Klinefelter syndrome is a relatively common genetic defect in males, which often doesn't become apparent until adulthood. Basically, Klinefelter men have an extra copy of the X chromosome in each of their cells. "Normal" men have one X chromosome and one Y chromosome. A man with Klinefelter syndrome may have two or more X chromosomes along with his Y.
This affects testosterone production in the man's body as he grows up, and can impact negatively on the development of his testicles. Nearly all Klinefelter males are infertile. Many men who have this condition never exhibit any symptoms, and are completely unaware of it until they start trying to have kids.
Having said that, this lack of testosterone is obvious in some Klinefelter males, in that they may lack facial hair or have over-developed breasts. Some Klinefelter men have noticeably smaller than average testes.
In the vast majority of cases, it is not possible to help a Klinefelter man become a biological father. A very small number of men in this situation have fathered children, but only thanks to a very expensive and not-widely available fertility treatment, which we will describe in greater detail later on.
In the meantime, Klinefelter men who don't have access to such treatments should not give up on the idea of having a family. There are a number of options available to them.
Adoption is on obvious one. Even if a man can't be the biological father of his child, his partner may want the experience of being pregnant and giving birth to a baby. This can be achieved through artificial insemination or in-vitro fertilization using donor sperm.