A POPULAR IVF technique may increase the risk of babies being born with abnormalities such as ambiguous genitalia.
For roughly 5 per cent of men seeking fertility treatment because they have few or no sperm, the cause is a tiny mutation in the Y chromosome called a microdeletion. As long as the man still produces a few sperm, however, it is sometimes possible to inject one directly into the egg-a technique called intracytoplasmic sperm injection.
One of the reasons ICSI is controversial is that if there's a genetic reason for the man's infertility, it will be passed on to his sons. Many couples are prepared to use ICSI anyway, arguing that it will also be available to their children.
But evidence presented at a symposium at the Monash Institute of Reproduction and Development in Melbourne last week suggests that microdeletions on the Y chromosome are a precursor to more serious genetic faults. Ken McElreavey of the Pasteur Institute in Paris found that in eight men with microdeletions, Y chromosomes were missing in about 10 per cent of the cells in their bodies. In the three who had enough sperm to test, up to 18 per cent of the sperm lacked a Y chromosome.
These findings suggest that the microdeletion is a sign of a chromosomal instability that causes some cells to lose the entire Y chromosome, McElreavey says. The loss of the Y chromosome in some of a baby's cells-called genetic mosaicism-can cause either ambiguous genitalia or Turner's syndrome, or both. Women with Turner's have normal female genitals, but they are unusually short and do not go through puberty.
Another study to be published soon also indicates a problem with ICSI and the sex chromosomes. Andre Van Steirteghem of the Free University in Brussels (VUB), who originally developed ICSI, found through tests on amniotic cells that in ICSI pregnancies there are three times as many sex chromosome abnormalities, including loss of the Y chromosome. But the risk was still very low-only 10 out of almost 1600 fetuses created by ICSI had the defects.
That doesn't mean there isn't a problem, says McElreavey. Men with Y chromosome microdeletions make up just a small fraction of those using ICSI, but they might be largely responsible for offspring with Y chromosome losses. If so, then the technique may be too risky to use on them. Every fertility clinic should be checking for these microdeletions, McElreavey says. "We need much greater follow-up of these men."
ICSI has been under fire ever since it was introduced. While most studies suggest the rate of abnormal births is no higher than usual, some indicate that it's twice as high (New Scientist, 22 November 1997, p 5). Worldwide, 35,000 ICSI babies were born in 1998.
Rachel Nowak, Melbourne
New Scientist issue: 15TH December 2001
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