Scientists in Britain are claiming a medical first, creating human embryos with the genetic material of three people: one man and two women.
Researchers from Newcastle University, in northern England, presented their findings at the Medical Research Council Centre for Neuromuscular Diseases conference in London this past weekend.
The embryos were created using in vitro fertilization. The doctors took the eggs on one woman, then removed the egg's mitochondria, which are contained outside the nucleus in a normal female egg. The mitochondria were then placed into the eggs of the other woman whose mitochondria had been removed.
The 10 embryos were destroyed after six days. But had they been allowed to grow, the resulting fetus would have inherited the nuclear DNA, or genes, from the man and one of the women, as well as the mitochondrial DNA from the second woman.
The scientists say their research could become an effective treatment for a range of serious hereditary diseases. The "mitochondrial transplant" that the researchers were able to achieve could help women with faults in their mitochondrial DNA from passing diseases on to their children.
Around one in 5,000 children suffer from mitochondrial diseases, which can include muscular dystrophy, epilepsy, strokes and mental retardation. Mitochondrial DNA is passed down only through the female line.
Mitochondria provide a cell with its energy. Faulty genetics can mean mitochondria do not completely burn their food, creating a build-up of poisons that can lead to more than 40 diseases.
The technique has so far been tried only in the laboratory, using abnormal embryos left over from IVF therapy. But similar experiments have been conducted in animals in Japan. The resulting baby mice were healthy, those researchers say.
Much more testing will be necessary to assess the safety and efficacy of the process. But if all goes well, researchers believe they may be able to start offering the technique to humans as a treatment for mitochondrial diseases in three to five years.
Patrick Chinnery, a professor of neurogenetics at Newcastle University involved in the research, says only trace amounts of a person's genes come from the mitochondria and most of our genes are inside the nucleus. So, technically, it is incorrect to say that the embryos have three parents.
The research was funded by the Muscular Dystrophy Campaign, a British charity.
