A to Z: XXY Syndrome

May also be called:Klinefelter Syndrome; XXY Condition

XXY syndrome, also called Klinefelter syndrome, is a fairly common genetic condition. It happens when a boy is born with an extra sex chromosome in most or all of his cells.

More to Know

Genetic material, or DNA, is contained in tiny structures called chromosomes found inside the body's cells. A person's biological sex is determined by the sex chromosomes: females have two X chromosomes, or XX; most males have one X chromosome and one Y chromosome, or XY. Males with XXY syndrome are born with cells that have an extra X chromosome, or XXY. This can cause delayed development and puberty, a smaller penis and testicles, infertility, and other symptoms.

The condition that causes XXY syndrome is present at birth and can't be changed. But educational treatments and various types of therapy (physical therapy, speech therapy, behavioral and mental health counseling, and occupational therapy) can help someone keep pace in school and overcome problems with shyness and social development.

Keep in Mind

Kids and teens with XXY syndrome sometimes have trouble fitting in with kids their own age. With early help, in adulthood most will have normal social relationships with friends, family members, coworkers, and others.

All A to Z dictionary entries are regularly reviewed by KidsHealth medical experts.