Klinefelter Syndrome

Klinefelter syndrome is a genetic disorder in which people assigned male at birth (AMAB) have an additional X chromosome in their genetic code. Most people AMAB have 46 chromosomes (packages of DNA). This includes one copy of an X chromosome and one copy of a Y chromosome (46, XY). People with Klinefelter syndrome have a total of 47 chromosomes (47, XXY).

Klinefelter syndrome is a congenital condition. That means you’re born with it. Symptoms vary significantly from person to person. You might receive a diagnosis early in life. But many people don’t even know they have the condition until adulthood, when symptoms like infertility come into play.

How common is Klinefelter syndrome?

Klinefelter syndrome is fairly common, occurring in about 1 in 600 people AMAB. But many people (some experts say 70% to 80%) likely don’t know they have this condition.