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About Triple X Syndrome

By Janine Gessner ; Updated June 13, 2017

Triple X syndrome is a genetic disorder in which a girl has three X chromosomes instead of two. Triple X occurs once in every 1,000 female births. However, doctors believe many girls with Triple X go their lifetime undiagnosed. The major features of Triple X are learning, behavioral and emotional problems. Compared with other syndromes in which a person has inherited three chromosomes, such as Down syndrome or Trisomy 18, Triple X is quite mild in nature.

The Basics

Chromosomes are structures of DNA and proteins in which genes are located. Normally, a person will have 46 paired chromosomes, one set inherited from the mother and the other from the father. All chromosomes are the same in males and females except the sex chromosomes, X and Y. Women have two X chromosomes, written "46,XX," and men have an X and a Y, written "46,XY." Sometimes, a child inherits too many chromosomes. This occurs in Triple X syndrome, in which a girl has inhered an extra X chromosome, often written as "47,XXX." As a childbearing woman ages, the chance of this event occurring increases.


A genetic test that looks at the chromosomes, called a karyotype, is used to diagnose a girl with Triple X syndrome. The majority of girls are diagnosed during childhood, adolescence or later. Often, the diagnosis is a surprise to parents because this testing is often done to rule out other genetic chromosomal syndromes.


According to the European Journal of Medical Genetics, a girl with Triple X syndrome usually has a slightly lower birth weight than other females. However, growth catches up, and they often have heights greater than the 50th percentile. Language and motor milestones may be delayed. Heart defects at birth are rare, but have been reported.

Early Childhood

Taller than their classmates, girls with Triple X can have difficulties with language and struggle a bit in school--especially in the first few years. Extra educational support allows the child to catch up and stay competitive with their classmates. While their intelligence quotient (IQ) may be slightly lower than their siblings, they usually fall within the normal range. Speech problems also occur more frequently in girls with Triple X. These girls are sensitive and may have behavioral or emotional problems as well. A healthy, supportive environment with quick recognition of problems as they occur is important as these children develop.


Learning struggles may continue though adolescence. However, a study in the European Journal of Human Genetics notes that girls who had good support during infancy and childhood did well compared with girls who did not receive adequate support. Normal physical sexual development is expected in individuals with Triple X. Behavioral problems are less frequent as the child ages.


Women with Triple X syndrome are able to have children. Premature ovarian failure has been reported in some individuals with Triple X and may occur more frequently than in the general population. While it is possible a woman with Triple X may also have a daughter or son with a chromosomal abnormality, most Triple X women have children with the normal amount of chromosomes.

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