Klinefelter's syndrome

Originally Published: October 26, 2001 - Last Updated / Reviewed On: October 30, 2009
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Dear Alice,

A man I met said he has 2 X and 1 Y chromosomes — is there a name for this that I can look up information on?

Dear Reader,

Men who are born with two X chromosomes (or a genotype of XXY, instead of the more typical XY) usually develop a condition called Klinefelter's syndrome. Klinefelter's is the most common sex chromosome variation of many; it affects approximately 1 in 500 males across all ethnic and racial groups.

Because the "extra" X chromosome is a sex chromosome, most of the physical effects of Klinefelter's syndrome become apparent during puberty. Men with Klinefelter's tend to be tall and have decreased facial hair and muscle mass. They are also more likely to have breast development and very small testicles. Some of these physical differences are thought to be the result of decreased testosterone levels. Injections of synthetic testosterone can increase muscle development and bone density, giving men with Klinefelter's syndrome a more traditionally masculine appearance. However, this replenishment of testosterone cannot correct the infertility that most with Klinefelter's have as a result of the condition. Some research suggests that early (recommended by ages 11 to 13 years) testosterone replacement therapy may decrease the incidence and severity of learning disabilities that can be related to having Klinefelter's, potentially improving overall quality of life. However, research on the cognitive problems associated with Klinefelter's is still in the early stages.

Since the characteristics of XXY men can vary significantly from person to person, there is no specific time when Klinefelter's syndrome is usually identified. In fact, some XXY men may never be diagnosed at all. Among those who are diagnosed with Klinefelter's, some are identified during childhood when their parents seek treatment for speech problems and learning and/or developmental difficulties that present at school. Others are diagnosed at puberty, when they fail to develop secondary sex characteristics. Some are diagnosed in utero, when their mothers undergo amniocentesis or other pre-natal tests. And some men with few symptoms are not diagnosed until they seek medical care for infertility. Definitive diagnosis of Klinefelter's syndrome is made through laboratory analysis and chromosomal karyotyping (an examination of chromosomes) of a blood sample. A complete medical and neurological evaluation is also done, and, when necessary, boys or men with Klinefelter's are referred to a psychiatrist, psychologist, speech pathologist, and/or language therapist. With support services and the option of testosterone therapy, many men with Klinefelter's syndrome lead perfectly healthy lives.

For more information about Klinefelter's syndrome and other sex chromosome variations, check out the American Association for Klinefelter Syndrome Information and Support, the Klinefelter Syndrome and Associates, and the Developmental Disabilities Digest websites.

If you have a relationship with a man with Klinefelter's syndrome, whether friendly or romantic, you may want to consider why the person told you. Is he looking for support? How does this affect him, or you? If he is a good friend, perhaps you could ask him your questions, if you are willing to respect his right to respond with a, "butt out." Asking this question and checking out the resources above are a great way to inform yourself about this condition and learn more about the complexities of genetics and life.

Alice