Triple-X is a chromosomal condition which occurs only in females. A chromosome is a rod-like structure present in the nucleus of all body cells, with the exception of the red blood cells, which stores genetic information. Normally humans have twenty-three pairs of chromosomes, forty-six chromosomes in total. The twenty-third 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. 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 condition will depend upon the proportion of XXX to XX throughout.

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 learning difficulties, developmental delay and/or behavioural problems. Individuals may show some or all features and furthermore may be differently affected by the severity of their symptoms.  It is not possible to offer a precise prediction of the symptoms either before or even immediately after the birth of each triple-X girl.

At birth, girls with triple-X 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. In the 'full blown' condition, girls with triple-X are at risk of delays in neuromotor development, learning ability and/or impaired psychosocial adaptation. This leads to co-ordination problems including both gross motor skills and/or fine motor skills. 

Delays in speech and language development are frequent but individuals respond well to speech therapy. Behavioural problems including tantrums, shyness and emotional immaturity are rather more frequent than in girls with XX chromosomes.

Sexual development is normal and triple-X women are fertile though there is a slight increased risk of sex chromosome changes in their children and an amniocentesis test is available to confirm this. Some women have been reported to have an early menopause, however further follow-up studies are required to confirm how likely this is for the majority of triple-X women. Individuals with triple-X have no increased risk of any diseases during childhood or in adult life.

Females with triple-X 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.

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

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

This is a small support network started in 1997 offering support to families of affected children. It publishes a biannual newsletter and has information available, details on request. There are 230 families in the UK and abroad in touch with the network.

Group details last updated Junly 2004.