Triple-X syndrome

Triple-X syndrome is a chromosomal condition which occurs only in females. A chromosome is a rod-like structure present in the nucleus of all cells in the body, with the exception of the red blood cells, which stores genetic information. Normally humans have 23 pairs of chromosomes, 46 chromosomes in total. The 23 pair, otherwise referred to as the sex chromosomes, stores genetic information which determines our sex. A male has a XY pair and a female has a XX pair of chromosomes.

A female affected by triple-X syndrome has an XX pair of chromosomes, as well as additional X chromosome, resulting in the formation of XXX. In addition to there being an extra X chromosome in every cell a mosaic form also occurs where only a percentage of body cells contain XXX while the remainder carry XX. The extent to which an individual is affected by the mosaic condition will depend upon the proportion of cells with XXX to XX throughout the body.

In this article

What are the symptoms of triple-X syndrome?

The effect of having an extra X chromosome can be very varied. Some females with triple-X syndrome show no, or very few, symptoms and are entirely ‘normal’, whilst others have a lot of typical features.

At birth, girls with triple-X syndrome are usually normally developed, although babies may be floppy (hypotonic) and weight may be slightly lower than average. Many girls have a ‘growth spurt’ up until the age of eight years and women tend to be a little taller than average.

With the ‘full blown’ condition, girls with triple-X syndrome are at risk of delays in neuromotor development, which can lead to coordination problems including both gross motor skills and/or fine motor skills. Learning ability and/or impaired social relationship skills may also be present. Behavioural problems including tantrums, shyness and emotional immaturity are rather more frequent than in girls with XX chromosomes. Delays in speech and language development are frequent.

Sexual development is normal and triple-X women are fertile though there is a slight increased risk of sex chromosome changes in their children. Individuals with triple-X syndrome have no increased risk of any diseases during childhood or in adult life.

How is triple-X syndrome diagnosed?

Because many girls with triple X syndrome are healthy and have a normal appearance, they may remain undiagnosed all their lives, or the diagnosis may be discovered while investigating for other reasons. After birth, triple X syndrome can be diagnosed by performing a chromosome analysis on a blood sample.

How is triple-X syndrome treated?

Management of the condition involves offering girls and women with appropriate support so they can develop to their full potential. There is no cure for the condition. Girls with triple-X syndrome are at risk of becoming socially isolated, particularly in the face of environmental stressors. A supportive and encouraging environment providing psychological, social and motor stimulation is, therefore, beneficial. Speech and language therapy may be beneficial.

Inheritance patterns and prenatal diagnosis

Inheritance patterns
Triple-X syndrome occurs sporadically and is not usually passed on from a mother with triple-X syndrome to her daughters. However, there is an increased risk of the condition occurring in the children of older mothers.

Prenatal diagnosis
Chorionic villus sampling at ten to 12 weeks or amniocentesis at about 16 weeks is available to all mothers with triple X syndrome, and routinely to older mothers, to confirm or exclude triple X syndrome.

What support is there for people diagnosed with triple-X syndrome and their families?

If your child is affected by a medical condition or disability, we can help. Call our freephone helpline on 0808 808 3555 to get information, support and advice. We also offer emotional support for parents via our Listening Ear service.

We have a range of parent guides on aspects of caring for a disabled child in our resource library. You may also find our Early Years Support useful, which contains links to parent carer workshops and help for families going through the diagnosis process.

We’ve listed some support groups below and you can also meet other parents online in our closed Facebook group.

Triple-X Family Network Support Group

Tel: 020 8690 9445

This is a small support network, established in 1997. It offers support to families of affected children and has information available. There are over 360 families in touch with the network.

Group details last updated October 2015.


Medical text written August 2002 by Contact a Family. Approved August 2002 by Dr R Stanhope. Last updated February 2013 by Dr R Stanhope, Consultant Paediatric Endocrinologist, The Portland Hospital, London, UK.

Although great care has been taken in the compilation and preparation of all entries to ensure accuracy, we cannot accept responsibility for any errors or omissions. Any medical information is provided is for education/information purposes and is not designed to replace medical advice by a qualified medical professional.

This entry is pending review, and certain details may no longer be up to date. Please ring our helpline or email our Rare Conditions Information Officer for more information.

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