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February 9, 2010
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Klinefelter Syndrome

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.



Next: What are the symptoms of the XXY condition? »

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Klinefelter Syndrome

What are birth defects?

Birth defects are structural or functional abnormalities present at birth that cause physical or mental disability. Some may be fatal.

Researchers have identified thousands of different birth defects. Currently, birth defects are the leading cause of death for infants during the first year of life.

What causes birth defects?

Birth defects have a variety of causes, such as:

Genetic problems caused when one or more genes doesn't work properly or part of a gene is missing

Problems with chromosomes, such as having an extra chromosome or missing part of a chromosome

Environmental factors that a woman is exposed to during pregnancy, such as rubella or German measles while pregnant, or using drugs or alcohol during pregnancy.

What are the different types of birth defects?

There are two main types of birth defects: structural and functio...

Read the Birth Defects article »











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