Scientists have created and fertilised an egg with two biological mothers and one biological father, sparking ethical fears about babies grown from three-parent embryos.
The Japanese researchers used material from the eggs of young donors to repair damaged eggs from older mothers.
The two-mother eggs were injected with sperm from a man to create an early stage embryo.
One of the scientists behind the study said he believed the “success rate would be high” if the embryos could be transferred into a womb.
IVF treatment often does not work for older women because of abnormalities in the outer part of their eggs, known as cytoplasm, which surrounds the central nucleus.
The team at St Mother Hospital in Kitakyushu, Japan, sought one way around the problem by transferring the healthy nucleus into cytoplasm from a donor.
The team created 31 two-mother eggs and of these seven were fertilised to form “early stage embryos”. The embryos contained DNA from three genetic parents.
Last year at Newcastle University scientists also created embryos from three genetic parents using a different process.
The Newcastle scientists claim they were able to transplant the nucleus from one pre-fertilised egg to an egg from another woman that had already had its nucleus removed.
They created ten such embryos, containing DNA from both original parents as well as the egg-donating mother. The embryos were allowed to develop for 6 days before being destroyed.
There have been concerns about these techniques introducing new and unforeseen genetic problems.
Fears about the potential psychological damage to a child born to three genetic parents have also been raised.
Referring to the embryos used in researching this procedure, pro-life campaigner Josephine Quintavalle said: “It is human beings that they are experimenting on.”