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Fragile X syndrome

Key facts

  • Fragile X is the most common inherited cause of intellectual disability and the most common genetic cause of autism.
  • It is caused by a faulty gene (mutation) on one of your X chromosomes.
  • Symptoms may include speech delays, intellectual disabilities, learning difficulties, and behavioural or emotional problems.
  • Fragile X is diagnosed with a genetic test.
  • You can test your unborn baby for fragile X using prenatal testing.
  • Fragile X has no cure, but there are interventions that can help manage living with fragile X.

    • What is fragile X syndrome?

    Fragile X syndrome (Opens in new tab) is an inherited (genetic) condition (Opens in new tab) that affects around 1 in 4000 males and 1 in 6000 females. It is caused by a change (mutation) in a gene on the X chromosome that is important for healthy brain development.

    Fragile X syndrome is the most common inherited cause of intellectual disability and the most common genetic cause of autism (Opens in new tab).

    What are the symptoms of fragile X syndrome?

    Some children with fragile X have very few symptoms, while others have significant health problems. Symptoms also differ between males and females. Females tend to have less or milder symptoms than males.

    Fragile X syndrome often causes developmental problems, including:

    Physical features of fragile X include:

    Children with fragile X syndrome may also have behavioural and emotional problems including:

    What causes fragile X syndrome?

    Fragile X syndrome is caused by a genetic mutation (change) on the X chromosome — 1 of the 2 chromosomes that determine your sex at the time of conception.

    Chromosomes carry DNA (deoxyribose nucleic acid). A gene is a small section of that DNA responsible for inherited characteristics. Sometimes, the X chromosome develops a fault, causing its DNA to change.

    Fragile X syndrome occurs when a specific gene on the X chromosome mutates (changes). If the gene changes a lot, you may have a full mutation. A person with a full mutation will be born with symptoms of fragile X syndrome.

    If the gene only changes a bit, you may have what is known as a 'pre-mutation'. People with a pre-mutation can pass the faulty gene (Opens in new tab) on to their children (be carriers), but may not have any symptoms.

    Fragile X syndrome is more common and severe in males, as they have one X chromosome and one Y chromosome. Females have two X chromosomes. This means that even if females carry the fragile X mutation on one X chromosome, the other one usually functions properly.

    When should my child see a doctor?

    Speak to your doctor about testing for Fragile X syndrome if:

    • your child show signs of intellectual or learning disability and developmental delays
    • your child show signs of behavioural or emotional problems
    • you have a family history (Opens in new tab) of fragile X syndrome, intellectual disability or autism spectrum disorder.

    How is fragile X syndrome diagnosed?

    If you have a child of any age showing symptoms of fragile X syndrome, your doctor can refer them for a DNA blood test (Opens in new tab) to see if they have the condition. Having a diagnosis can help your child get the help they need.

    Fragile X syndrome is detected by a DNA test. This is usually a blood test (Opens in new tab) or saliva test.

    The test will identify the gene that causes fragile X syndrome and can tell you whether your child has a normal gene, a pre-mutation or full mutation.

    How do I know if I am a carrier for fragile X?

    You can be tested before becoming pregnant to see if you are a carrier of the gene for fragile X. Carrier testing is recommended if you:

    If you are a carrier, there is a chance that you can pass the gene on to your children. Even if you don't have a family history of fragile X, you can still have a genetic test (Opens in new tab) to find out if you are a carrier for the condition.

    If you do have a family history of fragile X syndrome or any associated disorders, the diagnostic test may be covered under Medicare (Opens in new tab).

    If you are a carrier of the fragile X gene, a genetic counsellor can help you explore ways of having a healthy baby.

    Can fragile X syndrome be detected during pregnancy?

    If you or your partner are a known carrier for fragile X, your baby can be tested during pregnancy using amniocentesis or chorionic villous sampling.

    If your baby is found to have fragile X, you can consider whether to continue with the pregnancy or think about a termination. Your doctor can refer you to a genetic counsellor who specialises in helping people in your situation. You can also call Pregnancy, Birth and Baby for advice and support.

    How is fragile X syndrome treated?

    There is no cure for fragile X but there are effective treatments (Opens in new tab) for problems your child may experience. You can help your child reach their potential by getting them help as soon as possible after diagnosis. This is called early intervention.

    A team of different specialists can work together to look after your child's educational, behavioural and medical needs. This team may also include a psychologist (Opens in new tab) to help your family work through some of the challenges involved in supporting a person with a disability. They can also help you to speak to your child's school to develop an educational plan. If needed, you may also meet with:

    Your doctor can advise you about any medicines that can help your child any behavioural and emotional challenges.

    Living with fragile X syndrome

    It can be overwhelming to receive a diagnosis of fragile X syndrome. It's a good idea to think about seeking support from family or friends as you process the diagnosis.

    Your child may have behavioural challenges and a unique style of learning. Speak to your doctor or occupational therapist about creating a learning environment best suited to your child.

    If your child is diagnosed with fragile X syndrome, you may be eligible (Opens in new tab) for support from the National Disability Insurance Scheme (NDIS) (Opens in new tab). This can help you to fund early intervention therapies for your child.

    What are the complications of fragile X syndrome?

    Children with fragile X syndrome may have additional health challenges that can affect their daily lives. Common health problems include:

    Carriers of the fragile X pre-mutation might develop health problems including:

    Can fragile X syndrome be prevented?

    If you or your partner is a fragile X carrier and you are planning a pregnancy, it's important to have genetic counselling. A genetic counsellor can tell you about your risk of having a child with fragile X syndrome.

    If you are at high risk, you may choose to use preimplantation genetic diagnosis (PGD) to avoid having a child with Fragile X syndrome. This involves using in vitro fertilisation (IVF) instead of becoming pregnant naturally. Your embryos can then be tested for the fragile X mutation, and only embryos who do not carry the mutation will be transferred back into your uterus (womb).

    Resources and support

    Raising a child with a disability is not easy, but help is available.

    For more information for people planning a pregnancy:

    Speak to a maternal child health nurse

    Call Pregnancy, Birth and Baby to speak to a maternal child health nurse on 1800 882 436 (Opens in new tab) or video call. Available 7am to midnight (AET), 7 days a week.

    Last reviewed: September 2024

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