For Kat Kitto, mitochondrial disease is personal. Her 14-year-old daughter Poppy is in a wheelchair, non-verbal, and fed through a tube. Her older daughter, Lily, carries the same invisible risk and could pass the disease to her children. “It’s impacted a huge part of her life,” Kitto told BBC. “We have a lovely time as she is, but there are the moments where you realize how devastating mitochondrial disease is.”

Now, for the first time, families like Kitto’s have a new source of hope.

A team of British scientists has announced the successful birth of eight babies using an experimental technique that gives a child DNA from three people. Researchers have been developing the procedure over decades to prevent the transmission of mitochondrial diseases—inherited disorders that can cause blindness, seizures, paralysis, heart failure, and death.

All eight children appear to be healthy, with no signs of the devastating mutations their mothers carry. The news, detailed in two papers published in The New England Journal of Medicine (Study 1 & Study 2) marks the world’s first large-scale success of a technique long clouded by controversy and ethical debate.

Why Some DNA Needs Replacing

Mitochondria are often called the powerhouses of the cell. But when mitochondrial DNA (separate from the chromosomes in the nucleus) is faulty, the results can be catastrophic. Children with mitochondrial disorders may suffer from seizures, blindness, heart failure, brain damage, or paralysis. Many die young. One in every 5,000 babies is born with such a disorder.

Because mitochondria are inherited exclusively from the mother, women with these mutations face harrowing choices. Adoption, egg donation, or risking the odds.

For some, those options weren’t enough.

“This treatment gave us hope—and then it gave us our baby,” said one mother in a statement shared anonymously through the Newcastle Fertility Centre. “We’re overwhelmed with gratitude.”

A Technique Decades in the Making

The procedure, known as pronuclear transfer, has been in development for over 20 years. It begins like standard IVF. The mother’s egg and the father’s sperm are used to create a fertilized embryo. But instead of allowing it to grow, scientists remove the nuclear DNA—the bulk of genetic material that determines traits like eye color and height.

That nucleus is then inserted into a donor egg, one that has healthy mitochondria but had its own nucleus removed. The resulting embryo contains the parents’ nuclear DNA and the donor’s mitochondrial DNA. It is then implanted into the mother’s uterus.

The result: a child free of mitochondrial disease, but genetically related to their three parents.

In the UK, this is legal. In fact, it’s the only country where the technique is both approved by law and offered through a national health service. The Human Fertilisation and Embryology Authority (HFEA) tightly regulates each case.

“This is an important breakthrough—a big step forward,” Professor Doug Turnbull of Newcastle University, one of the scientists who pioneered the approach, told NPR.

What the Research Shows

Among 22 women who underwent pronuclear transfer, eight gave birth to healthy children. One more pregnancy is ongoing. All babies were born free of mitochondrial disease. In five cases, researchers detected no faulty mitochondrial DNA at all. The remaining three featured only small traces (5% to 16%), well below the 80% threshold thought to cause illness.

None of the eight children showed signs of disease. One developed mild epilepsy that resolved without treatment. Another had a heart rhythm issue that was successfully treated.

“All the children are well and continue to meet their developmental milestones,” Turnbull said.

These were families that had previously watched other children suffer and die. One couple had lost multiple children. Another woman carried a variant known to cause blindness and heart failure. Thanks to mitochondrial donation, their newborns appear healthy.

Still, the researchers emphasize that long-term monitoring will continue. Some children are still only under one year old.

“We don’t know the future,” said bioethicist Françoise Baylis. “There are risks to the women who are going to be receiving the embryo and to the women who are the donor of the eggs.”

Promise, but No Panacea

Not all women are eligible for mitochondrial donation. Those with moderate levels of mutation may instead undergo preimplantation genetic testing (PGT), where embryos are screened and only those with low levels of mitochondrial mutation are implanted. In the Newcastle study, 18 babies were born using PGT.

However, PGT offers no safe embryos for women with homoplasmic variants, where all mitochondrial DNA copies are mutated. For them, pronuclear transfer is the only chance to have a genetically related child without passing on disease.

Yet even the carefully selected embryos are sometimes at risk. The Newcastle team noted that mitochondrial carryover—where a small amount of faulty DNA slips through—is still possible, and not fully understood. In rare cases, mutant mitochondria could multiply, potentially causing disease later in life.

A Careful but Controversial Future

The UK’s program is widely seen as a global model. It includes rigorous screening, counseling, and postnatal monitoring. All applications are approved individually by the HFEA.

“This is the only place in the world this could have happened,” said Turnbull. “There’s been first-class science to get us to where we are, there been legislation to allow it to move into clinical treatment, the NHS to help support it and now we’ve got eight children that seem to free of mitochondrial disease. What a wonderful result.”

Elsewhere, the procedure remains controversial. The U.S. forbids creating three-parent embryos, citing ethical and safety concerns. Some bioethicists fear it’s a step toward so-called “designer babies,” where genetic engineering is used not to cure but to enhance.

“It’s dangerous,” said Stuart Newman of New York Medical College. “Biologically dangerous. And then it’s dangerous culturally… it will blossom into a full-fledged eugenics program.”

Supporters argue mitochondrial donation is different from CRISPR and other gene-editing tools. It doesn’t modify nuclear DNA. It replaces damaged components without changing what makes someone “them.”

“This is using a method that is avoiding a serious disease,” said Robin Lovell-Badge of the Francis Crick Institute. “If you care about people’s health… then I see no reason why you should not accept these methods.”

For now, the children are growing up healthy. For their families, the births mark the end of one painful chapter and the hopeful beginning of another.

“I think this is a landmark advance. It is pioneering work,” said Dietrich Egli, a developmental biologist at Columbia University. “It is extraordinary—no question about it.”

The science isn’t finished. The debates are just beginning. But for a few families in the UK, the promise of a normal childhood is already real.