[an error occurred while processing this directive]
BBC News
watch One-Minute World News
Last Updated: Monday, 19 June 2006, 09:29 GMT 10:29 UK
Q&A: Embryo test
Embryo test guide: pre-implantation genetic haplotyping

UK scientists have developed a new embryo test which gives IVF couples at risk of serious inherited diseases more chance of having an unaffected baby.

What has been achieved?

Researchers from the genetics unit at Guy's Hospital in London have developed a technique to screen IVF embryos for genetic disorders.

The test looks for a genetic "fingerprint" of a condition, such as cystic fibrosis or Duchenne muscular dystrophy.

At the moment, doctors use a test called pre-implantation genetic diagnosis, which involves taking a single cell from an IVF embryo and testing it for a known mutation.

The new test not confined to searching for a single mutation, researchers say. It can tell if something is wrong with an embryo without having to know what the exact fault is.

How does it work?

The new test is called pre-implantation genetic haplotyping (PGH).

It still uses one cell from an early stage embryo created through IVF. The difference is that the cell's DNA is treated in the lab to amplify it millions of times.

Lab analysis
The new test is much quicker than current techniques, researchers say

This means there is less chance of error in the results.

The team then carries out genetic checks on the mother and father - and whoever in the family already has the condition. This is usually an existing child, but could be someone else in the family.

The test looks for a number of markers - genetic clues - for whichever disease they are checking for. If a certain proportion of these are present, it tells the researchers which of each parent's chromosomes carries a fault.

Then the researchers look to see if the same patterns are present in an embryo.

How can they tell if an embryo is affected?

The test would look for something different depending on the condition a family was affected by.

For example, cystic fibrosis is a recessive disorder, which means both the mother and the father of a child have to carry a genetic fault on chromosome 7 in order for a child to be affected.

But the existing embryo test can only check for the most common of many faults. So if the other parent had on of the rarer gene faults linked to CF, it would not be picked up.

This test can see if an embryo has inherited two faulty chromosomes - which would mean it had the condition, just one - which would mean it was a carrier, or neither - which would mean it was healthy.

What will it be used for?

The team, led by Professor Peter Braude, has already used the technique, and five couples are expecting babies.

They hope it will be used to help hundreds more families who have a history of a serious genetic condition.

As well as CF, the team have used the technique to help couples at risk of having a child with Duchenne muscular dystrophy.

This is a condition which primarily affects boys, so currently, no male embryos are used, even though there is only a 50/50 chance that each is affected.

This test can identify the DMD embryos, meaning an extra 25% of embryos could be used by the couple.

Will it be used for less serious conditions?

The researchers stress they have only used it for conditions where they have a licence from the fertility watchdog the Human Fertilisation and Embryology Authority to use the traditional test.

If they wanted to extend the use of the technique, they would have to seek permission from the HFEA.

Embryo test guide: pre-implantation genetic diagnosis

How the new screening test will work

The BBC is not responsible for the content of external internet sites

Has China's housing bubble burst?
How the world's oldest clove tree defied an empire
Why Royal Ballet principal Sergei Polunin quit


Americas Africa Europe Middle East South Asia Asia Pacific