Klinefelter Syndrome

What is Klinefelter Syndrome?
Klinefelter syndrome is a genetic condition occurring only in males caused by a chromosome variation that occurs before a baby is conceived.^1,2 The scientific term for the problem that occurs prior to conception and causes Klinefelter syndrome is "nondisjunction."² The term means that the chromosomes in either the egg or the sperm involved in conception did not separate properly and the baby ends up with an extra X chromosome. People without Klinefelter syndrome have a total of 46 chromosomes and those with Klinefelter syndrome have 47 chromosomes.³ Men with Klinefelter syndrome have two X chromosomes and one Y chromosome instead of the usual one X and one Y chromosome ( karyotypes).³ The standard method of describing the chromosomes of a person with Klinefelter syndrome is to write 47,XXY.³ The 47 refers to the fact there are 47 chromosomes present. The XXY indicates that a person with Klinefelter syndrome has two X chromosomes and one Y chromosome.³

Klinefelter syndrome is a relatively common condition affecting about 1 in every 600 males.³ Unlike other conditions occurring when a person is born with an extra chromosome (such as Trisomy 13,18, or 21), people with one extra X chromosome are not typically mentally retarded.³

Individuals with Klinefelter syndrome may have some learning disabilities, language delay, and/or social interaction difficulties.³ In addition, males with Klinefelter syndrome may experience some breast enlargement during puberty, may have smaller genitalia after puberty than males without Klinefelter syndrome, may have sparse facial and body hair after puberty, tend to be tall, and are infertile.^2,3 For males with Klinefelter syndrome who are diagnosed early in life, medical treatment is often available to minimize any problems associated with the condition. ³ However, because many individuals with Klinefelter syndrome appear to be no different from males without Klinefelter syndrome, they are frequently not diagnosed until adulthood when infertility is discovered. ^2,3 For further information about Klinefelter syndrome, visit health.nih.gov.

References

1. Therman E, Susman M. Human Chromosomes: Structure, Behavior, and Effects. 3rd ed. New York, NY; Springer-Verlag; 1993.
2. Nussbaum RL, McInnes RR, Willard HF. Thompson & Thompson Genetics in Medicine. 6th ed. Philadelphia, Pa: W.B. Sounders Company, 2001.
3. Robinson A, Linden M. Clinical Genetics Handbook. 2nd ed. Ann Arbor, Mi: Blackewll Scientific Publications Inc; 1993:11:109-111.

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