactivity, and treat other behavioral problems

Medications. There are no medications to cure Fragile X. There are, however, different drugs that can help manage symptoms. Options include:

  • Antipsychotic medications to help with aggression
  • Antidepressants such as SSRIs, to alleviate anxiety. Many people with Fragile X syndrome begin to show symptoms even as a toddler. 
  • ADHD medications such as stimulants. ADHD symptoms are very common among people with fragile X.
  • The diabetes drug metformin to reduce risk of developing type two diabetes. It may also be used to help to prevent weight gain if your child is taking other medications to manage mood, like antipsychotics.
  • Melatonin to improve insomnia. Sleep problems are common among people with Fragile X.

Many fragile X clinics have opened in the U.S. They can keep parents up-to-date on the latest research, including medications that may be newly available or in clinical trials. The National Fragile X Foundation can be a helpful resource in finding a clinic. 

Fragile X syndrome can cause the following health complications:

  • Frequent ear and sinus infections
  • Obesity
  • Strabismus, or crossed eyes
  • Seizures
  • Trouble sleeping
  • Anxiety or depression
  • Low muscle tone

Fragile X syndrome can also lead to learning and developmental conditions, such as intellectual disability, ADHD, aggression, and autism.

Many adults with fragile X syndrome require a high level of support in adulthood. About a third of women with fragile X can live independently, and almost half are able to have a full-time job. But only about 10% of men with fragile X can live on their own, and only about 20% have a full-time job. 

Most people with a fragile X premutation don’t show any symptoms. But some go on to develop a fragile X-associated disorder. The two most common conditions are:

Fragile X-associated primary ovarian insufficiency (FXPOI). Women with FXPOI go through menopause before the age of 40. They may also experience infertility. 

Fragile X-associated tremor/ataxia syndrome (FXTAS). This is a nervous system disorder that can happen in older adults. It can cause:

  • Tremors
  • Difficulty walking
  • Balance problems
  • Memory issues
  • Mood disorders

The symptoms of fragile X aren’t life-threatening. Your life expectancy with the condition is the same as that of anyone without it.

A lot of people with the condition are able to live successful lives on their own. About 8 in 20 women and 1 in 20 men with fragile X don’t need help with daily activities.

Depending on the severity of fragile X, people with the condition can go to school, have conversations, read books, learn new ideas, and finish other tasks by themselves.

To learn more about fragile X syndrome, join a support group. You may also reach out to an organization like the National Fragile X Foundation for advice and resources.

There, you can learn about local events and groups for people with fragile X.

There are also resources for parents. If you recently found out that your child has fragile X, this site offers many tips, videos, and firsthand experiences to help you understand how to care for them.

Fragile X syndrome is a genetic condition that causes intellectual and developmental disability. It is more severe in males than in females. People with fragile X syndrome are also more likely to develop autism.

There aren’t any risk factors for fragile X that you can control. If you have the FMR1 gene, your child could have it, too. It’s diagnosed through genetic testing. 

There’s no “cure” for fragile X syndrome, but most people with it respond well to speech, occupational, and behavioral therapy. Some adults with fragile X syndrome are able to live independently and hold a full-time job. Others need more support. Many people with fragile X syndrome go on to lead long, fulfilling lives.

What kind of mutation is fragile X syndrome?

It’s a genetic mutation. People with fragile X syndrome have changes in their FMR1 gene, which is on the X chromosome. It makes a protein called FMR that helps nerve cells talk to one another. People need this protein for their brains to develop normally. Individuals with fragile X make too little or none of it. They also have more copies than usual of a DNA segment known as CGG. In most people, this segment repeats 5 to 40 times. In people with fragile X, it repeats more than 200 times. The more times this DNA segment repeats, the more serious the symptoms are.

Is fragile X like autism?

People with fragile X have a higher incidence of autism than those without the condition. If your child has both fragile X and autism, they’re more likely to have seizures, sleep issues, more behavioral issues, and need more medications.

What are the behaviors of fragile X syndrome?

People with fragile X syndrome have many different behaviors. Some of the more challenging ones include:

  • Hand flapping
  • Being distracted easily 
  • Trouble making eye contact
  • Short attention span
  • Shyness
  • Anxiety
  • Impulsiveness

But those with fragile X have plenty of behavior strengths, too. They're great at imitation and have strong visual memories. People with fragile X can also be very social, and they like to help others.

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