'One-stop' embryo test unveiled

<http://news.bbc.co.uk/2/hi/health/7688299.stm>http://news.bbc.co.uk/2/hi/health/7688299.stm

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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