Scientists at Newcastle University have reported the birth of eight healthy children after using a three-person in-vitro fertilisation procedure that swaps faulty maternal mitochondria for healthy donor mitochondria. The results, detailed in two papers in the New England Journal of Medicine, mark the first peer-reviewed evidence that mitochondrial donation therapy can prevent the transmission of otherwise incurable inherited disorders. The method, known as pronuclear transfer, involves fertilising eggs from both the affected mother and an anonymous donor with the father’s sperm, then transferring the parents’ combined nuclear DNA into the donor embryo, which contains healthy mitochondria. Of 22 women treated, seven became pregnant and delivered four boys and four girls, including one set of identical twins; a ninth pregnancy is ongoing. Follow-up tests show that six of the newborns carry no—or only trace—levels of the disease-causing mitochondrial mutations found in their mothers, while the remaining two exhibit reductions of 77-88 per cent. One child developed high blood lipid levels and an arrhythmia that resolved with treatment, and another experienced transient epilepsy, but researchers say no complications have been linked to the mitochondrial procedure. The oldest of the children is now two years old and all have met developmental milestones. The United Kingdom was the first country to legalise mitochondrial donation in 2015, and the Human Fertilisation and Embryology Authority licences each case individually. The therapy remains prohibited in the United States. Researchers plan long-term monitoring of the children, but the early data bolster hopes that the technique could offer families at high genetic risk a viable route to having healthy, genetically related offspring.