A child, three parents. It might seem science fiction , but it is already a reality . It is a reality that began a decade ago, with the approval in the United Kingdom of a novel technique that allowed the introduction of genetic information from a third person during an in vitro fertilization process.
Eight births. The British team that launched this technique has published the results obtained from monitoring nine babies born after an in vitro fertilization process. This process has an important peculiarity: the introduction of mitochondrial DNA from a donor.
Mitochondrial diseases. To understand the scope of this new procedure, we first need to grasp the reason that led to its development: to avoid the transmission of mitochondrial DNA diseases. It is estimated that this problem affects around 5,000 births per year .
The mitochondria are the energy producers within cells, and they also contain a segment of DNA that is inherited matrilineally. This means that only mothers can pass it on, even though the resulting diseases can affect individuals of any sex.
This mitochondrial DNA can contain harmful mutations that disrupt the normal function of this energy powerhouse , leading to diseases that predominantly affect energy-demanding tissues, such as those in the heart and brain. While we do not currently have a cure for these diseases, we now have a method to prevent their transmission.
Pronuclear transfer. This innovative technique, known as pronuclear transfer, is performed after the fertilization of the egg. It involves transplanting the nuclear genome of the mutated egg into a new donor egg, resulting in a cell that contains the parents’ nuclear DNA accompanied by the mitochondrial DNA from the donor.
Studying the technique. The intricate details of this study were detailed in two articles published in the journal New England Journal of Medicine. The first article focused on the technique’s success rate.
The technique did not completely eliminate the original mitochondrial DNA. During the core extraction process, some of this DNA also got introduced into the new cell. The researchers stated that mitochondrial DNA in the blood of the neonates ranged from undetectable levels up to 16% .
“The findings inspire optimism. However, continued research to better understand the limitations of mitochondrial donation technologies will be essential to improving treatment outcomes,” explained Mary Herbert, the lead researcher of this study.
Healthy babies. A second study concentrated on clinical results, assessing the health of both mothers and infants. Throughout the pregnancies, only one complication was observed in a mother—hyperlipidemia, which is an excess of blood lipids . Fortunately, this was manageable with prescribed treatment.
The eight babies were born healthy, and their development has been normal during the study. Most infants showed no health problems, while the few mild issues detected were not attributed to the donation process.
As for the success of the procedure, the team found no mitochondrial DNA in five of the eight babies. Among the three babies with detectable mutations, the levels remained below 20% , a stark contrast to the 80% threshold at which complications could arise. Ongoing monitoring of these cases remains critical for a complete understanding of long-term effects.
Ethical considerations. This monitoring will be vital for alleviating concerns regarding the potential long-term impacts of this new technique, an essential factor in the ethical discussions surrounding the practice. While the United Kingdom approved this method in 2015, many nations still have not legislated in this area.
“The study also prompts ethical and scientific inquiries. Merging nuclear and mitochondrial DNA from different individuals could yield long-term effects that remain largely unknown,” noted Rocío Núñez Calonge, the scientific director of the International UR Group and coordinator of the Ethics Group at the Spanish Fertility Society.
And in Spain? As of now, Spain remains in a legal limbo, lacking clear legislation on this subject. Experts explain that the existing laws on assisted reproductive technologies do not explicitly address this process, meaning it is neither explicitly prohibited nor authorized.
“In Spain, our current legislation on assisted human reproduction techniques does not mention this technique, which did not exist when the law was enacted. Therefore, in a sensu stricto sense, the procedure is simply unregulated,” Lluís Montoliu explains, a researcher at the National Biotechnology Center (CNB-CSIC).
While the practice of allowing three parents to conceive a child raises significant medical, ethical, and legal considerations, the advances made in mitochondrial donation could offer hope to many families affected by genetic disorders. Continuous monitoring and research are essential to navigate the complexities of this groundbreaking development.