Fragile X syndrome is a rare genetic condition that can affect how a child learns, speaks, behaves and develops. Caused by a mutation in a gene on the X chromosome, it is among the most common inherited causes of intellectual disability and may also be linked to autism spectrum disorder. Here is all you need to know about the condition.

What is Fragile X syndrome?

Fragile X syndrome is a genetic condition caused by a change in the FMR1 gene on the X chromosome. This gene normally produces a protein called FMRP, which plays an important role in brain development. In people with Fragile X syndrome, the gene is altered in a way that reduces or stops the production of this protein, affecting learning, behaviour and development. The condition can affect both males and females, though males are often more severely affected. 

What are the symptoms?

Symptoms can vary widely, but children with Fragile X syndrome commonly have developmental delays, especially in speech and language, learning difficulties and intellectual disabilities. Many also have behavioural and social challenges such as anxiety, hyperactivity, impulsive behaviour, attention problems and difficulty with eye contact. 

According to the U.S. Centers for Disease Control and Prevention (CDC), some children may have features of autism spectrum disorder, while seizures can occur in a smaller proportion of cases. Certain physical features may also become more noticeable with age, including a long and narrow face, large ears, flexible fingers, flat feet and, in boys after puberty, enlarged testicles, the CDC says.

How is it diagnosed?

Fragile X syndrome is diagnosed through a genetic blood test that looks for changes in the FMR1 gene, particularly an abnormal expansion of a repeated DNA segment known as CGG repeats. Most people have fewer than 45 repeats, while those with Fragile X syndrome typically have more than 200, which switches off the gene and prevents normal production of FMRP. 

How is Fragile X syndrome inherited? 

People with a premutation usually do not have Fragile X syndrome itself, but they can pass the altered gene on to their children. According to the CDC, a woman with a premutation has a 50% chance with each pregnancy of passing on either the premutation or a full mutation to her child, while a woman with a full mutation also has a 50% chance of passing Fragile X on. A man with a premutation can pass it on to all his daughters but not to his sons. 

When should parents seek testing?

Parents may want to speak to a paediatrician about testing for Fragile X syndrome if a child has unexplained developmental delays, especially delays in speech and language, learning difficulties, intellectual disabilities or features of autism spectrum disorder. 

Any child with unexplained developmental delay, intellectual disability and/or autism spectrum disorder should receive genetic testing for Fragile X syndrome. Testing is also recommended if there is a family history of Fragile X syndrome or related conditions. 

A diagnosis can also help families understand the cause of a child’s symptoms and guide further care and counselling. 

Can Fragile X syndrome be cured?

There is no cure for Fragile X syndrome, and treatment focuses on managing symptoms and supporting development. Health agencies recommend early intervention through speech and language therapy, occupational therapy, behavioural therapy, physiotherapy and special education support, depending on the child’s needs. 

Medicines may also be used to help manage associated problems such as attention difficulties, anxiety, mood issues, aggression or seizures.

Early diagnosis and support can improve functioning, learning and quality of life for children with Fragile X syndrome and their families.