Klinefelter syndrome
A sex-chromosome condition, usually 47,XXY, causing variable testicular dysfunction and androgen deficiency; it may present with small firm testes, tall stature, gynaecomastia, learning or psychosocial needs, delayed puberty or infertility and is often diagnosed late.
Definition
Klinefelter syndrome is a sex-chromosome condition in which a person with a Y chromosome has one or more additional X chromosomes, most commonly 47,XXY. It causes variable testicular dysfunction, androgen deficiency and impaired spermatogenesis, with possible developmental and psychosocial differences.
First principles
An additional X chromosome affects testicular function
Klinefelter syndrome usually results from an extra X chromosome, most often 47,XXY, with mosaic and higher-grade variants producing a spectrum. The extra gene dosage interferes with testicular development and spermatogenesis; testosterone production may become insufficient, particularly from puberty onward.
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