New embryo test to screen for 6,000 diseases
Ian Sample in Prague
Monday June 19, 2006
Guardian
http://www.guardian.co.uk/print/0,,329508103-117700,00.html
British fertility specialists have developed a powerful new way to
test embryos for inherited diseases, offering hundreds of couples
their first realistic chance of having healthy children. The procedure
has been hailed as a big advance, boosting the number of diseases
clinics can test for from about 200 to nearly 6,000.
It will allow doctors to test for the first time a vast array of
inherited diseases for which the specific genetic mutation is not
known, such as Duchenne's muscular dystrophy (DMD) and some forms of
cystic fibrosis. Using the technique, doctors can examine every embryo
created for a couple through IVF, and determine whether each is
healthy and unaffected, a carrier of the disease, or destined to
develop the full-blown medical condition.
Such detailed knowledge of the genetic make-up of embryos will lead to
a radical shift in the way couples at risk of passing on certain
diseases are treated.
Some inherited conditions, known as x-linked diseases, are only passed
on to boys, but because the mutations that cause the diseases are
unknown, clinics can only screen them out by discarding every male
embryo created, even if only half are affected. The new test will
allow doctors to see which male embryos are free of the
disease-causing mutation, so fewer embryos will be wasted. In some
cases, the test will allow doctors the controversial option of asking
couples to choose the sex of the embryos that are transplanted.
"This is a big, big change in what we are going to be able to do. It
changes everything," said Professor Peter Braude of King's College
London, who was involved in the research. Specialists at Guy's
hospital in London have already used the technique to "cherry pick"
healthy embryos for seven women at risk of passing on inherited
diseases. Five of the women are pregnant and past the first trimester.
Two of the women had embryos screened for DMD, an x-linked disease
which causes crippling muscle wastage. About 100 boys are born with
DMD in Britain every day and their average life expectancy is 17
years. Two more women were at risk of passing on cystic fibrosis.
While 70% of CF is caused by a well-known genetic mutation that can
easily be picked up by screening, the women were among the 30% who
carry an unknown mutation that causes the disease. The fifth woman had
embryos tested for an unusual condition called hydatidiform mole, in
which a fertilised egg grows into a tumour.
The work is due to be revealed at the annual meeting in Prague of the
European Society of Human Reproduction and Embryology. The technique,
called preimplantation genetic haplotyping, was pioneered by Ali
al-Hellani, a Saudi Arabian fertility specialist in 2004, but has been
developed further by Pamela Renwick at Guy's hospital genetics centre
and Prof Braude, who runs a fertility centre at Kings College, London.
To test for an inherited disease, doctors remove one of eight cells
from a three-day-old embryo and extract the tiny amount of DNA from
the cell. They then use a technique called multiple displacement
amplification to replicate the DNA overnight until there is enough to
analyse. Next they take blood samples from family members, including
at least one person affected by the disease. By comparing DNA strands
of affected and unaffected family members, it is possible to identify
the region of a chromosome that is responsible for the disease. The
doctors are then able to test embryos to see which have inherited that
chromosome and which are disease-free. The treatment costs £4,100.
The Guy's team have applied to the Human Fertilisation and Embryology
Authority for licences to test for other genetic diseases, such as
fragile X- syndrome which affects one in 4,000 boys and myotonic
dystrophy, which affects upwards of one in 8,000.
Stuart Lavery, a fertility expert at Hammersmith hospital, London,
said the research would give many couples the first chance of having
healthy children. "The idea of a universal tool that can be applied
regardless of what the mutation is means many more patients will have
access to this," he said.
Case study: Linda Ball, 37, is married to Steven, 38. They live in
Daventry, Northamptonshire
Linda Ball was 13 when her brother Vaun died of Duchenne's muscular
dystrophy, an inherited muscle-wasting disease that affects boys. He
was 18.
Linda was brought up knowing she might be a carrier of the disease and
when she and her husband Steven started trying for children she
considered having a prenatal test to find out the sex of her baby. The
plan was to have an abortion if the test revealed she was carrying a
boy.
But when Linda became pregnant, she decided against the test. "I just
couldn't bring myself to have an abortion knowing there was a child
growing inside me," she said. The couple worked on the basis that by
the laws of genetic inheritance, there was a 75% chance the child
would be healthy. But Daniel was born five and half years ago and has
Duchenne's.
"Unfortunately we were in the 25%. Daniel is a wonderful little boy,
he is very intelligent, cheeky and I wouldn't swap him for anyone. But
I do blame myself sometimes for passing on this terrible disease," she
said. "There is nothing worse than knowing you are going to watch your
own child die." Linda became pregnant again some years later, and
decided to have the test, even though she knew that again, she would
not have an abortion if the baby was male. A scan revealed there was a
95% chance the baby was a girl. After a traumatic pregnancy, Linda
gave birth to Helena, who is now one. She has not yet been tested to
see if she carries the genetic mutation that causes Duchenne's, but
her parents have decided to allow her to decide whether to have the
test herself when she is 16.
Linda believes that the PGH test, which could diagnose Duchenne's from
one cell taken from a three-day-old IVF embryo before it has been
implanted, is easier to consider than a test that could lead to an
abortion. "At this point, you're talking about cells, not a foetus
that looks like a human being that you're carrying inside yourself.
It's never going to be an easy decision, but it is different," she
said.
--
"Science is the record of dead religions." -- Oscar Wilde
"There are no absolute certainties in this universe. A man must try to
whip order into a yelping pack of probabilities, and uniform success is
impossible." -- Jack Vance
"Civilization is the interval between Ice Ages." -- Will Durant.
"War is God's way of teaching Americans geography" -- Ambrose Bierce
"Progress is the increasing control of the environment by life.
--Will Durant
Joseph R. Darancette
daranc@NOSPAMverizon.net
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