In the early 1970s, researchers around the world sought to identify males having the extra chromosome by screening large numbers of newborn babies. 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.
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. 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.