Klinefelter syndrome

[Dianne]

Klinefelter syndrome is a sex chromosome abnormality in which boys are born with two X chromosomes plus one Y (XXY).

Klinefelter syndrome occurs when a boy has one extra X chromosome.
Boys may have learning disabilities, long arms and legs, small testes, and infertility.
The diagnosis is suspected at puberty when most of the symptoms develop.
Treatment with testosterone may be of benefit to some people.

Chromosomes are structures within cells that contain DNA and many genes. A gene is a segment of deoxyribonucleic acid (DNA) and contains the code for a specific protein that functions in one or more types of cells in the body (see Genes and Chromosomes for a discussion about genetics). Genes contain instructions that determine how the body is supposed to function.
The sex chromosomes determine whether a fetus becomes male or female. A pair of X and Y chromosomes (XY) results in a male, and a pair of X and X chromosomes (XX) results in a female.
Klinefelter syndrome is the most common sex chromosome disorder and occurs in about 1 in every 500 live male births. Most boys inherit the extra X chromosome from their mother.