Definition of Klinefelter syndrome

Klinefelter syndrome: A chromosome condition in boys and men that is usually due to 47 chromosomes with XXY 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 an SCV (sex chromosome variation).

Klinefelter syndrome is the most common genetic cause of male infertility. However, Klinefelter syndrome often remains undiagnosed because of the variation in clinical presentation and insufficient awareness of the syndrome itself. The signs of the 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. Early recognition and hormonal treatment of the syndrome can substantially improve the quality of life and prevent serious consequences. Testosterone replacement corrects the symptoms of androgen deficiency but it does not remedy the infertility.

Men with Klinefelter syndrome need not be infertile today, because a technique called intracytoplasmic sperm injection offers the opportunity for procreation even when there are no spermatozoa in the ejaculate. Spermatozoa are extracted from testicular biopsy samples, and pregnancies and livebirths can be achieved. However, the frequency of both sex chromosome and autosomal chromosome abnormalities is higher in spermatozoa from patients with Klinefelter syndrome than in those from normal men.

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.