Eight 'three-parent babies' have been born in the UK with genes contributed by three parents. The method used in vitro fertilization (IVF) with eggs from two women and sperm from one man to prevent fatal genetic diseases. Although this was legally permitted 10 years ago, this is the first time detailed analysis results have been released.
Researchers at Newcastle University and Newcastle University Hospital noted on the 16th (local time) that "they blocked fatal genetic diseases by transplanting mitochondria donated by healthy women into eggs." The research results were published that day in two papers in the international journal 'New England Journal of Medicine (NEJM)'.
Mitochondria are organelles that produce energy outside the cell nucleus. Most of the genetic material DNA is located in the cell nucleus, but about 0.1% is found in mitochondria. Mitochondrial DNA is only present in eggs and is inherited maternally. If a mutation occurs in mitochondrial DNA, it can affect energy-intensive tissues such as the heart, muscles, and brain, leading to serious diseases. Approximately 1 in 5,000 babies is born with a mitochondrial DNA mutation each year, but there is currently no known treatment.
By applying pronuclear transfer during fertilization, women with mitochondrial DNA mutations can also give birth to healthy babies. It is a method of transferring the nucleus of the egg, as the name suggests.
First, the nucleus is removed from the egg donated by a healthy woman. Next, the nucleus is taken from the fertilized egg with mitochondrial mutations and transferred into the donor's egg. This way, the normal nuclear DNA is received from the parents, and the mitochondrial DNA is received from the donor. This means that there are three parents who contributed genes.
This method is also known as mitochondrial donation. It was first legalized in the UK in 2015. Currently, it is officially authorized in the UK and Australia, while there have been some cases in countries like Mexico and Ukraine, but they are not classified as officially authorized countries. The U.S. and Canada have explicitly banned pronuclear transfer IVF. Korea has effectively banned it as well.
Researchers at Newcastle University have been developing and optimizing techniques to apply pronuclear transfer to embryos. In 2023, The Guardian reported that five babies were born through mitochondrial donation, but detailed information about their health status or the effectiveness of the procedure has not been disclosed. The researchers reported results from a study involving 22 women subjected to pronuclear transfer IVF and subsequent follow-up.
According to the researchers, all eight babies were born healthy. Some babies experienced temporary seizures, urinary tract infections, and hyperlipidemia, but they were treated sufficiently, and these issues were analyzed as not directly related to the mitochondrial donation procedure.
In particular, there were no signs of genetic diseases caused by mitochondrial mutations. Disease genes were hardly detected in blood and urine, or appeared at levels far lower than the 80% threshold for disease manifestation. The researchers explained that the detection of some disease genes was due to residual mitochondria surrounding the nucleus of the embryo.
Doug Turnbull, a professor at Newcastle University, said, "This technology could provide a way to prevent the transmission of diseases to babies for women at risk of passing on mitochondrial mutations." A woman who gave birth to a healthy baby through pronuclear transfer remarked, "Thanks to this technology, my child was able to start a healthy life," adding, "Science has given us this opportunity."
The researchers plan to regularly monitor the health status of the children until they reach the age of 5. Mary Herbert, a professor at Newcastle University, said, "Through research to understand the limitations of pronuclear transfer, we can further improve treatment outcomes."
References
New England Journal of Medicine (2025), DOI: https://doi.org/10.1056/NEJMoa2415539
New England Journal of Medicine (2025), DOI: https://doi.org/10.1056/NEJMoa2503658