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                                                                                SCIENCE, Page 81

Catching a Bad Gene In the Tiniest of Embryos


A remarkable procedure takes society into the brave new world
ofgenetic screening

By PHILIP ELMER-DEWITT - With reporting by Dick Thompson/
Washington


    Parents used to have to wait until babies were born to
find out if they had tragic birth defects. Then came two
breakthrough fetal tests: amniocentesis, which can identify
abnormalities in the 15th week of pregnancy; and chorionic
villus sampling, which can be performed as early as the tenth
week. Neither procedure is without risk, however, and when
either succeeds in pinpointing a genetic defect, it forces
would-be parents to make a terrible choice: Do they raise a
child who might have a serious congenital affliction? Or do they
suffer the torment and pain that accompanies an abortion?

    Now couples who are concerned about passing on defective
genes may be spared that agonizing dilemma, thanks to a
remarkable new procedure that allows doctors to test days-old
embryos for genetic abnormalities outside the womb. The tech
nique -- which begins with in vitro, or "test-tube,"
fertilization and then involves plucking a single cell from an
embryo the size of a grain of sand -- has already produced a
healthy baby girl for a British couple with a 1 in 4 chance of
having a child with cystic fibrosis, according to a report in
last week's New England Journal of Medicine. It is now being
used to detect several inherited ailments, including hemophilia,
Duchenne muscular dystrophy and Tay-Sachs disease.

    But the test also takes society right into the brave new
world of genetic screening, raising the specter of eugenically
minded parents throwing out embryo after embryo in search of the
"perfect" child. And while it promises to reduce the number of
abortions later in pregnancy, it is already drawing fire from
those who oppose the taking of any human life, no matter how
small. "Once you've joined the male sperm with the female egg,
it's a human being," says Robert Powell, vice president of the
National Right to Life Committee. "You're killing the very
youngest of human beings, and that decision is based on
disability."

    At the heart of the debate are the tiny four- and
eight-cell spheres that represent human life at a very early
stage -- three days after fertilization. Scientists have long
known from animal studies that cells in these pre-embryos are
totipotent (that is, capable of taking any subsequent form, from
skin to bone marrow) and more or less expendable. A 16-cell
bovine embryo can be divided into four equal groups of four
cells each, cultured for a few more days, and then redivided to
yield 16 identical cell clusters, each of which will grow into
a genetically interchangeable cow.

    Applying this know ledge to human embryos created by in
vitro fertilization, doctors at London's Hammersmith Hospital,
led by Alan Handyside and Robert Winston, perfected a technique
for drawing cells into hair-thin pipettes one at a time. Then
they teamed up with a group from Houston's Baylor College of
Medicine and Methodist Hospital who had developed a procedure
for rapidly spotting the cystic fibrosis defect in a single
strand of DNA, using the gene-cloning technique called
polymerase chain reaction. "It's like finding one typographical
error in a book 180 times the size of the Encyclopaedia
Britannica in about six hours," says Dr. Mark Hughes, director
of Baylor's Prenatal Genetics Center.

    The experiment reported last week involved an English
husband and wife who already had a child with cystic fibrosis
and were worried about having another. Doctors followed the
standard in vitro fertilization protocol, using hormones to
stimulate the production of extra eggs, which were then mixed
with sperm in a Petri dish. Two of the resulting embryos tested
positive for cystic fibrosis. The rest were O.K., and two of
them were implanted in the mother's womb. One became Chloe
O'Brien, a healthy child who will neither get cystic fibrosis
nor pass it on to her offspring.

    Scientists have identified about 5,000 inherited diseases
that could, in theory, be spotted in young embryos, including
Huntington's disease and sickle-cell anemia. But gene screening
to catch these disorders is not likely to be widely available
anytime soon -- at least in the U.S. For one thing, it requires
couples to go through in vitro fertilization, a costly ($5,000
to $13,000) procedure with a success rate hovering around 10%.
The gene-screening test adds an additional $2,000 for each in
vitro cycle, a bill the U.S. insurance industry has already
indicated it has little interest in footing. Moreover, there is
still deep resistance among some Americans to the idea of
disposing of embryos, "defective" or not. "It doesn't fit the
definition of abortion," says Sister Marian Brady, a professor
of philosophy at Catholic University in Washington. "But it's
doing the same thing."

    This is more than a philosophical debate. Under pressure
from the powerful right-to-life lobby, the U.S. government
quietly cut federal support for in vitro research in 1979 and
later backed away from several related fields, including
fetal-cell research. Although the U.S. is still a world leader
in molecular genetics, a report by the congressional Office of
Technology Assessment recently concluded that the country is now
"less than well prepared" to put its scientific findings into
clinical practice. "The U.S. government has withdrawn funding
from this field," says Britain's Handyside, who is
understandably proud of helping produce baby Chloe. "They
wouldn't be able to do this work in Houston."