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About Fragile X Syndrome

Fragile X Syndrome (FXS) is a genetic condition, affecting around 1 in 4000 males and 1 in 6000 females. It can cause a wide range of difficulties with learning, as well as social, language, attentional, emotional, and behavioural problems. Some may experience connective tissue issues such as difficulty breast-feeding, hypotonia, hyperflexibility, flat feet, recurrent ear infections and mitral valve prolapse. FXS is the most common inherited cause of learning disability.


In addition, approximately in 1 in 250 females and 1 in 600 males are carriers of the Fragile X pre-mutation and may develop symptoms of a Fragile X Premutation Associated Condition (FXPAC) such as FXTAS and FXPOI. Therefore, Fragile X consists of a family of genetic conditions.  


One of the Fragile X Society’s aims is to support to families through providing information and resources about these conditions. If you would like more detailed information about Fragile X Syndrome, including specific issues like behavioural or educational needs, visit our resources page. You can also get support and information by contacting our Families and Professionals Advisors.

Watch our animated film

This short (two minute) animated film, produced for Rare Disease Day (28 February each year) provides a simple introduction to Fragile X Syndrome and Fragile X premutation-associated conditions.  Watch the video here.  


Fragile X Characteristics

There are a wide range of characteristics associated with Fragile X, however an individual person may only experience some of these. You can also find out about how Fragile X Syndrome affects people by reading some of our members' family stories.


Learning Disabilities

Learning disabilities occur in almost all males with Fragile X, to differing degrees. Some males have severe learning disability, although this is rare. Because females have two X chromosomes, and usually only one of them is affected by Fragile X, the impact of the condition varies: some females appear unaffected, others have mild learning disability and some have more severe learning disability.

Behaviour & Communication

Common behavioural features include short attention span, distractibility, impulsiveness, restlessness, over activity and sensory problems. Girls with or without learning disabilities may show concentration problems and social, emotional and communication difficulties related to extreme shyness and anxiety in social situations.

Autistic-like Features

Some children and adults show autistic-like features including avoiding eye contact, anxiety in social situations, insistence on familiar routines and hand flapping or hand biting. Although many people with Fragile X relate well to others, anxiety in unfamiliar or unpredictable situations may cause them to act in this way. Up to 50% of males, and around 15% of females with FXS may receive a dual diagnosis of autism. Speech and language are usually delayed with continuing speech and communication problems. Some children and adults develop epilepsy.


Strengths associated with Fragile X include good imitation skills, visual learning and long-term memories. Those living with Fragile X are also often described as having likeable personalities, being sensitive to others’ emotions and as having a good sense of humour! 

Physical Characteristics

There are some physical features associated with Fragile X, including a long narrow face with prominent jaw bones and ears however, these are rarely obvious in young children. The lack of distinguishing features is one of the reasons that diagnosis can be delayed. You cannot tell that someone has Fragile X just based upon their appearance or behaviour therefore the only way to tell if someone has Fragile X Syndrome is to do a genetic test


Further Information on Fragile X Syndrome

Get in touch with our Families and Professional Advisors to get information tailored to you.

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