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Trisomy X
Monday, 18 August 2003
Tuesday, 17 February 2004


Cells, the building blocks of the human body, are home to the genetic information, or blueprints, that determine all of our physical characteristics. These genes are organized into chromosomes, of which there are 23 pairs. Each pair is made up of one chromosome from the mother’s egg and one from the father’s sperm. One of these pairs is very special because it determines the sex of the baby. The sex chromosome can come either in the form of an X or a Y. Girls usually inherit two X chromosomes, one from her mother’s egg and one from her father’s sperm. Boys usually inherit one X chromosome from his mother’s egg, and one Y chromosome from his father’s sperm. XXX Syndrome occurs when the mother’s egg and the father’s sperm combine, and instead of resulting in XX or XY, the baby girl inherits an extra X chromosome (XXX).


Occurs in 1/1000 live female births.

Signs and Symptoms

Trisomy X females, while often above average in height, do not usually have unusual or characteristic physical features. Rare physical findings include a relatively small head and skin folds that may cover the inner corners of the eyes (epicanthal folds). Often the presenting symptom is infertility however; the vast majority of trisomy X females undergo puberty at the expected age and are usually fertile. Many patients present with a learning disability and up to 70 percent of patients have some learning problems. These include expressive language difficulties delayed learning and motor skills and impaired psychosocial adjustment.

Possible Causes

Cells destined to become eggs or sperm have to go through a unique process called meiosis. Normal cells in the body have 46 chromosomes (23 pairs), and must divide so that when the egg and sperm combine the baby has the right amount of genetic material. This division process, the first step of meiosis, requires all of the pairs of chromosomes to line up across from each other in two parallel lines. Then the two lines separate creating two new cells, each with one copy of the chromosomal pair. In XXX syndrome, the sex chromosomes do not separate so that one of the new cells ends up with the original pair, while the other cell ends up without that genetic information. These newly divided cells eventually end up as eggs or sperm and when they recombine during fertilization the baby ends up with one extra sex chromosome (the egg contributes XX and the sperm contributes X).


There are two ways that XXX Syndrome may be diagnosed. Amniocentesis and CVS allows for genetic testing before birth. With both of these tests the genetic material of fetal cells taken from the amniotic fluid or placenta are examined. After birth, a karyotype (an analysis of the chromosomes) may be performed if a pediatrician notices unusual physical features and developmental delay. Since there are rarely any physical characteristics associated with XXX Syndrome many women remain undiagnosed.


A girl with XXX Syndrome should be treated the same way one would treat a chromosomally normal child with developmental problems. It is thought that these children may be unusually vulnerable to stress, so an encouraging and supportive environment is very important. Girls with this condition may need psychological counseling as well as academic support to avoid depression and social isolation, and overcome learning difficulties.


There is great variability among 47,XXX girls. An exact prediction concerning an individual child’s prognosis is therefore not feasible.

Connect with other parents

In the spirit of community and support, Madisons Foundation offers the unique service of connecting parents of children with rare diseases. If you would like to be connected to other parents of children with this disease, please fill out this brief form.


Triple X Syndrome
The Triple-X Syndrome site provides information for parents with XXX daughters. The links to the left provide insight into development, biological details, and various articles covering prognosis, psychosocial aspects of the syndrome, and intelligence.

Triple X Support Group
Information about an international Triple X support group.

Contact A Family
An organization providing information and support for families affected by various diseases including Triple X Syndrome. There is a nice description of the syndrome with information about available support.

Google Search for Trisomy X

References and Sources

47,XXX. What is the Prognosis? Mary G. Linden, Bruce Bender, Robert Harmon, David Mrazek, and Arthur Robinson. Pediatrics 82(4). Oct 1988.

Psychosocial Competence of Unselected Young Adults with Sex Chromosome Abnormalities. Bruce Bender, Robert Harmon, Mary Linden, Becki Bucher-bartelson, and Arthur Robinson. American Journal of Medical Genetics. 88: 200-206

1999 Intelligence and Achievement in Children With Extra X Aneuploidy. J. Rovet, C. Netley, J. Bailey, M. Keenan, and D. Stewart. American Journal of Medical Genetics. 60: 356-60. 1995