What is Fragile X Syndrome?

Fragile X is the most common cause of inherited learning disability. It affects all genders, races and ethnic groups equally. About 1:4,000 boys and 1: 6,000 girls are affected. However, the incidence of carriers of the syndrome is much higher with about 1:800 males and 1:250 females being affected.


Diagnosis is by a blood test, for which people need a medical referral. For children this is usually a paediatrician, but a GP can refer if a child is not under the care of a paediatrician. Tests are carried out at regional genetic centres, which are based in larger hospitals.

The level of learning disability associated with fragile X ranges from mild to severe with most males being in the mild to moderate range. Females with fragile X are often, but not always, more mildly affected than males. As its name would suggest, fragile X is carried on the X chromosome. Females have 2 X chromosomes whilst a male has an X and a Y. A female with fragile X will have 1 clear X and 1 fragile X, and the clear X can compensate for the fragile one. The degree to which this happens is completely random and so some females will have more marked effects with others having very little and sometimes no learning disabilities. Typically, females are very shy and many, even those with less global learning issues, have problems with maths or maths-related subjects.

Speech and language

Speech and language delay/difficulties are pretty universal. Individuals may repeat what they or someone else has said and speak in short, fast bursts with up and down swings of speech.


One of the main characteristics of Fragile X is high levels of anxiety. Another major feature is a strong dislike of eye contact with individuals often turning their head, the upper part of their body or even their whole body away from the person they are talking to. Other characteristics include a liking for routine accompanied by a dislike of change; over activity, impulsiveness and poor attention; problems with sensory processing or managing the wealth of information being transmitted to the brain through the senses. Hand flapping and self-injury (commonly biting the base of the thumb or index finger) can also be features as can dislike of transition or moving from one activity or place to another. Some individuals exhibit behaviours that challenge those around them, but such behaviours are usually that individual’s communication of something they are unable to or are finding it difficult to manage.

Many of these features can be found in individuals with ASD (autism spectrum disorders) and around 20% of those with fragile X have a dual diagnosis of ASD. The key difference between individuals with fragile X who do not have this dual diagnosis and individuals with ASD is that those with fragile X have an understanding of other people’s emotions that is commensurate with their developmental age. Empathy can actually be a strong feature of many individuals with fragile X. Many also have a great sense of humour and enjoy the company of familiar people. On the other hand, individuals with fragile X can be socially anxious and this is especially evident when they are with new people or in new situations.

Physical characteristics

There are also physical characteristics associated with fragile X, although none of them are so obvious as to make it easy to spot an individual with the syndrome from their physical characteristics. It would also be rare for anyone with fragile X to have them all and they are less obvious in younger children:

  • Larger than average head with long face and large jaw
  • Large protruding ears
  • Dental over crowding
  • Hypermobile joints, general floppy muscle tone and double jointedness. This can sometimes lead to problems with learning to walk
  • Very soft skin
  • Problems with co-ordination
  • Recurrent ear infections that can lead to problems with hearing.
  • Problems with vision

It is important to add here that it would be very rare for anyone with fragile X to have all these characteristics and that fragile X does not have a monopoly on any of them.

Best practices when working with individuals with fragile X are very similar to best practices when working with children with an ASD. Individuals with fragile X have stronger visual skills and this can be key when working with them.

The Fragile X Society

The Fragile X Society was set up to support individuals with fragile X, their parents and carers plus professionals working in the field. There are 3 Families’ and Professionals’ Advisors; one covering all enquiries in Scotland; one dealing with enquiries regarding children in the rest of the UK and one dealing with all enquiries about adults in the rest of the UK.

They can all be contacted by calling 01371 875100 or emailing info@fragilex.org.uk. They will be able to give more information on fragile X if you are already caring for a child with the syndrome or are concerned that your child may have fragile X.

There is also more information on their website at www.fragilex.org.uk.

Introductory and education booklets can be downloaded at http://www.fragilex.org.uk/booklets

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