Eight babies have now been born in the UK with genetic material from two women and one man.

LondonTen years after the UK legalized the possibility of using genetic material from three people to obtain a healthy embryo and avoid life-threatening mitochondrial problems, scientists at Newcastle University conducting the first clinical trial of this technique have confirmed the birth of eight healthy babies using this method. Just over two years ago, the UK's Human Fertilization and Embryology Authority (HFEA) confirmed that until April 20, 2023 there were five, those born of two mothers and a father, within the framework of this trial.

The procedure, not without controversy at the time of approval due to the doors it opens to the possibility of creating babies on demand, is carried out to reduce the risk of suffering from so-called mitochondrial diseases, which have very serious consequences. The results of the study have been released this Wednesday in New England Journal of MedicineAccording to researchers, four girls and four boys—including a pair of identical twins—were born as a result of the procedure, which was applied to seven women at high risk of transmitting mutations in their mitochondria. The children, ranging in age from a few weeks old to more than two years old, are developing normally and show no signs of hereditary disease. Another woman of the 22 who underwent this clinical experiment is still pregnant.

Despite the involvement of a third person's DNA—which is why these children are popularly called babies of three parents– To obtain a healthy egg, almost all of a newborn's genes come from both parents. Only about 0.1% of the third person, a healthy donor, is used in the process.

heart failure or brain disorders. The consequences can be fatal within a few days or even a few hours after birth. Mitochondria impede the body's nutrition and cause a whole range of irreversible damage. How does the technique work?

Mitochondrial transfer involves transferring the nucleus of a fertilized egg from a woman carrying harmful mutations into a given egg from which the nucleus has been removed. This allows the resulting embryo to have nuclear DNA from both biological parents and healthy mitochondrial DNA from the donor. This method is, in many cases, the only option for potential carriers of the disease, because conventional in vitro fertilization does not always generate embryos healthy enough to implant after preimplantation diagnosis.

In 2017, Newcastle University was granted permission to conduct this clinical trial, funded by the National Health Service (NHS) and the Wellcome Trust. The trial was originally intended to treat 125 women over five years, but the process has been slower due to a lack of donors and the technical challenges associated with in vitro fertilization. Specialists offered two options to women with pathogenic mitochondrial DNA variants: pronuclear transfer, through which all eight babies have already been born, or preimplantation genetic diagnosis (PGT).

PGT involves screening embryos created by in vitro fertilization (IVF) before transferring them to the uterus to ensure they do not present genetic abnormalities. In this case, embryos with lower levels of affected mitochondrial DNA are chosen to reduce the risk of disease. Patients with heteroplasia (variants present in only some of the mitochondrial DNA copies) underwent PGT, while those with homoplasia (variants in all copies) or high levels of heteroplasia opted for pronuclear transfer.

In total, clinical pregnancies were confirmed in 36% of women who chose pronuclear transfer (the aforementioned 8 out of 22, of which seven women have already given birth) and in 41% of those who opted for PGT (16 out of 39), who have completed their term. Currently, only the United Kingdom and Australia legally permit mitochondrial transfer.

In the mid-2000s, the United Kingdom became very aware of these problems of genetic transmission following the case of Sharon Bernardi, a woman who lost seven children due to diseases derived from mitochondrial malfunction. The law that made this scientific advance possible was passed by a majority of 254 votes.