Klinefelter syndrome

Klinefelter syndrome is a disorder in which male infants are born with an extra X chromosome (XXY).
Klinefelter syndrome is relatively common. Most boys with Klinefelter syndrome have normal or slightly decreased intelligence. Many have speech and reading disabilities and difficulties with planning. Most have problems with language skills. Early problems with language may lead to problems with social interactions that affect behavior, and these children often get into trouble at school. Although their physical characteristics can vary greatly, most are tall with long arms but otherwise normal in appearance.

Puberty usually occurs at the normal time, but the testes remain small. At puberty, growth of facial hair is often sparse, and the breasts may enlarge somewhat (gynecomastia). Men and boys with the syndrome are usually infertile. Men with Klinefelter syndrome develop diabetes mellitus, chronic lung disease, varicose veins, hypothyroidism, and breast cancer more often than other men.
The syndrome is usually first suspected at puberty, when most of the symptoms develop. Analysis of the chromosomes confirms the diagnosis.

Boys with Klinefelter syndrome usually benefit from speech and language therapy and eventually can do well in school. Some men benefit by taking supplemental male hormones such as testosterone. The hormones improve bone density, making fractures less likely, and stimulate development of a more masculine appearance.