Triple X syndrome, also called trisomy X, is a genetic disorder that affects about 1 in 1,000 females. Females normally have two X chromosomes in all cells — one X chromosome from each parent. In triple X syndrome, a female has three X chromosomes.

Many girls and women with triple X syndrome have no symptoms or only mild symptoms. In other cases, symptoms may be more pronounced — possibly including developmental delays and learning disabilities.

Treatment for triple X syndrome depends on which symptoms, if any, are present and their severity. Normal sexual development and the ability to have children are typical for most females who have triple X syndrome.


Signs and symptoms can vary greatly among girls and women with triple X syndrome. Some may experience no noticeable effect. Others may have mild symptoms. Occasionally significant symptoms may occur. If signs and symptoms do appear, they may include varying degrees of severity or any combination of these:

  • Taller than average height with especially long legs — the most typical physical feature
  • Delayed development of speech and language skills, as well as motor skills, such as sitting up and walking
  • Learning disabilities, such as difficulty with reading (dyslexia), understanding or math
  • Problems with fine and gross motor skills, memory, judgment and information processing (developmental dyspraxia)
  • Weak muscle tone (hypotonia)
  • Abnormally curved pinky fingers
  • Behavior and emotional problems
  • Vertical folds of skin that cover the inner corners of the eyes (epicanthal folds) or widely spaced eyes (hypertelorism)

Occasionally, triple X syndrome may be associated with these signs and symptoms:

  • Premature ovarian failure or ovary abnormalities
  • Infertility or menstrual irregularities
  • Early or late puberty
  • Constipation
  • Abdominal pains
  • Seizures
  • Kidney abnormalities
  • Frequent urinary tract infections
  • Flat feet
  • Abnormally shaped breastbone
  • Heart abnormalities

Generally, girls and women with triple X syndrome have intelligence in the normal range, but possibly slightly lower when compared with siblings.

When to see a doctor

If you're concerned about your daughter's development, make an appointment to talk with your family doctor or pediatrician. Your doctor can help determine the cause and suggest appropriate action.


Although triple X syndrome is genetic, it's usually not inherited — it's due to a random genetic error.

Normally, people have 46 chromosomes in each cell, organized into 23 pairs, which includes two sex chromosomes. One set of chromosomes is from the mother and the other set is from the father. These chromosomes contain genes, which carry instructions that determine everything from height to eye color.

The pair of sex chromosomes — either XX or XY — determines a child's sex. A mother can give the child only an X chromosome, but a father can pass on an X or a Y chromosome:

  • If the child receives an X chromosome from the father, the XX pair makes the child genetically a female.
  • If the child receives a Y chromosome from the father, the XY pair means the child is genetically a male.

Females with triple X syndrome have a third X chromosome from a random error in cell division. This error can happen before conception or early in the embryo's development, resulting in one of these forms of triple X syndrome:

  • Nondisjunction. In most cases, either the mother's egg cell or the father's sperm cell divides incorrectly, resulting in an extra X chromosome in the child. This random error is called nondisjunction, and all the cells in the child's body will have the extra X chromosome.
  • Mosaic. Occasionally, the extra chromosome results from an incorrect cell division caused by a random event early in the embryo's development. If this is the case, the child has a mosaic form of triple X syndrome, and only some cells have the extra X chromosome. So females with the mosaic form may have less obvious symptoms.

Triple X syndrome is also called 47,XXX syndrome because the extra X chromosome results in 47 chromosomes in each cell instead of the usual 46.


Although some females may have no or mild symptoms associated with triple X syndrome, developmental delays or learning disabilities often occur and may lead to a variety of other issues, including:

  • Work, school, social and relationship problems
  • Anxiety and other emotional problems, such as attention-deficit/hyperactivity disorder (ADHD) and autism symptoms
  • Behavior problems
  • Poor self-esteem
  • Need for additional assistance with learning, activities of daily living, school or work

Aug. 16, 2017
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