Researchers have found a potential way to correct an inherited disorder affecting thousands of women.
Working on monkeys, they transferred genetic material needed to create a baby from a defective egg to a healthy one, resulting in healthy births.
The US work, featured in the journal Nature, raises hopes of a treatment enabling women with defective eggs to have a child without using donor eggs.
However, the child would have a small number of genes from a "third parent".
The treatment would involve so-called "germ line" genetic changes which would be passed down through generations.
The genetic fault is contained in structures in the egg called the mitochondria, which are involved in maintaining the egg's internal processes.
If an egg with faulty mitochondria is fertilised the resulting child could have any of hundreds of different diseases including anaemia, dementia, hypertension and a range of neurological disorders.
US researchers have previously tried and failed to correct this defect by adding healthy donated mitochondria into the eggs of patients wishing to have children.
But these attempts resulted in birth defects - probably because mitochondria are so delicate that they are damaged when they are transplanted from one egg to another.
As a result, the treatment was banned by the US until it could be demonstrated that it was safe in animal experiments.
A group at the Oregon Health and Science University has now done just that.
They transferred the DNA needed to make a baby out of monkey eggs, leaving behind the potentially diseased genes in the mitochondria.
This was transplanted it into eggs emptied of DNA but containing healthy mitochondria.
The technique resulted in three healthy births with no sign of any birth defects.
Lead researcher Dr Shoukhrat Mitalipov believes the technology is now ready to be tried out on human patients.
He said: "It is estimated that every 30 minutes a child is born with this devastating disease and I believe we could prevent that."
Dr Mitalipov has applied for a research licence to work with human eggs and embryos, and hopes to work with patients soon.
He said: "Moving to human trials could be very quick, maybe within two to three years.
"This type of gene therapy is much closer to clinical application than anything else before."
The development has been welcomed by Professor Peter Braude, an IVF specialist at Guys and St Thomas's hospital.
He said: "It is a very nice approach that could potentially help thousands of women with mitochondrial disease."
But some groups have expressed concern that this method involves making a genetic change to an egg that can be passed down through generations.
Dr Helen Wallace, of the campaign group GeneWatch, said: "The fact that treatment effects would persist for generations means ethical debate is needed, as well as more safety tests."
But according to Professor Robin Lovell-Badge, of the National Institute for Medical Research in Mill Hill London, people should not worry unduly over the germ-line alterations.
He said: "Mitochondria do not confer any human-specific qualities.
"It would be similar to changing the bacteria in our intestines, which I suspect no one would care about.
"Altering the nuclear genome is a different matter. As it would be difficult and risky there would have to be very good reasons for doing this."
In the UK, the Human Fertilisation and Embryology Authority has licensed a number of tightly-controlled research projects into mitochondrial diseases.
But Parliament would have to change the law to allow the technique to be used on patients.