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Testing for Fragile X


Testing for Fragile X Syndrome is carried out 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, a child diagnosed with Fragile X can receive the appropriate help with education, speech and language, behaviour, and treatment for any physical issues. Adults with Fragile X have specific problems therefore 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 and/or having specific medical conditions (see our carriers page). They could benefit from testing and genetic counselling.

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


When to Consider Fragile X Testing

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 anyone 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 primary 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, for example the family GP, or by the child's paediatrician (if he or she has one). The blood sample may be taken locally, but it will be tested at a 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 simply to speak to someone, please contact our friendly Families and Professionals Advisors.


Receiving a Positive Result


If the result is positive then families should be offered genetics counselling from a Genetics Counsellor, or a geneticist. This 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 and siblings 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. 


For further information and details on support following a positive result, visit our diagnosis page.

Help and Support


You can receive support and information from us at any time. Our help and support section has information about the condition and how we can help.


If the result of the test is that the adult or child is a carrier of Fragile X, our carriers section of the website contains information both about carrier issues and associated conditions.

UK Genetics Centres

The addresses and contact details for all UK Genetics Centres can be obtained from our Families and Professionals Advisors, so please get in touch for this information.

Early Tests May Be Inaccurate


Prior to discovery of the Fragile X gene in the early 1990s 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 a diagnosis received before the early 1990s. Families who are unsure which test they had should contact their clinical genetics centre – get in touch for help obtaining contact details.

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