Klinefelter Syndrome (XXY)

Klinefelter syndrome affects between 1 in 500 to 1 in 1,000 boys, according to the National Institutes of Health. It is a sex chromosome abnormality. (Read about "Genetics") Klinefelter Syndrome is defined by a set of characteristics and symptoms in men. According to the National Institute of Child Health and Human Development (NICHD), they include:

• enlarged breasts
• sparse facial and body hair
• a rounded body type
• small testes
• an inability to produce sperm

In the late 1950s, researchers discovered that Klinefelter syndrome was caused by an extra sex chromosome, XXY instead of the usual male arrangement, XY. In the early 1970s, studies were sponsored by NICHD to check 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. (Read about "Birth Defects") Although the syndrome's cause (i.e. an extra sex chromosome) is widespread, the syndrome itself (i.e. the set of symptoms and characteristics that may result from having the extra chromosome) is uncommon. Many men live out their lives without ever suspecting that they have an additional chromosome.

For this reason, the term "Klinefelter syndrome" has fallen out of favor with medical researchers. Most prefer to describe men and boys having the extra chromosome as "XXY males."

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.

NICHD says 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.

A far more serious symptom, however, is one that is not always readily apparent. 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, NICHD says the majority tend to have some degree of difficulty with language throughout their lives.

The National Institute of Child Health and Human Development (NICHD) says by adulthood, XXY males look similar to males without the condition, although they are often taller. They are also more likely than other men to have certain health problems, such as autoimmune disorders, breast cancer, vein diseases, osteoporosis and tooth decay. (Read about "The Immune System" "Breast Cancer" "Osteoporosis" "Oral Health")

XXY males can have normal sex lives, but they usually make little or no sperm. Between 95 percent and 99 percent of XXY males are infertile because their bodies don't make enough sperm. (Read about "Infertility")