Testing for Fragile X


Fragile X is diagnosed by a DNA blood test. The discovery of the Fragile X gene in 1991 led to the development of reliable DNA tests which can be used to identify affected individuals and carriers. 

The importance of diagnosis

The importance of diagnosing is twofold.

  • Firstly, the child can receive the appropriate help with education, speech and language and behaviour. However, adults with fragile X have specific problems too – the understanding and management of these problems can be helped once a  diagnosis of fragile X is confirmed.

  • Secondly, a diagnosis has implications  for other relatives. Some may be at risk of having affected children, having specific medical conditions (read more about this through our Carriers page) and could benefit from testing and genetic counselling.






The expanded "Fragile"-appearing site can be seen at the bottom of this chromosome.

When should Fragile X testing be considered?

Fragile X Syndrome is the most common inherited cause of learning disability, and we recommend that testing for Fragile X Syndrome is considered for all people with a learning disability or developmental delay. Fragile X testing should also be considered for all with autism or autistic-like behaviours, as Fragile X is thought to underlie up to 1 in 20 cases of autism. 


In addition, there are symptoms associated with being a Fragile X carrier, meaning that Fragile X testing should be considered for women experiencing premature ovarian insufficiency or early menopause or for those (particularly men) in later life experiencing Parkinson's-like symptoms (tremor, ataxia or cognitive decline). 

Testing Procedure in the UK


Referral for a Fragile X DNA blood test is usually arranged via a medical professional, usually the family GP, or by the child's paediatrician, if he or she has one. The blood sample may be taken at a local hospital, but it will be tested at a local genetics centre.


Results of the test are usually available in 6 to 8 weeks, and no result should take more than 18 weeks. Result giving can be face to face, over the phone, or in a letter with the offer of a follow up appointment. 



This can be a very worrying time and if you would like any more information or you would like to simply  speak to one of our support workers then please Contact Us.


What happens if the result is positive?

If the result is positive then families should be offered genetics counselling from a Genetics Counsellor, or a geneticist. This does not entail lying on a couch while someone asks “and how does it feel to have Fragile X in the family?”, but is a process where information is given about the condition and families have the opportunity to ask questions.


As Fragile X is a genetically inherited condition, when one child in a family is diagnosed with Fragile X, there are implications for the parents, brothers and sisters of the child and for many other relatives. Usually, genetic centres construct a family tree and advise that information is shared with the relevant people, so that they can decide whether they wish to be tested.


In Scotland other family members may be invited to the clinic directly but some English centres require a GP referral for each patient. 


How can we help?

Do seek support and Information from us - the Family Support section of the website contains information both about the condition and about how we can help.


If the result of the test is that the adult or child is a carrier of Fragile X, then our Carriers' Support and Information section of the website contains information both about carrier issues and about how we can help.


UK Genetics Centres

The addresses and contact details for all the UK Genetics Centres can be obtained from our Families and Professionals Advisors, so please Contact Us if you need this information.


Caution : Early tests may be inaccurate

Prior to discovery of the Fragile X gene in the early nineties and the development of the FMR1 gene test, a less reliable genetic test called karotyping (looking at the gene under the microscope to look for a visible "fragile site") was conducted.  This chromosome test was not always accurate or reliable.  Therefore, we would recommend that re-testing is considered if there is any uncertainty around the diagnosis. Families who are unsure which test they had should contact their clinical genetics centre.  The Society will be able to give you contact details.