New test for detecting genetic defects in embryos

British scientists said on Monday they have developed a new rapid screening test using DNA fingerprinting to detect genetic disorders in embryos.

Instead of searching for an altered gene linked to an inherited illness, the new test looks for DNA fingerprints, or markers, near the gene.

The technique, which is being presented at a European fertility conference, will enable more couples at high risk of passing on a serious genetic illnesses to their children to ensure only healthy embryos are used in-vitro fertilization (IVF).

"Because you are not looking for the gene, which can be different in different families, these markers can be applied to lots of families," said Alison Lashwood of Guy and St Thomas' NHS Foundation Trust in London, England where the test was developed.

"It can be offered to more couples and also it is a more reliable test," she added.

So far the test has been used on seven women, five of whom are now pregnant. They were tested for cystic fibrosis, a common inherited disease that affects the lungs and digestive system, and Duchenne muscular dystrophy, a degenerative muscle disorder in males.

Lashwood said the test, known as pre-implantation genetic haplotyping (PGH), combines elements of existing screening methods. A haplotype is a panel of markers.

Women tested for the cystic fibrosis mutation with PGH had a one in four chance of having a child with the illness. The others had a one in two chance of having a son with Duchenne muscular dystrophy.

Most women having embryo screening do not suffer from a fertility problem but have an increased risk of giving birth to a child with a genetic disorder. The screening test can only be done using embryos created through IVF.

The test analyses DNA extracted from a cell from the embryo to detect signs of the genetic mutation.

"You can actually track the gene through the family without looking at the gene. You can see which embryos are affected and which are not," Lashwood explained.

The risk of misdiagnosis in most cases would be less than one percent, she added.

More than 5,500 doctors, scientists and fertility experts are attending the four-day meeting of the European Society of Human Reproduction and Embryology (ESHRE).