Page last updated at 11:38 GMT, Friday, 24 October 2008 12:38 UK

'One-stop' embryo test revealed

An 8-cell embryo
A cell is taken from an embryo which is just a few days old for testing

A gene mapping test could tell parents-to-be if embryos are affected by almost any inherited disease, UK scientists have claimed.

The team from London's Bridge Centre say the 1,500 test could detect any of the 15,000 inherited diseases in weeks.

Current tests are either focused on a specific gene mutation, or take a lot longer to give results.

But other experts warned the fertility regulator would have to ensure there were strict limits on the test's use.

If you can screen for anything, where do you draw the line?
Dr Mark Hamilton, British Fertility Society

At the moment, clinics can test embryos before they are implanted in a woman's womb to see if they carry a specific genetic mutation, if a family is affected by a condition such as cystic fibrosis.

Another test was developed by a team at Guy's Hospital in London two years ago, which looks at genetic "fingerprint" by looking at a whole DNA of a cell.

But the claims for this new technique, called karyomapping which analyses chromosomes, is that it is a universal 'one size fits all' test.

Mapping patterns

A single-cell is taken from an eight-day-old embryo, created using IVF.

DNA samples are then taken from the parents - and their parents.

Usually, another member of the family, most likely a child affected by the relevant condition, also provides a sample.

All those family members' DNA is then compared, looking at 300,000 specific DNA markers, allowing scientists create a map of the family's genetics.

This means they can, for example, identify if there is a block of DNA which has been passed on by the paternal grandfather to an affected child and if it is also present in the embryo - because the markers will be the same for all three.

For example, the gene for cystic fibrosis lies on chromosome 7. If the paternal grandfather was a carrier, and the embryo has inherited a section of DNA at that particular position, the embryo will have the faulty gene.

The same check can be carried out across all chromosomes to allow screening for multiple genes.

'Preventing suffering'

Professor Alan Handyside, who has developed the test, told the BBC: "The current tests can only identify a small number of defects."

"One of the main things for patients is that, quite often, there isn't a test for their particular condition. This is a single test - a universal method."

He said the test could also be used, more controversially, to detect a genetic profile which showed a susceptibility to conditions such as heart disease or cancer.

The test is currently being trialled at the Bridge Centre, but is being used alongside conventional pre-implantation genetic testing so doctors can check the results.

Once Professor Handyside has enough data he will need to apply to the fertility regulator, the Human Fertility and Embryology Authority, for a licence to use the test.

An HFEA spokeswoman said its licensing committee would be able to set conditions on what it could be used for.

Dr Mark Hamilton, chairman of the British Fertility Society, said: "The effectiveness and efficiency of the procedure is quite exciting, and the fact it's quicker means it could be helpful to couples at risk of inherited diseases - and that in itself is significant.

"We can currently test for several hundred conditions, but the claim is that the spectrum of conditions which could be screened for is enormous

"But obviously, the ethical question is, if you can screen for anything, where do you draw the line?"




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