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.