New test shows promise in weeding out genetically damaged sperm

Monday, July 1st 2002, 12:00 am

By: News On 6

VIENNA, Austria (AP) _ A new method that allows fertility doctors to select genetically healthy sperm raises the possibility they will soon be able to routinely pick good sperm, giving them a better chance of success in creating test tube babies.

Chromosome defects in sperm are more common in infertile men, but are hard to identify. Most fertility clinics select which sperm to inject into the egg by checking their shape and the way they move.

``This is the first time there is a simple, noninvasive technique that can be of practical use to weed out sperm with the wrong number of chromosomes,'' said Arne Sunde, an embryo scientist from Trondheim University in Norway. ``The technique itself is so easy that it lends itself to routine work, so we can introduce it as an integral part of a fertility service.''

``This mimics nature. I can't foresee any negative effects; only positive effects,'' said Sunde, who was not connected with the research.

The test, described Monday by infertility specialist Gabor Huszar at a meeting of the European Society of Human Reproduction and Embryology in Vienna, uses the same method that nature does in determining which sperm can fertilize an egg.

As sperm matures, the sperm membrane changes and as it does it develops a receptor that recognizes the shell of the egg. That maturing process is associated with earlier normal chromosomal development.

In normal reproduction, only those sperm that develop this receptor are able to fertilize an egg.

Huszar discovered that healthy sperm also develop a receptor that recognizes a substance called hyaluronic acid, found in the female reproductive tract. He discovered that the formation of the two receptors are linked.

In infertile men, a large proportion of the sperm do not mature. Maturity is judged by correct chromosome development and the development of the receptors.

Doctors cannot tell the difference between mature and immature sperm when they are selecting a single sperm to inject into an egg.

``The embryologist just picks up the best-looking sperm and injects it in the egg, so you suddenly get a population of sperm which fertilizes that could never have fertilized before,'' said Huszar, a research professor of obstetrics and gynecology at Yale University School of Medicine.

While sperm injection has made it possible for hundreds of thousands of infertile men to become fathers, it also allows chromosome defects to get through that normally would not.

Although there is no proof, experts are concerned the defects inherited by children of infertile men could increase the risk of cancer, developmental problems or genetic-linked diseases later in life.

Huszar's invention involves fixing blobs of hyaluronic acid to a regular petri dish. Sperm are then sprinkled into the dish and they start swimming. The sperm that have developed the receptor for hyaluronic acid are drawn to the blobs, while the others swim right past.

The sperm that go to the blobs can then be taken out of the dish and injected into an egg.