INFERTILITY
Method That Allows Some Men With Cystic Fibrosis To Father A Child
Article from Cystic Fibrosis Currents Newsletter
Fertility experts from St. Louis, MO, and Brussels, Belgium, have found a way around male-factor infertility associated with cystic fibrosis (CF). Several couples with CF-related male infertility have undergone this procedure in the US, said Sherman J. Silber, MD, of the Department of Urology and Microsurgery at St. Luke's Hospital (St. Louis).
Two of four couples in which the man had symptomatic CF now have healthy non-CF babies as a result of the procedure, Dr. Silber said. The other two will repeat the process.
The procedure, microsurgical epididymal sperm aspiration (MESA), involves retrieving sperm from the epididymis and using it for in vitro fertilization. It was developed by Dr. Silber.
His research on men with congenital absence of the vas deferens, a frequent cause of infertility in CF, overturned the belief that epididymal sperm lack fertilization capacity.1 Epididymal sperm were used to fertilize the wives' oocytes, using a new in vitro fertilization technique that achieves a 70% success rate with even barely motile sperm.2
The technique, intracytoplasmic sperm injection (ICSI), was developed at the Dutch-Speaking Free University in Brussels, Belgium.2-4 Embryos were screened for the delta F508 mutation using polymerase chain reaction, and heterozygous embryos were implanted.
Obstructive azoospermia and absence of the vas deferens is the major cause of infertility in men with CF.5 Congenital bilateral absence of the vas deferens (CBAV) is also one of the most common causes of male infertility in the non-CF population. Genetic studies have shown that CBAV is associated with the most common CF mutation and represents a primarily genital form of CF with no other phenotypic manifestations of CF.
"Normally with congenital blockage there are two problems that prevent fertilization. One is that if sperm don't traverse the epididymis and vas deferens, they don't have a chance to go through a maturing mechanism which develops their motility apparatus and the membrane fusion apparatus required for fertilization. So the healthiest sperm we can retrieve from the epididymis have a low fertilization rate because they haven't gone through the maturing process of epididymal transport," Dr. Silber explained. The second problem is that there are a lot of sperm that have been around for a long time and have died of old age.
Freshest Sperm Collected, Injected
In the MESA technique, immature sperm are collected from the epididymis. "We want to get sperm that are the freshest, most recently made, so that the DNA has not deteriorated. We know for sure that they won't be mature enough to fertilize on their own, but if we inject them into the egg with the ICSI technique, the fertilization rate is 70% and the pregnancy rate is high," Dr. Silber said.
ICSI is the newest and most successful in vitro fertilization (IVF) method to be developed since IVF began in 1978.
"We'd been experimenting for 10 years with different methods of egg injection. One was just to open a hole in the hard outer shell of the egg, the zone pellucida, and hope that sperm which would otherwise be too weak to get through would get in. Well, the results of this were pretty terrible. Then for a long time we tried injecting sperm directly underneath the zone, but not penetrating the egg, with the assumption that penetrating the inner membrane of the egg would destroy it. This led to various sub-zonal insemination techniques.
"The problem there, however, was that injecting just one sperm never worked. So you might inject 5-10 sperm and get some fertilization, but in most cases more than one sperm would fertilize the egg because the selective barrier of the zone was bypassed. So that technique didn't work well either," Dr. Silber pointed out.
"Finally, it was discovered two-and-a-half years ago that if the egg is oriented so that the polar body was at a position of 12 o'clock or 6 o'clock, we could inject the egg in such a manner that we don't hit or damage it. By orienting the egg in this way and using a much more delicately pulled pipette than we had been using before, we could inject one sperm with intact DNA directly into the egg, and get normal fertilization rates," Dr. Silber said.
Techniques More Widely Available
The MESA and ICSI techniques have been performed in hundreds of infertile couples in which the male has CBAV, according to Dr. Silber. "We've tested a number of variables and the only thing that determines the pregnancy rate is the wife's age," Dr. Silber said. If the woman is under 30, the pregnancy rate is about 65% per attempt; if she is between 30 and 37, the pregnancy rate is 46% per attempt; and when she is over 38, the pregnancy rate drops to 24% per attempt. In the latter group, the live delivery rate is only 5% because there is a high miscarriage rate.
"It doesn't matter whether the sterility is related to CF or to some other cause. All we have to do to perform the technique is retrieve the sperm. This can be done with any male CF patient, or, for that matter, with men who are infertile for almost any reason," Dr. Silber said.
For couples considering this technique, genetic screening for CF should be performed on the woman. If she is a carrier of the CF gene, then preimplantation testing for CF is indicated.
"When the embryos are 3 days old, about 8 cells, we can use the same micromanipulation apparatus used in fertilization to retrieve one or two cells from the blastomere and do a PCR test with amplification of the CF gene. Within 6 to at most 8 hours we will know whether the embryos are homozygous or heterozygous for CF.
"If the embryos are homozygous, then we can freeze them and save them indefinitely - for some future date when there may be a genetic cure - if this is what the couple wants. Many couples would rather have embryos homozygous for the CF gene frozen and saved," Dr. Silber said.
The MESA/ICSI procedures were performed only by Dr. Silber and his colleagues in St. Louis and Brussels as recently as 1 year ago, but they are now performed at most major US fertility clinics as well.
"It's unbelievable. I presented a paper at the World Congress of Infertility recently and found that almost every major fertility center is working on what seemed very controversial 2 years ago, when we first developed it," Dr. Silber reported. The procedure costs approximately $10,000 and is not generally covered by health insurance. "This is a lot, but compared with other procedures available to an infertile couple, such as laparoscopy or varicocelectomy, which cost $8,000 or more and have very poor results, it's a very cost-effective treatment," Dr. Silber said.
References: 1. Silber SJ, Ord T, Balmaceda J, et al. Congenital absence of the vas deferens: the fertilizing capacity of human epididymal sperm. N Engl J Med. 1990;323:1788-1792. 2. Van Steirteghem AC, Nagy Z, Joris H, et al. High fertilization and implantation rates after intracytoplasmic sperm injection. Hum Reprod. 1993;8:1061-1066. 3. Silber SJ, Nagy Z, Liu J, et al. Conventional in vitro fertilization versus intracytoplasmic sperm injection for patients requiring microsurgical sperm aspiration. Hum Reprod. 1994;9:1705-1709. 4. Silber SJ, Van Steirteghem AC, Liu J, et al. High fertilization and pregnancy rate after intracytoplasmic sperm injection with spermatozoa obtained from testicle biopsy. Hum Reprod. 1995;10:148-152. 5. Liu J, Lissens W, Silber SJ, et al. Birth after preimplantation diagnosis of the cystic fibrosis AF508 mutation by polymerase chain reaction in human embryos resulting from intracytoplasmic sperm injection with epididymal sperm. JAMA. 1994;272:1858-1860.
