Genetics and Male Infertility
The development of in vitro fertilitzation (IVF) has allowed many couples to have the families they might otherwise have been unable to create independently. At the same time, this technology has allowed researchers to study the genetic make-up of the earliest stages of embryos. These advances are providing insights into the link between genetics and infertility and how defects (mutations) in specific genes may result in male or female infertility. It is possible that many cases of unexplained infertility will one day be found to have a clear genetic basis.
What has been learned in the last two decades of assisted reproduction is that some cases of severe male factor infertility are clearly related to gene deletions, mutations or chromosomal abnormalities.
Some men with very severe male factor infertility will be found, upon testing their blood chromosomes (known as a “karyotype”) to have an extra X chromosome. That is, instead of having a 46 XY karyotype, they have a 47 XXY karyotype. This condition is known as “Klinefelter Syndrome” and can result in failure to achieve puberty or even when puberty is achieved, these men often have male infertility. Some men with Klinefelter Syndrome can father pregnancies through the use of in vitro fertilitzation (IVF) with Intra-Cytoplasmic Sperm injection (ICSI). So far, we are not seeing an increased risk of Klinefelter Syndrome or other chromosome abnormalities in the offspring achieved in these cases.
Y chromosome micro-deletions
Also discovered in recent years is that some men with very severe low sperm counts will be found to have deletions in a certain part of their Y chromosome, known as the DAZ gene. Their karyotype is normal (46 XY) but close inspection of the Y chromosome shows there are sections of the chromosome that are missing. A portion of these men will have no recoverable sperm in the ejaculate or on testicular surgery and donor sperm is the only option. With other deletions in the DAZ gene, there is a small amount of sperm present and conception with IVF-ICSI is possible. In these cases, the male offspring which will always inherit their father’s Y chromosome, will also have this deletion, and will themselves be infertile.
Single Gene mutations
A single gene mutation in the gene for Cystic Fibrosis (CF) is associated with absence of the part of the tube (the “vas deferens”) that leads from the testicle to the urethra in the penis. These men are usually carriers for the CF gene mutation and do not themselves have the disease of Cystic Fibrosis. Sperm can be recovered from the testicles in these men to be used for IVF with ICSI but it is imperative that their wife (or egg provider) be fully tested for CF mutations as well, otherwise there is significant risk of having a child with Cystic Fibrosis.
For men with sperm counts routinely in the less than 5 million total motile sperm range, testing for genetic conditions is warranted so that these men or couples can be made aware of the genetic issues and how these issues might affect their offspring.