On Wednesday, Britain's fertility regulator confirmed that the first babies in the UK have been born using a new experimental technique that combines DNA from three people. This technique was developed to prevent rare genetic diseases from being inherited by the children. The Human Fertilization and Embryology Authority reported that fewer than five babies have been born this way in the UK, but no further details were provided to protect the families' privacy. The Guardian newspaper first reported this news.

In 2015, the UK became the first country in the world to adopt legislation specifically regulating methods to prevent women with faulty mitochondria, which is the energy source in a cell, from passing defects on to their babies. Mitochondrial defects can lead to diseases such as muscular dystrophy, epilepsy, heart problems, and intellectual disabilities. Approximately one in 200 children in Britain is born with a mitochondrial disorder. To date, 32 patients have been authorized to receive such treatment.

For women with faulty mitochondria, scientists take genetic material from their eggs or embryos. This material is then transferred into a donor egg or embryo that still has healthy mitochondria but has had the rest of its key DNA removed.

After fertilization, the embryo is implanted into the mother's womb. The donated egg's genetic material makes up less than 1% of the child created using this technique. The UK fertility regulator stated that "mitochondrial donation treatment offers families with severe inherited mitochondrial illness the possibility of a healthy child." However, the regulator requires every woman undergoing the treatment to receive approval and families must have no other available options for avoiding passing on genetic disease.

Critics argue that there are other ways to avoid passing on diseases such as egg donation or screening tests and that the experimental methods have not yet been proven safe. Some warn that this could lead to designer babies for parents who want not only to avoid inherited diseases but also to have taller, stronger, smarter, or better-looking children.

Robin Lovell-Badge, a stem cell expert at the Francis Crick Institute, emphasized the importance of monitoring the babies' future development. Researchers are interested in knowing whether the mitochondrial donation technique worked practically, whether the babies are free of mitochondrial disease, and whether there is any risk of them developing problems later in life.

Scientists in Europe have shown that in some cases, abnormal mitochondria carried over from the mother's egg to the donor's can reproduce when the baby is in the uterus, which could lead to a genetic disease. Lovell-Badge stated that researchers would need to develop methods to reduce this risk. Doctors in the US announced the birth of the world's first baby using the mitochondria donation technique in 2016 after conducting the treatment in Mexico.