The scientist who altered the genetics of 8 babies so that they were born without a disease they were going to suffer from

Every year, One in every 5,000 children is born with mitochondrial DNA mutations that can trigger devastating diseases . These genetic alterations, which are transmitted exclusively through the mother, affect mitochondria, cellular organelles responsible for generating the energy needed for life . When they fail, tissues with high energy demands—such as the brain, heart, or muscles—are the first to suffer.

Although decades of research have led to a better understanding of these pathologies, there is still no cure . Faced with this reality, science has turned its attention to new assisted reproduction techniques that can slow the hereditary transmission of the disease. One of the most promising is "mitochondrial donation," a pioneering in vitro fertilization technique legalized in the United Kingdom in 2015 and developed by the team at Newcastle University. Their method, known as "pronuclear transfer," seeks to prevent women who carry mitochondrial DNA mutations from passing the disease on to their children.

Thanks to this innovative technique, eight babies have been born in the United Kingdom without signs of mitochondrial disease , according to two studies published Wednesday night in The New England Journal of Medicine . Four girls and four boys, including a pair of twins, were born to seven mothers at high risk of transmitting these mutations. All of the babies were born healthy , with no detectable traces of the genetic alteration or with levels so low that they are not associated with disease.

The findings of the Newcastle team, which pioneered mitochondrial donation using fertilized human eggs , demonstrate that the new treatment is effective in reducing the risk of mitochondrial DNA diseases that would otherwise be incurable.

Pronuclear transfer is performed once the egg has been fertilized . It consists of extracting the nuclear genome —which contains the genetic information responsible for our individual characteristics, such as hair color or height—from a fertilized egg that carries a mitochondrial mutation, and transferring it to an egg donated by a healthy woman from which its own nucleus has previously been removed. The resulting embryo thus inherits the nuclear DNA of its biological parents , but its mitochondrial DNA comes almost entirely from the donated egg , which prevents the transmission of mutations responsible for serious diseases.

The woman behind the study

“The research offers cause for optimism ,” says researcher Mary Herbert , lead author of the study and one of the key figures in the development of pronuclear transfer in the United Kingdom. Her team has for years led advances in this in vitro fertilization technique designed to prevent the transmission of mitochondrial diseases from mother to child.

In children born with the new technique, mitochondrial DNA mutation levels were undetectable or well below the threshold at which clinical symptoms typically appear. However, in some cases, a small percentage of defective maternal mitochondria was detected (known as carryover ), a known limitation of mitochondrial donation technologies. This phenomenon occurs because, during the transfer of the nuclear genome to the donated egg, affected mitochondria can be carried over from the original egg.

Given this fact, Herbert clarifies that "mitochondrial donation technologies are currently considered risk-reduction treatments , not absolute prevention." "Our goal is to close that gap and move toward the complete prevention of mitochondrial diseases," he adds.

Therefore, he insists that "mitochondrial donation technologies are currently considered risk-reducing treatments due to the carryover of maternal mitochondrial DNA during the mitochondrial donation procedure. Our ongoing research aims to bridge the gap between risk reduction and prevention of mitochondrial DNA disease by addressing this problem ."

In any case, he emphasizes that " it will be essential to continue investigating the limitations of this technology if we want to further improve its results," he adds.

Beyond the clinical data, the emotional impact of the treatment is reflected in the words of the mothers themselves . “As parents, all we wanted was to give our daughter a healthy start in life . In vitro fertilization with mitochondrial donation made that possible,” says the mother of a daughter born using this technique.

She adds that “after years of uncertainty, this treatment gave us hope … and then gave us our daughter. We look at her now, full of life and potential, and we can't help but feel grateful. Science gave us a chance .”

Another mother, who gave birth to a healthy baby boy, sums up her experience this way: “We are now the proud parents of a healthy baby boy : a true success of mitochondrial replacement. This breakthrough has dispelled the cloud of fear that had plagued us for so long. Thanks to this incredible technology and the support we've received, our little family is complete. The emotional burden of mitochondrial disease has disappeared, and in its place is hope, joy, and immense gratitude .”

The results have been greeted with both enthusiasm and caution by researchers around the world. The international scientific community applauded the breakthrough in statements to the SMC as a milestone in reproductive medicine , although it emphasized the need for further research into its long-term effects .

From the Netherlands , Professor Bert Smeets described the study as "the one the community has been waiting for years," although he warns that there is still room for improvement in treatment inclusion criteria and calls for transparency regarding the low number of births achieved so far.

In Taiwan , bioethicist Lee Chung-Hsi points out that, although the technique does not alter nuclear DNA, the hereditary modification of mitochondrial DNA raises ethical questions about identity and kinship. He therefore calls for international legal frameworks to prevent abuses and inequalities between countries.

For her part, German professor Heidi Mertes emphasizes that the technique reduces the risk, but does not eliminate it entirely, and warns of a phenomenon known as "reversion," whereby defective mitochondria can multiply again after birth. Along these lines, many experts agree that PNT should only be used when there are no viable alternatives, such as preimplantation genetic diagnosis.

In Spain, scientific director Rocío Núñez Calonge and researcher Lluís Montoliu agree that the technique represents real hope for many families , but they emphasize that it is not yet regulated in our country. "We should allow it under strict conditions and with trained professionals," Montoliu argues.

Despite the nuances, the international consensus is clear: this is a significant advance that opens a new avenue for preventing devastating diseases, although its application must be accompanied by caution, clinical monitoring, and a thorough ethical debate.