Klinefelter Syndrome

Definition - What does Klinefelter Syndrome mean?

Klinefelter Syndrome is a genetic condition where a boy is born with an extra X chromosome, leading to male infertility. Humans ordinarily have 23 pairs of chromosomes. Two of these chromosomes are the sex chromosomes, which determine gender. Females have two X chromosomes, while males have one X and one Y chromosome (anyone with a Y chromosome is male).

A man with Klinefelter Syndrome has two or more X chromosomes along with the Y chromosome, so he has 47 or more chromosomes rather than the usual 46.

FertilitySmarts explains Klinefelter Syndrome

While Klinefelter Syndrome does have symptoms, these often go unnoticed until puberty, and sometimes are not noted until the man's fertility is assessed. Symptoms can include:

  • Small testes and penis
  • Reduced testosterone levels
  • Enlarged breasts
  • Reduced body hair
  • Often the man is taller than usual
  • Production of liettle or no sperm

Some of these symptoms can be alleviated with testosterone treatments, particularly if the condition is caught during puberty. However, this doesn't cure the underlying genetic disorder, and few or no sperm are found in the semen.

Sometimes a man with Klinefelter Syndrome has some normal cells containing one X and one Y chromosome. This is the mosaic condition, which can increase the production of sperm and the chances of paternity.

It is rare for a man with Klinefelter Syndrome to father a child without help, but assisted reproductive technology can be effective. Sperm are extracted from the testes (testicular sperm extraction, or TESE) and injected into an egg cell using intracytoplasmic sperm injection (ICSI) to produce an embryo for implantation.


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