A medical team in the United Kingdom has successfully used a new reproductive technique to help eight babies be born without mitochondrial diseases. The study was published on July 16, 2025, in the New England Journal of Medicine. Mitochondrial diseases are rare but serious genetic conditions. They are caused by damaged mitochondria, which are parts of cells that produce energy. These diseases can lead to muscle weakness, seizures, organ failure, and sometimes fatality. The method, called mitochondrial replacement therapy, aims to prevent mothers from passing these diseases to their children. Scientists first performed the procedure in the United Kingdom in 2016, after it received official approval. Australia has also legalized this method, but it remains banned in many countries, including the United States.

In the study, researchers used the technique on fertilized embryos from 22 patients. As a result, eight healthy babies were born without signs of mitochondrial disease. One more pregnancy is still in progress. Mitochondrial replacement therapy involves moving the mother’s DNA into a healthy donor egg with working mitochondria. The donor’s original genetic material is removed. The embryo then contains DNA from three people: the mother, the father, and a donor. Scientists say the donor DNA is less than 1% of the baby’s total DNA, so the baby will not inherit the donor’s appearance. Some experts warn about possible long-term effects.