Researchers determine genetic fingerprint of healthy sperm

Thursday, September 5th 2002, 12:00 am

By: News On 6

LONDON (AP) _ Researchers have determined the genetic fingerprint of healthy human sperm _ an advance that could be a major step forward in understanding male infertility. The discovery could also lead to new types of male contraceptives.

Experts say a test that compares the genetic pattern of the sperm of infertile men with the ``benchmark'' profile of fertile sperm would show mismatches that explain the problem. Infertility in men now remains inexplicable in two-thirds of cases.

The research, outlined this week in the Lancet medical journal, was conducted by scientists at the U.S. Environmental Protection Agency, Wayne State University in Detroit and Leeds University in England.

``At the moment, at infertility clinics, we are completely blind when it comes to trying to find out why men are infertile,'' said researcher David Miller, a lecturer in reproductive biology at Leeds University. ``We rely on things like standard semen analysis (looking at the shape, size and movement of sperm) to give us some idea of what the problem is, but essentially we really are in the dark.''

The scientists analyzed thousands of millions of sperm cells from healthy, fertile men in three different samples.

The first sample contained sperm from the testicles of 19 men. In the second sample, the scientists pooled together the genetic material from the semen of nine fathers and the third sample contained the sperm from the semen of one man.

The scientists were looking for a key genetic substance called messenger RNAs in the samples. Messenger RNA is the molecule that delivers instructions from the gene to the cell's protein-making machinery

Combining the semen of nine men showed the range of messenger RNAs.

They compared the messenger RNAs among the three samples.

``There was remarkably little variation between the individual and the pooled sample. We can say that because there was a high level of correspondence between the pooled and the individual ejaculates, that we have identified a set of RNAs that are like a fingerprint for fertility,'' Miller said.

The scientists found that less than 3,000 messenger RNAs define fertile sperm.

``The argument is once you've got that, then you can look at abnormal men and look at the differences,'' said sperm expert Christopher Barratt, a professor of reproductive medicine at Birmingham University in England. ``It's a significant advance that he's come up with a fingerprint, albeit a first draft, but it's a good first draft,'' he said of Miller.

Barratt, who was not connected with the research, predicted the test could be available in clinics in about two years.

Miller said the strategy might also one day improve the safety and quality of in vitro fertilization when the problem lies with the man.

``It will help us identify men who clearly shouldn't be using their own sperm for IVF, or at least be able to tell them more accurately what the risks of using their sperm are to the offspring,'' Miller said.

The fingerprint could also be used to design contraceptives for men.

``If you found what goes wrong that makes men infertile, then you just generate the problem in a healthy man and you've got contraception. There's always a mirror image of infertility and contraception,'' Barratt said.

An example of this is the female contraceptive pill, which suppresses ovulation. Lack of ovulation is one of the causes of female infertility.