Definition of Syndrome, Klinefelter

Syndrome, Klinefelter: A chromosome condition in boys and men that is usually due to their having 47 chromosomes with XXY sex chromosomes, rather than having the usual 46 chromosomes with XY sex chromosomes.

XXY is one of the most common chromosomal abnormalities. It occurs in 1 in 500 male births. Because it is so common, Klinefelter syndrome is considered one the SCVs (sex chromosome variations).

The signs of Klinefelter syndrome include small testes, insufficient production of testosterone, and infertility. XXY males are more likely than other males to show breast enlargement, lack of facial and body hair, a rounded body type, to be overweight, and be taller than their fathers and brothers.

The diagnosis can be difficult to make in early childhood. Klinefelter boys tend to have learning and/or behavioral problems more often than other boys.

In 1942 Drs. Harry F Klinefelter, EC Reifenstein, Jr and their mentor Fuller Albright at the Massachusetts General Hospital in Boston published a report about 9 men who had enlarged breasts, sparse facial and body hair, small testes, and inability to produce sperm. This combination of features has come to be recognized as Klinefelter syndrome.

For much more information, see Klinefelter syndrome.