Klinefelter syndrome is a group of symptoms caused by the presence of an extra sex chromosome, XXY instead of the usual male arrangement, XY. In the early 1970s, researchers around the world sought to identify males having the extra chromosome by screening large numbers of newborn babies. One of the largest of these studies, sponsored by the National Institute of Child Health and Human Development (NICHD)[1], checked the chromosomes of more than 40,000 infants.

Based on these studies, the XXY chromosome arrangement appears to be one of the most common genetic abnormalities known, occurring as frequently as 1 in 500 to 1 in 1,000 male births. Although the syndrome's cause, an extra sex chromosome, is widespread, the syndrome itself-the set of symptoms and characteristics that may result from having the extra chromosome-is uncommon. Many men live out their lives without ever even suspecting that they have an additional chromosome. Therefore, the term Klinefelter syndrome has been largely replaced with XXY males.

No one knows what puts a couple at risk for conceiving an XXY child. Advanced maternal age increases the risk for the XXY chromosome count, but only slightly.

Symptoms and Signs

In addition to occasional breast enlargement, lack of facial and body hair, and a rounded body type, XXY males are more likely than other males to be overweight, and tend to be taller than their fathers and brothers.
A far more serious symptom is that, although not mentally retarded, most XXY males have some degree of language impairment. As children, they often learn to speak much later than do other children and may have difficulty learning to read and write. And while they eventually do learn to speak and converse normally, the majority tend to have some degree of difficulty with language throughout their lives. If untreated, this language impairment can lead to school failure and its attendant loss of self esteem.

Diagnosis and Treatment

In recent years, many XXY males have been diagnosed before birth, through amniocentesis or chorionic villus sampling (CVS).
The next most likely opportunity for diagnosis is when the child begins school. A physician may suspect a boy is an XXY male if he is delayed in learning to talk and has difficulty with reading and writing. XXY boys may also be tall and thin and somewhat passive and shy. Again, however, there are no guarantees. Some of the boys who fit this description will have the XXY chromosome count, but many others will not.
A few XXY males are diagnosed at adolescence, when excessive breast development forces them to seek medical attention. Like some chromosomally normal males, many XXY males undergo slight breast enlargement at puberty. Of these, only about a third-10 percent of XXY males in all-will develop breasts large enough to embarrass them.
The final chance for diagnosis is at adulthood, as a result of testing for infertility. At this time, an examining physician may note the undersized testes characteristic of an XXY male. In addition to infertility tests, the physician may order tests to detect increased levels of hormones known as gonadotropins, common in XXY males.

For the most part, these symptoms are treatable. Surgery, when necessary, can reduce breast size. Regular injections of the male hormone testosterone, beginning at puberty, can promote strength and facial hair growth-as well as bring about a more muscular body type.
There are also the special educational needs of many XXY males to be considered.

For further, more detailed information on this topic, please refer to the reference source for this page.

The information in this page is presented in summarised form and has been taken from the following source(s):
1. United States National Institutes of Health, National Institute of Child Health and Human Development: http://www.nichd.nih.gov/