Triple X syndrome, also called trisomy X or 47,XXX, 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 don't experience symptoms or have only mild symptoms. In others, symptoms may be more apparent — possibly including developmental delays and learning disabilities. Seizures and kidney abnormalities occur in a small number of girls and women with triple X syndrome.

Treatment for triple X syndrome depends on which symptoms, if any, are present and their severity.


Signs and symptoms can vary greatly among girls and women with triple X syndrome. Many experience no noticeable effects or have only mild symptoms.

Being taller than average height is the most typical physical feature. Most females with triple X syndrome experience normal sexual development and have the ability to become pregnant. Some girls and women with triple X syndrome have intelligence in the normal range, but possibly slightly lower when compared with siblings. Others may have intellectual disabilities and sometimes may have behavioral problems.

Occasionally significant symptoms may occur. If signs and symptoms are present, they are often variable. Signs and symptoms in girls and women with triple X syndrome may include an increased risk of:

  • 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
  • Behavioral problems, such as attention-deficit/hyperactivity disorder (ADHD) or symptoms of autism spectrum disorder
  • Psychological problems, such as anxiety and depression
  • Problems with fine and gross motor skills, memory, judgment and information processing

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

  • Vertical folds of skin that cover the inner corners of the eyes (epicanthal folds)
  • Widely spaced eyes
  • Abnormally curved pinky fingers
  • Flat feet
  • Abnormally shaped breastbone
  • Weak muscle tone (hypotonia)
  • Seizures
  • Kidney abnormalities
  • Premature ovarian failure or ovary abnormalities
  • Developmental delays

When to see a doctor

If you're concerned about your child'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, including 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. 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 mild or no symptoms associated with triple X syndrome, other girls and women experience developmental, psychological and behavioral problems that may lead to a variety of other issues, including:

  • Work, school, social and relationship problems
  • Poor self-esteem
  • Need for additional support or assistance with learning, activities of daily living, school or work

Jan. 18, 2019
  1. National Library of Medicine. Triple X syndrome. Genetics Home Reference. https://ghr.nlm.nih.gov/condition/triple-x-syndrome. Accessed Sept. 11, 2018.
  2. 47 XXX syndrome. Genetic and Rare Diseases Information Center. https://rarediseases.info.nih.gov/diseases/5672/47-xxx-syndrome. Accessed Sept. 11, 2018.
  3. Bacino CA. Sex chromosome abnormalities. https://www.uptodate.com/contents/search. Accessed Sept. 11, 2018.
  4. Wigby K, et al. Expanding the phenotype of triple X syndrome: A comparison of prenatal versus postnatal diagnosis. American Journal of Medical Genetics. Part A. 2016;170:2870.
  5. About AXYS. Association for X and Y Chromosome Variations. https://genetic.org/about/. Accessed Sept. 14, 2018.
  6. Mission and history. National Center for Learning Disabilities. https://www.ncld.org/mission-and-history. Accessed Sept. 14, 2018.
  7. Freilinger P, et al. Behavioral and psychological features in girls and women with triple-x syndrome. American Journal of Medical Genetics Part A. 2018;176:2284.
  8. Wick MJ (expert opinion). Mayo Clinic, Rochester, Minn. Dec. 19, 2018.
  9. Chromosome Disorder Outreach. https://chromodisorder.org/. Accessed Jan. 6, 2019.