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Eight healthy babies have been born following mitochondrial transfer, which creates “three-parent” embryos, in the world’s first clinical assessment of the treatment developed to reduce the risk of DNA diseases.
Genetic defects in mitochondrial DNA affect about one baby in 5,000, leading to a wide range of medical problems from muscle atrophy to heart failure and brain disease.
“Mitochondrial disease can have a devastating impact on families,” said Sir Doug Turnbull, one of the Newcastle team of scientists who led the trial. “Today’s news offers fresh hope to many more women at risk of passing on this condition who now have the chance to have children growing up without this terrible disease.”
The long-awaited results, published in the New England Journal of Medicine on Wednesday, were acclaimed as a landmark in genetic medicine by global experts in reproductive health.
Four girls and four boys, including a pair of identical twins, were born to seven women at high risk of transmitting disease-causing mutations in their mitochondria — microscopic power packs that provide cells with biochemical energy.
The infants, who range in age from a few weeks to more than two years, have developed normally, showing no signs of inherited disease.
Newcastle University was licensed in 2017 to carry out the trial of mitochondrial transfer with funding from the NHS and Wellcome Trust, after an intense debate over the ethics and medical implications of the technique.
Each infant born from the procedure carries DNA from a man and two women. It involves transferring the nucleus from the fertilised egg of a woman carrying harmful mitochondrial mutations into a donated egg from which the nucleus has been removed.
For some carriers this is the only option because conventional IVF does not produce enough healthy embryos to use after pre-implantation diagnosis.
The researchers consistently reject the popular term “three-parent babies”, said Turnbull, “but it doesn’t make a scrap of difference.”
Mitochondria have their own genes, separate from the main genome located in the cell’s nucleus.
The mitochondria derived from the egg donor have just 13 genes. These are essential for health but are vastly outnumbered by 20,000 or so genes in the cell’s nucleus, which determine our individual human characteristics.
The trial, which set out to treat 125 women over five years, has proceeded more slowly than had been planned in 2017 owing to unexpected challenges, from donor availability to technical details of the IVF procedure.
“For many affected families it is the first real hope of breaking the cycle of this inherited condition,” said Liz Curtis, founder of the mitochondrial disease charity Lily Foundation.
The Newcastle team is working to improve the efficiency of the technique — the eight live births came from 22 women undergoing mitochondrial transfer — and make it more “refined and gentle” so that frozen donor eggs can be used, said Mary Herbert, professor of reproductive biology.
Australia is the only other country apart from the UK where mitochondrial transfer is legal, said Herbert, who also works at Monash University in Melbourne.
“I hope these results will be reassuring for the regulators [in Australia],” she said. “I believe we’re on the point of getting our first license which will enable us to do pre-clinical research and training. We’re hoping to start the clinical trial in 2026.”
