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Klinefelter Syndrome (KS)
KS describes a set of physical, language, and social development symptoms in males who have an extra X chromosome. Its main feature is infertility. Outward signs of KS can be subtle, so symptoms often are not recognized and may not be treated in a timely manner. NICHD is one of many federal agencies and NIH institutes working to understand KS, discover why it occurs, and identify and treat its symptoms.
General Information
KS describes a set of features that can occur in a male who is born with an extra X chromosome.
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The extra X chromosome results from a random error that occurs when a sperm or egg is formed.
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Researchers estimate that 1 in about 500-1,000 newborn males has one extra X chromosome. A third or fourth X chromosome in a male is much rarer.
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Many factors can affect whether a person with KS has no, mild, or severe symptoms.
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Because symptoms can be mild, many people with KS are never diagnosed or treated.
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The only way to confirm the presence of an extra chromosome is by a karyotype test.
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There is no cure, but many symptoms can be successfully treated.
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Research
NICHD conducts and supports research on Klinefelter syndrome and many disorders associated with it.
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Find a Study
NICHD conducts and supports a variety of clinical research projects related to Klinefelter syndrome.
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More Information
Find answers to other common questions about Klinefelter syndrome, such as what other conditions are associated with KS and how KS affects fertility.
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Links to websites of groups that study or provide information about Klinefelter syndrome.
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