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In a groundbreaking advance, eight healthy babies have been born in the UK using a revolutionary technique that combines DNA from three different people to prevent the inheritance of rare and often fatal genetic diseases.
It’s an innovation made possible by a 2016 change in British law. Though banned in the United States and many other countries, the technique is also permitted in Australia.
The news “marks an important milestone,” said Dr. Zev Williams, who directs the Columbia University Fertility Centre but was not involved in the work.
“Expanding the range of reproductive options will empower more couples to pursue safe and healthy pregnancies”.
Why mitochondrial diseases are so dangerous
Most of our DNA comes from the nucleus of a cell, inherited from both mother and father. But there’s also some DNA outside of the cell’s nucleus, in structures called mitochondria – tiny energy-producing structures that come only from the mother.
When mitochondrial DNA carries dangerous mutations, it can lead to severe and often untreatable conditions in children, from seizures and muscle weakness to organ failure and early death.
Screening embryos during IVF can sometimes detect these mutations – but not always. As a result of these rare and uncertain cases, scientists have been developing a pioneering workaround: replacing the mutated mitochondria with healthy ones from a donor egg.
The mother’s genetic material is extracted and inserted into a donor egg that has had its own nucleus removed, keeping the donor’s mitochondria intact but none of her traits. The resulting embryo contains DNA from three people: the mother, the father, and a third-party mitochondrial donor.
Outcomes and early results from the UK study
Researchers from Newcastle University in the UK and Monash University in Australia, writing in the New England Journal of Medicine, reported that they applied the technique to embryos from 22 women. Eight healthy babies have been born so far, and one woman remains pregnant.
One of the babies showed slightly elevated levels of abnormal mitochondria – but not high enough to cause disease, experts say. Still, doctors will continue to monitor development.
Dr. Andy Greenfield, a reproductive health expert at the University of Oxford, called the work “a triumph of scientific innovation,” and said the method of exchanging mitochondria would only be used for a small number of women for whom other ways of avoiding passing on genetic diseases, like testing embryos at an early stage, was not effective.
While the term “three-parent baby” makes headlines, the amount of donor DNA involved is tiny – less than 1 per cent of the child’s genome.
«If you had a bone marrow transplant from a donor… you will have much more DNA from another person,” noted stem cell expert Robin Lovell-Badge.
So far, 35 families in the UK have been approved to use the technique, which is closely regulated.
Critics have voiced concerns over the long-term effects of heritable genetic changes, which is partly why the US currently prohibits clinical research into such methods. Federal restrictions have blocked the FDA from even considering applications involving embryos altered in this way
But for families like Liz Curtis’, the technique offers something they never had before: hope. Her daughter Lily died of a mitochondrial disease in 2006 at just eight months old.
She said the diagnosis “turned our world upside down, and yet nobody could tell us very much about it, what it was or how it was going to affect Lily.”
Curtis later founded the Lily Foundation in her daughter’s name to raise awareness and support research into the disease, including the latest work done at Newcastle University.
“It’s super exciting for families that don’t have much hope in their lives,” Curtis said.
