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), 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.
Diagnosis and Treatment
In recent years, many XXY males have been diagnosed before birth, through
amniocentesis or chorionic villus sampling (CVS).
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.
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