Triple X syndrome


Triple X syndrome is an abnormality of the chromosomes that affects about 1 in 1,000 females. Females normally have two X chromosomes, one from each parent. In triple X syndrome, a female has three X chromosomes — hence, the name.

Triple X syndrome usually results from an error in the formation of a mother’s egg cell or a father’s sperm cell. Sometimes, triple X syndrome occurs as a result of an error early in the embryo’s development.

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.

Treatment for triple X syndrome depends on which symptoms, if any, your daughter exhibits and their severity.


Most people have 46 chromosomes occurring in 22 pairs, plus two sex chromosomes, one maternal and one paternal. These chromosomes contain genes, which carry instructions that determine everything from your height to your eye color.

One of these chromosome pairs determines your sex. You receive one sex chromosome from your mother and another from your father. Your mother can give you only an X chromosome, but your father can pass on an X or a Y chromosome. If you receive an X chromosome from your father, the XX pair makes you genetically a female. If you receive a Y chromosome from your father, then your XY pair means you’re genetically a male.

Females with triple X syndrome have a third X chromosome. Although this condition is genetic, it’s typically not inherited. Instead, what usually happens is that either the mother’s egg cell or the father’s sperm cell has not formed correctly, resulting in an extra X chromosome. This random error in egg or sperm cell division is called nondisjunction.

When the cause is a malformed egg cell or sperm cell, as is usually the case, all the cells in the offspring’s body have the extra chromosome. Occasionally, the extra chromosome doesn’t appear until early in the development of the embryo. If this is the case, then the female is said to have a mosaic form of triple X syndrome.

In the mosaic form, only some of the body’s cells have the third X chromosome. Because only some cells contain the extra X chromosome, females with the mosaic form of triple X syndrome may have less severe symptoms.

Triple X syndrome is also called trisomy X, triplo X syndrome and XXX syndrome. It’s also referred to as 47,XXX syndrome because of the existence of a 47th chromosome, which is the extra X chromosome.


Triple X syndrome may not cause any signs or symptoms. If symptoms do appear, they may include:

  • Tall stature
  • Vertical skinfolds that may cover the inner corners of the eyes (epicanthal folds)
  • Delayed development of speech and language skills
  • Weak muscle tone (hypotonia)
  • Curved pinky fingers (clinodactyly)
  • Behavior and mental health problems
  • Premature ovarian failure or ovary abnormalities
  • Constipation or abdominal pains

When to see a doctor

See your daughter’s doctor if you have any concerns about your daughter’s developmental progress. Your doctor can help determine what may be the cause and suggest appropriate action.