Fragile X syndrome
Fragile X syndrome (FXS) is a genetic condition that affects learning, communication and behaviour. It is the most common inherited cause of intellectual disability in boys. FXS affects both males and females, but males are usually more severely affected.
Symptoms of Fragile X syndrome
People with Fragile X syndrome can experience a wide range of symptoms. These can vary from mild to more severe.
Issues with growth, development and learning include:
Learning and development
Issues with growth, development and learning include:
- difficulties with learning, which are usually more noticeable in males
- delays in speech and language development
- challenges with understanding non-verbal cues, such as facial expressions or body language
Behaviour
Common behavioural features include:
- short attention span or difficulty staying focused
- impulsiveness, restlessness or being easily distracted
- anxiety or shyness, especially in social situations
- behaviours similar to autism spectrum disorder, such as avoiding eye contact or preferring routines
Physical features
Not everyone will have noticeable physical features (may only be present in older children).
Those that do may have:
- a long, narrow face, or larger ears or jaw
- flexible joints or low muscle tone (hypotonia)
- flat feet or other connective tissue differences
- enlarged testicles after puberty in males (macroorchidism)
Causes of Fragile X syndrome
Fragile X syndrome is caused by a change in a gene called FMR1, found on the X chromosome.
Because it is linked to the X chromosome, males often have more noticeable symptoms than females.
The condition is inherited, which means it can be passed down in families.
Some people carry a gene change without having Fragile X syndrome themselves. These individuals are called premutation carriers and may be more common in the population.
Screening and testing for Fragile X syndrome
Fragile X cannot be diagnosed by appearance or behaviour alone.
A genetic blood test is needed to confirm the diagnosis or identify someone as a carrier.
You may be offered a test if:
- a child has developmental delay
- a close relative has Fragile X syndrome or is known to be a carrier
- you are planning a pregnancy and concerned about family risk
Treatment and support
There is no cure for Fragile X syndrome, but support can help with learning, communication and daily life.
Management of children with Fragile X syndrome is complex and should be delivered by a multidisciplinary team.
This may include:
- speech and language therapy
- behavioural or emotional support
- educational support in school
- physiotherapy or occupational therapy
- medication for symptoms such as anxiety or ADHD, if recommended by a specialist
People with Fragile X may also be monitored for related health conditions, such as epilepsy or connective tissue problems.
With the right support, many people with Fragile X syndrome lead active, fulfilling lives.
Where to get help
Health services
If you are concerned about Fragile X syndrome, speak to your GP, midwife, or health visitor. They can advise on assessment, testing, and support services.
Support organisations
Northern Ireland Rare Disease Partnership (NIRDP) offers support for individuals, family members, carers, friends and health care professionals living or working with a rare condition in Northern Ireland.
Fragile X Society (UK) offers information and support for families.
Mencap offers intellectual disability advice and support.
Genetic Alliance UK is an alliance of over 220 organisations, charities and support groups working together to improve the lives of everyone in the UK living with genetic, rare and undiagnosed conditions.
Online resources
RARDTAC– Queen's University Belfast’s rare disease focus group raises awareness and supports rare diseases throughout all communities.
Orphanet gathers and improves knowledge on rare diseases to improve the diagnosis, care and treatment of patients with rare diseases.
Caring with Rare is a resource for rare disease carers.