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.
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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
(91av, 22 November 1997, p 5).
Worldwide, 35,000 ICSI babies were born in 1998.