Klinefelter Syndrome

Klinefelter syndrome facts*

Kleinfelter syndrome facts author:

  • Klinefelter syndrome, also known as the XXY condition, is a term used to describe males who have an extra X chromosome in most of their cells.
  • About one of every 500 males has an extra X chromosome, but many don't have any symptoms.
  • Symptoms depend on how many XXY cells a man has, how much testosterone is in his body, and his age when the condition is diagnosed.
  • As XXY males enter puberty, they may have a taller, less muscular body, less facial and body hair, and broader hips than other boys. As teens, XXY males may have larger breasts, weaker bones, and a lower energy level than other boys.
  • XXY adult males look similar to males without the condition, although they are often taller and may have autoimmune disorders, breast cancer, vein diseases, osteoporosis, and tooth decay.
  • XXY males can have normal sex lives, but they usually make little or no sperm and are infertile.
  • The XXY chromosome pattern cannot be changed. Treatments involve physical, speech, occupational, behavioral, mental health, and family therapists, and testosterone replacement therapy (TRT).

What is Klinefelter syndrome?

Klinefelter syndrome, also known as the XXY condition, is a term used to describe males who have an extra X chromosome in most of their cells. Instead of having the usual XY chromosome pattern that most males have, these men have an XXY pattern. Klinefelter syndrome is named after Dr. Henry Klinefelter, who first described a group of symptoms found in some men with the extra X chromosome. Even though all men with Klinefelter syndrome have the extra X chromosome, not every XXY male has all of those symptoms.

Because not every male with an XXY pattern has all the symptoms of Klinefelter syndrome, it is common to use the term XXY male to describe these men, or XXY condition to describe the symptoms.

Scientists believe the XXY condition is one of the most common chromosome abnormalities in humans. About one of every 500 males has an extra X chromosome, but many don't have any symptoms.

Medically Reviewed by a Doctor on 3/31/2014

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