The emergence of assisted reproductive technologies, such as in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI), has been paralleled by the revolutionary advances in our understanding of genetic diseases. The development of 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 begin to study the genetic make-up of the earliest stages of embryos. These advances are providing insights into the overall link between genetics and infertility. We are also just beginning to understand how defects (mutations) in specific genes may result in male and female infertility.

IVF and ICSI

In the first 15 years of clinical application of in vitro fertilization to create successful human pregnancies, it became clear that the IVF procedure of simply placing eggs and sperm in a culture dish had its limitations in helping couples with very severe male factor infertility to conceive. If the male partner had a very low sperm concentration or motility, the sperm was very unlikely to bind and penetrate the egg. In 1992, the first successful pregnancy with Intracytoplasmic Sperm Injection, or ICSI, was announced in Brussels, Belgium. This technique, which involves the micro-injection of a single sperm into an egg, was so successful in achieving normal fertilization (about 60-70% of all injected eggs fertilized normally) that it rapidly spread to IVF laboratories around the world. The pioneers of this technique were careful to study the results of their work. They performed genetic testing on a large number of babies born after ICSI-assisted fertilization. Today, these studies and others have demonstrated that a small percentage of children conceived with ICSI may have a slightly higher risk of a specific type of chromosome abnormality known as sex chromosome aneuploidy.

Sex Chromosome Abnormalities

Each normal human being has 46 chromosomes, in 23 pairs, including a pair of "sex chromosomes." A typical male has one X and one Y chromosome (46XY karyotype) and a typical female has two X chromosomes (46XX karyotype). Each embryo receives an X chromosome from the mother and either an X or a Y chromosome from the father, via the sperm. Some individuals are born with an abnormal number of chromosomes, a condition called "aneuploidy." For example, if there are 3 sets of the non-sex chromosome 21 instead of a pair, this particular type of aneuploidy is known as Trisomy 21 or Downs syndrome. An individual may be born with an abnormal number of the sex chromosomes. These "sex chromosome aneuploidies" will have different characteristics in the offspring depending on which chromosome is abnormal. The embryo can have a missing X chromosome (45X karyotype) or an extra X or extra Y chromosome (47XXY, 47XYY, 47XXX karyotypes). Different types of abnormalities in the offspring can occur, depending on the type of aneuploidy.

The risk of a sex chromosome abnormality in the general population (natural conceptions) is about 2 in every 1000 births (0.2%). Studies reporting on the first few hundred children born after ICSI did not find any statistically significant differences between IVF-ICSI conceived babies and babies conceived naturally or through conventional IVF. However, in 1995, two studies were published that suggested there may be a slight increase in sex chromosome abnormalities in ICSI-conceived children. The most recent update from a group in Belgium combined with other studies, which in total have reported genetic results from 2083 children conceived after IVF-ICSI, report that the risk of a sex chromosome abnormality in children born after IVF with ICSI is about 7 in every 1000 births (0.7%). It is unclear if this increased risk is more likely to be seen in men with very severe sperm defects, or whether there is something about the procedure itself that may lead to this increased risk. That is, there may be something about the sperm of fathers with very low sperm counts that inherently leads to the increased risk in their children. Most of the men undergoing ICSI in Belgium are men with extremely low sperm counts, many of whom who must undergo testicular biopsy to obtain sperm for the injection process. Men with a history of proven fertility, such as men undergoing IVF-ICSI because of a prior vasectomy, may be in a different risk group. Further studies will be needed to clarify this issue.

Some important facts to keep in mind when considering the risks of sex chromosome abnormalities are:

The incidence of sex chromosome aneuploidy is increased after ICSI, but appears to be less than 1% of all ICSI-derived births.

The abnormality can vary greatly with regards to specific birth defects or abnormalities, depending on whether the fetus' chromosome constitution is 45X, 47XXY, 47XYY or 47XXX.

Sex chromosome abnormalities can be detected with pre-natal genetic testing such as amniocentesis or chorionic villus sampling. The couple can then decide whether or not to terminate the pregnancy.

Other Chromosome Abnormalities

It is possible that there is a wider association between genetic abnormalities and infertility in both men and women. Several studies have been published in which chromosome analysis (karyotyping) has been performed on both men and women entering IVF treatment. These studies have reported that the incidence of the male and female partners with infertility problems have about a 4-9% chance themselves of carrying a chromosomal abnormality, including sex chromosome abnormalities. This incidence reported in mostly small studies appears to be higher than the overall incidence of chromosomal abnormalities in the general population, which is about 0.7% of all live births. It is unclear if these abnormalities are the cause of the infertility. Considering the types of some of the abnormalities reported, there is clearly the potential for some of these to increase the risks of conceiving an abnormal embryo that will not be able to establish a normal pregnancy. The cost of performing a karyotype analysis is about $750.00 per sample (double this if both male and female partners are tested) and probably not routinely covered under insurance benefits for an infertility evaluation.

Single-gene Defects and Infertility

Some genetic defects, instead of involving an entire chromosome, affect a single gene. An example of this is the most common mutation seen in the Caucasian population: a mutation in the gene that causes the disease Cystic Fibrosis. As it turns out, men who are unaffected with CF, but carry a single copy of the gene (a "carrier" for Cystic Fibrosis), are at high risk to have a condition called "congenital absence of the vas deferens." Men with this condition do not have sperm in the ejaculate, but have abundant sperm in the epididymus and testicle, which is retrievable for IVF and ICSI. This is an example of a single-gene mutation that results in a specific type of male infertility. All men with congenital absence of the vas deferens should be tested for CF gene mutations. Their female partners need to be tested to determine whether or not the couple will be at risk to have a child with the disease.

Y-Chromosome Partial Deletions

In most cases, the cause of severe male factor infertility is unknown. However, 10-15% of men with severe male factor infertility (less than 2 million sperm per cc), when specifically tested, will be found to have a small portion of genetic material (DNA) missing from the Y chromosome. This type of single-gene mutation is associated with low sperm counts or azoospermia . It does not appear that this deletion is associated with any abnormality other than male infertility. Many men have been able to conceive with this condition through IVF with ICSI. A recent scientific presentation reported that of ten babies born to fathers with known partial Y chromosome deletions, all the male babies had the same deletion as their fathers. That is, they were also likely to be infertile. Although preliminary, it does not appear that this deletion is worse in the children . That is, male offspring do not have larger missing pieces of DNA than their fathers, indicating that the abnormality is not getting progressively worse with each subsequent generation.

Testing for Y chromosome partial deletions is available in a few specific laboratories such as Genzyme Genetics in Framingham, Massachusetts. The cost of testing through Genzyme is about $300.00. If a man is found to have this type of deletion, the couple may know in advance if their son will also be likely to have a fertility problem as an adult. It is likely that the son will then need to also undergo IVF-ICSI someday.

Genetics and Fertility 2001

With the Human Genome Project and other rapid advances in genetic technology, our ability to diagnose and understand the genetic basis of human disease and human infertility will continue to grow. It is possible that many cases of unexplained infertility will one day be found to have a clear genetic basis. The question then becomes: what will we do about what we find? Currently, we understand that there may be a slightly increased risk of sex chromosome abnormalities in ICSI babies. It is important that the medical community makes fertility patients aware of these risks. For the vast majority of couples, this knowledge has not been a deterrent to attempting to conceive with this technology. But it may mean that women may have another reason to consider prenatal genetic testing (chorionic villous sampling or amniocentesis) during pregnancy. With regards to the possibility that the infertile couple may carry a chromosomal abnormality, the current standard of care in performing an infertility evaluation does not routinely include performing a karyotype analysis on the male or female partner. Some scientists and physicians have advocated for this and it is possible that this testing may become routine in the future. With Y-chromosome deletions, many couples have chosen not to undergo testing as the results are unlikely to change the course of treatment, which is usually IVF with ICSI. But couples suffering from male infertility need to know that their sons may have infertility as well. Some couples, when tested, may choose to forego having a genetic child and choose to conceive with donor sperm.

During the next few years, we will undoubtedly see even greater advances in our knowledge about how genetic defects are related to male infertility and "unexplained" infertility. As more genes are identified that play a role in reproduction, defects in these genes will be discovered. ICSI has provided the ability to overcome some of these defects for the current generation seeking to have their own genetic children but may mean continued infertility for the next generation. Our hope is that greater understanding of these mutations will allow us to anticipate the potential consequences and to create healthy families.