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A to Z: Klinefelter Syndrome

May also be called: XXY Condition; XXY Syndrome


More to Know

Genetic material, or DNA, is contained in tiny string-like structures called chromosomes that are found inside the body's cells. A person's physical gender (whether they have male or female sex organs) 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 Klinefelter 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 Klinefelter syndrome is present at birth and can't be changed. But medical and educational treatments and various types of therapy (physical, speech, behavioral, mental health, and occupational) can help boys have more normal puberty and physical development, keep pace in school, and overcome problems with shyness and social development.

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