The creation of babies using sperm and eggs from three people has moved a step closer in the UK.
A public review into the three person IVF technique has been broadly supportive, says the Department of Health.
But a number of technical and scientific details need to be finalised before the plans go before Parliament.
This may lead to muscle weakness, blindness, and heart failure.
Using the parents’ sperm and eggs plus an additional egg from a donor woman should prevent such conditions, say scientists at Newcastle University.
An expert scientific panel has already suggested there is no evidence the procedure is unsafe but has asked for a number of further investigations to be carried out.
The government expects other details to be finalised in the next few months before the plans are legalised.
A public consultation received nearly 2,000 responses.
Ministers agreed that the regulatory body the Human Fertilisation Embryology Authority would consider each application from parents on a case-by-case basis.
And any children born using the procedure would not be able to find out the identity of the mitochondrial donor.
Mitochondria are tiny, biological “power stations” that provide energy to nearly every cell of the body.
As mitochondria are passed down from mother to child, using an extra egg from a donor woman could give the child healthy mitochondria.
However, it would also result in babies having DNA from two parents and a tiny amount (1%) from the donor as mitochondria have their own DNA.
Opponents say it is unethical and could set the UK on a “slippery slope” to designer babies.
Dr Jeremy Farrar, director of the Wellcome Trust, said: “There is broad public support for making mitochondrial replacement therapy available to patients.
“There is now no excuse for the Government not to table regulations for debate as soon as Parliament returns this autumn, so that the HFEA can licence clinics to treat affected families without delay once it is satisfied that any risks are acceptable.”
Sarah Norcross, director of the Progress Educational Trust, said: ‘While we welcome the Government’s decisions, we are disappointed by the time it has taken to reach this point in the process.
“A year ago, the Government promised a consultation in autumn 2013 which ultimately took place in March 2014.
“We note that the Government now aims to provide an update by early autumn 2014 – we hope that this is not similarly delayed.”
Dr David King, director of Human Genetics Alert said: “Looking back 15 years from now in the midst of a designer baby marketplace, people will see this as the moment when the crucial ethical line was crossed.
“A precautionary approach would demand much more evidence and the government would wait for that rather than rushing legislation through.”