Rocío Núñez Calonge
Scientific Director of the UR International Group and Coordinator of the Ethics Group of the Spanish Fertility Society
A team from Newcastle University (UK), led by Dr. Louise A. Hyslop, has published the first clinical results of the use of mitochondrial donation to prevent the transmission of hereditary mitochondrial diseases in The New England Journal of Medicine. Thanks to this technique, eight babies have already been born, marking a milestone in reproductive medicine.
Each year, about 1 in 5,000 babies are born with mutations in mitochondrial DNA (mtDNA), which can cause devastating diseases by affecting energy-intensive organs such as the brain, heart, and muscles. These diseases, which are transmitted exclusively through the mother, are often fatal and, until now, had no cure.
The technique used, known as pronuclear transfer—legal in the United Kingdom since 2015—involves extracting the pronuclei from the fertilized egg of the surrogate mother and transferring them to a donated egg with healthy mitochondria, from which the nucleus has been previously removed. This allows the embryo to retain the nuclear DNA of the parents, but with functional mitochondria from the donor.
The results are encouraging: in six of the eight babies born, the presence of pathogenic mtDNA variants was reduced by more than 95%; in the other two, the reduction was 77% to 88%. This demonstrates that the technique is effective in reducing the transmission of these serious hereditary diseases.
However, the study also raises ethical and scientific questions. The combination of nuclear and mitochondrial DNA from different people could have long-term effects that are still unknown. For this reason, the researchers stress the need for rigorous follow-up of these children, which in this case will continue until they reach the age of five. In addition, they insist that this procedure should only be used when there are no other viable reproductive alternatives.
This breakthrough represents new hope for many families affected by mitochondrial diseases. However, it also calls for caution, transparency, and a broad ethical debate on the limits and responsibilities of genetic medicine.