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New test for genetic diseases

Ian Sample

Offers hundreds of couples their first realistic chance of having healthy children

Prague: 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 per cent of CF is caused by a well-known genetic mutation that can easily be picked up by screening, the women were among the 30 per cent 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. —

© Guardian Newspapers Limited 2006

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