Text Search

Theme Search

  • 1
  • 2
  • 3
  • 4

Klinefelter syndrome

Search for glossary terms (regular expression allowed)
Begin with Contains Exact termSounds like
All A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
Term Definition
Klinefelter syndrome

Klinefelter syndrome is a chromosomal condition that affects male sexual development. Most males with Klinefelter syndrome have one extra copy of the X chromosome in each cell. Because their testicles do not develop normally, affected males may have low levels of the hormone testosterone which can lead to breast development, reduced facial and body hair, and infertility.

Most often, Klinefelter syndrome is caused by a single extra copy of the X chromosome in all cells of the body (47, XXY). Occasionally, individuals will have the extra copy in only some of their cells (mosaic 46, XY/47,XXY) and other KS individuals will have several extra copies of the X chromosome or extra copies of both the X and Y chromosomes in all of the body's cells. Symptoms of KS can vary depending on the number of extra copies of the X chromosome. This condition is not inherited, but usually occurs as a random event during the formation of reproductive cells (eggs and sperm). An error in cell division called non-disjunction can result in reproductive cells with an abnormal number of chromosomes.

Definition from the Genetics Home Reference, US National Library of Medicine: Klinefelter syndrome

Tell us your story

We are always looking for new stories to add to this site, and are particularly keen to hear from more practitioners. Your colleagues can learn so much from how you’ve dealt with situations which involved genetics.

Contact Us

Tell us what you think

Your feedback is important in helping us to enhance this website. Please take a moment to complete the brief questionnaire.


Winners of the Association of Healthcare Communicators Best use of new media award 2009.
‘This was superb’ - Judge’s comment.


Betsi Cadwaladr Scholarship Foundation Joint Award Winners 2013.

Betsi Cadwaladr logo