24 October 2012
Last updated at 17:01 GMT
By Michelle Roberts
Health editor, BBC News online
Safety studies are still needed
US scientists say a human and animal trial of a controversial new IVF treatment has yielded promising results.
The findings in Nature magazine show healthy-looking embryos can be created from a mix of three adult donors.
Human embryos were grown in the lab and some appeared normal,
while monkeys born using the same technique remained fit and well, now
aged three.
A public consultation on the ethics of using this IVF in the UK is under way.
Its findings will be reported to the health secretary in spring 2013.
The technique is designed to prevent debilitating and fatal
"mitochondrial" diseases, which are passed down only from mother to
child and which cause muscle weakness, blindness and heart failure.
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It is still a long way off ready for human use”
Prof Peter Braude
King's College London
By using two female egg donors, these DNA errors could be cancelled out, scientists believe.
Three-person IVF uses the core genetic information from
mother and father as usual, but puts it into a donor egg which contains
healthy mitochondria.
Mitochondria sit in the cystoplasm of the egg - akin to the
white of a hen's egg. They contain only a tiny fraction of our genetic
material, with the bulk that determines things like our hair and eye
colour housed in the nucleus - a speck in the yolk if you use the hen's
egg analogy.
Scientists have been studying two ways of creating three person embryos.
One way is to take the nucleus from the mother's egg and put
it into a donor egg that has healthy mitochondria and has had its own
nucleus removed. This new egg can then be fertilised with the father's
sperm.
Another way is to fertilise the mother's egg first before removing the nucleus and putting it into the donor egg.
The latest study looked at the first method.
Testing
The Oregon Health team took eggs from seven women who had volunteered to take part in the research.
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The question is which method will
work best in humans? Neither the US nor Newcastle researchers has
allowed any human embryos to be implanted - all were destroyed after
just a few days when still smaller than a pinhead.”
The scientists were able to
replace the mitochondrial DNA in 65 of the eggs and then looked to see
how well these fared over the next week or so.
The fertilisation rate afterwards was similar to the 33
control eggs that had not been manipulated, although over half had
abnormal qualities.
Those that did fertilise normally developed to blastocyst
stage - five or six days later, the point at which IVF embryos are
normally transferred into the mother's womb - at a similar rate to the
controls.
Dr Masahito Tachibana and colleagues say their research shows
that the technique can work, at least in the lab. It is still not clear
if it could lead to a healthy baby.
The scientists now want to be able to do more studies to ensure the treatment is also safe.
UK expert Prof Mary Herbert, of Newcastle University, has
also been studying three person IVF, but using the other method which
takes the nucleus out of an already fertilised egg.
She called the latest findings "encouraging" and said they
were further proof that the concept was sound, although she believes the
technique she uses will provide better results.
Review
Before either method could be used to help couples have a
healthy baby in the UK, the government would need to give its approval
and any clinic would need to obtain a license from the regulator - the
Human Fertilisation and Embryology Authority (HFEA). Similar approval
would be needed in other countries.
Last year the HFEA was asked to review the scientific
effectiveness of both techniques. That review panel decided that the two
methods might be useful in preventing mitochondrial disease, but asked
for further experiments to assess their safety.
Prof Peter Braude, Emeritus Professor of Obstetrics and
Gynaecology, King's College London, said: "It is exactly the sort of
science that the HFEA expert committee recommended needed doing, and
demonstrates further the feasibility of this technique.
"However it is still a long way off ready for human use."
He said: "Only one in five of the original eggs obtained fertilised normally and made it through to the implantation stage.
"This would mean that in order to be certain of getting
embryos that might be suitable for transfer, around 12 eggs might be
needed, not always possible in an IVF procedure."
How do you make a baby from three people?
1) Two embryos are fertilised with sperm
creating an embryo from the intended parents and another from the
donors. 2) The pronuclei, which contain genetic information, are removed
from both embryos but only the parents' is kept 3) A healthy embryo is
created by adding the parents' pronuclei to the donor embryo, which is
finally implanted into the womb
1/2
Three-person IVF trial 'success'
Step 1. Eggs from a mother with damaged mitochondria and a donor with healthy mitochondria are collected. Step 2. The majority of the genetic material is removed from both eggs. Step 3. The mother's genetic material is inserted into the donor egg, which can be fertilised by sperm.
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