THE possibility that babies could be born with the DNA of three different people is a step closer, after a consultation showed that most Britons would be happy to see the law changed to allow a radical form of gene therapy.
The IVF therapy would help women in danger of passing on mitochondrial disease to their babies - a potentially fatal metabolic disorder.
An exhaustive survey of public attitudes to the replacement of an affected mother's mitochondria - the tiny "power packs" of cells - with those from an egg donor has found widespread support for the technique.
"We've found that there is broad support for permitting mitochondria replacement to give families at risk of mitochondrial disease the chance of having a healthy child," said Professor Lisa Jardine, the chair of the Human Fertilisation and Embryology Authority (HFEA).
"Although some people have concerns about the safety of these techniques, we found that they trust the experts and the regulator to know when it is appropriate to make them available."
But David King, director of Human Genetics Alert, criticised the HFEA for ignoring the potential risks associated with the technique, which has had only limited testing on laboratory animals and is not medically practised anywhere in the world.
"These techniques go far beyond anything existing in both invasiveness to the embryo and complexity, so it's not surprising they pose serious health risks to the child - risks that the HFEA refuses properly to address," Dr King said.
Mitochondrial replacement involves fusing the egg-cell nucleus of the affected mother with an egg cell from an unaffected donor.
The donor egg has its own nucleus and its complement of chromosomes removed, but retains the donor's healthy mitochondria - which have their own DNA to control energy use within the cell.
Some form of mitochondrial disease affects around one in 200 children born each year, but severe symptoms occur in only about a few dozen new-born infants.
The disease results from defects in the mitochondrial DNA, but scientists believe these could be prevented by the technique of mitochondrial replacement from a donated egg cell.
After the egg cell of mother and donor is fused and fertilised by IVF it is implanted into the mother's womb in the usual way.
The resulting baby should be free of the mother's mitochondrial defects and subsequent generations should also be free of mutations in the mitochondrial DNA - a form of "germ-line" gene therapy.
The law covering IVF, the Human Fertilisation and Embryology Act, does not allow germ-line gene therapy, when the sperm or eggs are genetically altered, or the genetic modification of IVF embryos.
However, in 2008 the Act was amended to allow the Secretary of State for Health to permit techniques that prevent the transmission of mitochondrial disease.
In 2012, the Government asked the HFEA to seek views on mitochondrial replacement before it was made legal.
As a result, the authority commissioned a series of public consultations.