Triple X Syndrome

Triple X syndrome is a genetic condition where a person is born with an extra X chromosome. This condition only happens in people assigned female at birth (AFAB). Many people with triple X syndrome may have no symptoms and may not know they have the condition, or their symptoms could include being unusually tall and fertility issues.


What is triple X syndrome?

Triple X syndrome is a rare genetic condition that affects only people assigned female at birth (AFAB). It’s also called trisomy X syndrome or 47,XXX.

People are usually born with 46 chromosomes arranged in 23 pairs. (Chromosomes are the structures that carry your genetic information.) One copy of each chromosome in the pair comes from the egg, and the other copy in the pair comes from the sperm.

Usually, people have two sex chromosomes. Males have one X and one Y. Females have two Xs. But in triple X syndrome, all or some of your cells have three X chromosomes. If only some of your cells carry the extra X, it’s called 46,XX/47,XXX mosaicism.

If you have trisomy X, you may not notice any symptoms. Or you might be taller than your peers. You might have difficulty getting pregnant or have early menopause, but many people with this condition don’t.

How common is triple X syndrome?

The condition occurs in about 1 in 900 to 1,000 live births. This means that, in the United States, five to 10 people are born with triple X syndrome every day. It’s also likely that we don’t have good numbers for this syndrome because many people who have it never have any symptoms — so they never get tested.


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Symptoms and Causes

What are the symptoms of triple X syndrome?

There’s a lot of variation among people with triple X syndrome. You may not experience any symptoms, or your symptoms might be so mild that you don’t notice them. Or you may have certain physical characteristics — or neurological (brain-related) or medical conditions — associated with triple X syndrome.

Physical characteristics

Many people with triple X are taller than their peers. They’re also often taller than pediatricians predicted based on their parents’ heights. Other, more subtle physical attributes include:

  • Wide-spaced eyes (hypertelorism).
  • Vertical skin folds that cover the inner corners of the eyes (epicanthal folds).
  • Curved or bent little fingers (clinodactyly).
  • Poor muscle tone (hypotonia).

Neurological conditions

Some people with triple X syndrome have developmental delays or mental health conditions. These may include:

Other medical conditions

Rarely, some people with triple X syndrome may develop:

What causes triple X syndrome?

Triple X syndrome is a genetic disorder caused by the presence of a third X chromosome. Although it’s genetic, it’s not usually passed down from a parent (inherited). Most cases are caused by errors that happen when chromosomes multiply and divide during the formation of egg or sperm cells. They occur by chance (sporadic).

If your birthing parent was over 35 years old at the time of your delivery, you may have an increased risk of having triple X syndrome.


Diagnosis and Tests

How is triple X syndrome diagnosed?

It’s quite common to remain undiagnosed, especially if you don’t exhibit medical or developmental issues. If your healthcare provider suspects that you (or your child) have trisomy X syndrome, they may order genetic testing. These tests might be called karyotype or chromosome microarray.

Some people discover that they have triple X syndrome as part of testing for fertility.

If you’re pregnant, your healthcare provider may recommend prenatal genetic testing if you’re at higher risk for having a child with triple X syndrome — either because you’re older than 35 or have triple X syndrome yourself. These include tests such as noninvasive prenatal testing (NIPT), amniocentesis or chorionic villi sampling (CVS). It’s also possible that you’ll have these prenatal tests to look for some other information about the fetus and find out about triple X syndrome at that time. Even if prenatal testing suggests triple X syndrome, it’s still important to get genetic testing after the baby is born to confirm the diagnosis.

Management and Treatment

How is triple X syndrome treated?

There’s no cure for triple X syndrome. Early diagnosis and intervention can help children who might face developmental delays.

After diagnosis, your healthcare provider may order more tests, like:

Otherwise, your providers will help you manage any symptoms associated with triple X syndrome. These may include referral to:

If you have premature ovarian failure, your provider will discuss the pros and cons of estrogen therapy.



Can triple X syndrome be prevented?

There’s currently no way to prevent triple X syndrome. If you’re at higher risk of having a baby with triple X syndrome, talk with your healthcare provider about genetic counseling and prenatal genetic testing.

Outlook / Prognosis

What is the outlook for people with triple X syndrome?

For many people, triple X syndrome doesn’t have a huge impact on their lives. In general, early diagnosis and intervention can help to reduce the impact of developmental delays. Children should have regular medical checkups and their growth and progress should be monitored. Since symptoms can vary widely, you should get a comprehensive evaluation to determine your specific needs.

What is the life expectancy of someone with triple X syndrome?

Triple X syndrome doesn’t really impact life expectancy, but some of the related conditions may. For the most part, people with triple X syndrome live as long as those with two X chromosomes.

Additional Common Questions

Is triple X syndrome a disability?

No, triple X syndrome isn’t a disability on its own. But some of the conditions associated with triple X syndrome may limit your capacity to get and keep a job. If this happens to you or someone you love, you can try to get Social Security Disability benefits.

How does triple X syndrome affect the brain?

Since triple X syndrome is rare, we don’t have that many large studies that look at the brain in people with the condition. There’s a small study of 35 children with trisomy X. The researchers found that their brains were smaller than those of typical kids of the same age and sex. The brain areas most affected were those involved in language and executive function. Anxiety was the most common mental health condition, affecting 40% of the kids with triple X syndrome. But more, larger studies are needed to confirm these findings.

A note from Cleveland Clinic

Maybe your child has low self-esteem and struggles to make friends. Or maybe you’ve been trying to get pregnant for a long time and it’s just not working. Even if you’ve always felt a little different than your peers, getting diagnosed with a genetic condition is a lot to wrap your head around. Sometimes a diagnosis can feel affirming, like, “there’s a reason why it’s always been like this.” And other times, it can be scary or just feel very final. Either way, a diagnosis is information you didn’t have before and it’s going to take some time to process. Talk with your child’s healthcare provider as you think about when to tell them about their diagnosis. They can help also connect you to support groups and other resources.

Medically Reviewed

Last reviewed on 08/14/2023.

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