The Nuffield Council on Bioethics said the treatments - which have become known as three-parent in vitro fertilization (IVF) because the offspring have genes from a mother, father and from a female donor - should be offered to affected families together with full information and expert support.

"If these treatments are successful, these children would be among the first in the world to have a genetic connection to not two people, but three people," said Geoff Watts, who chaired a Nuffield inquiry into the issue. "There are a number of ethical questions that arise and needed to be considered."

Around one in 6,500 children worldwide are born with serious diseases caused by faulty mitochondrial DNA.

Britain is widely considered to be at the forefront of research in this area, so ethical considerations and scientific advances here are likely to be closely watched around the world.

The new potential treatments involve intervening in the fertilization process to remove faulty mitochondrial DNA, which can lead to a range of inherited conditions including fatal heart problems, liver failure, brain disorders, blindness and muscular weakness.

Still at the research stage, the treatments effectively replace mitochondria, which act as tiny energy-generating batteries inside cells, so a baby does not inherit faults from its mother. Mitochondria are only passed down the maternal line.

"If further research shows these techniques to be sufficiently safe and effective, we think it would be ethical for families to use them ... provided they receive an appropriate level of information and support," said Watts.

Speaking at a briefing about the inquiry's conclusions, he said the new treatments could offer significant health and social benefits to affected families, allowing them to live "free from what can be very severe and debilitating disorders", and to have children without needing to adopt.

"This is a way in which parents can have children who are genetically related to them," Watts said. "And the descendants of any woman born via these therapies should inherit healthy mitochondria and be free of mitochondrial disorders."

GERMLINE THERAPY?

There are various potential techniques. One being developed by scientists at Britain's Newcastle University, known as pronuclear transfer, swaps DNA between two fertilized human eggs. Another, known as the maternal spindle transfer, swaps material between the mother's egg and a donor egg before fertilization.

Medical experts welcomed the ethics report, saying it had rightly raised and clarified important issues in good time before potential treatments become available.

"Scientific progress that benefits human health is at its most effective when such questions can be raised and treatments are developed in a transparent and consultative manner," said Catherine Elliott of the Medical Research Council (MRC).

Watts said the inquiry had also considered whether the proposed treatments would be a form of so-called "germline therapy" - since the changes resulting from replacing mitochondrial DNA would be passed on not only to the children, but also to future descendants of any girls born.

Although mitochondrial DNA swapping is not the same as altering the DNA inside a cell's nucleus, the Nuffield inquiry concluded it was nevertheless a form of germline therapy. But Watts stressed this did not mean the ethics body would approve any other forms of germline therapy, which are currently banned in Britain.

"Some people concerned about the idea of germline therapies may fear that if such treatments for mitochondrial gene disorders were approved, a slippery slope would be created towards comparable alterations to the nuclear genome," he said.

"(But) we are only talking about the use of these techniques in the clearly-defined situation of otherwise incurable mitochondrial disorders, under strict regulation."

(Editing by Andrew Roche)

• A Permanent Economic Emergency