The UK has become the first country in the world to legalise the creation of IVF babies using DNA from three people.
The first baby conceived after mitochondrial donation techniques may be born as early as next year after peers in the House of Lords voted against a move to block a planned law change by 280 votes to 48, a majority of 232.
Research has shown that mitochondrial donation could potentially help almost 2,500 women of reproductive age in the UK who are at risk of transmitting harmful DNA mutations in the mitochondria.
But opponents, including church leaders and pro-life groups, have warned that the change has been brought about too hastily and marked the start of a “slippery slope” towards “designer babies” and eugenics.
On Tuesday night peers rejected an attempt to delay the legislation by Tory former cabinet minister John Gummer, now Lord Deben, before voting overwhelmingly in favour of the change to the law after several hours of debate.
The move to amend the 2008 Human Fertilisation and Embryology Act, which forbids IVF treatments that affect inherited “germline” DNA in eggs and sperm, was carried by 382 votes to 128 in the Commons earlier this month.
Prime minister David Cameron, Labour leader Ed Miliband and deputy prime minister Nick Clegg exercised their free vote to support the decision.
A department of health spokeswoman said: “Parliament’s decision will bring hope to hundreds of families affected by mitochondrial disease. We are proud to be the first country to allow these revolutionary techniques. For the first time ever, women who carry severe mitochondrial disease will have the opportunity to have healthy babies without the fear of passing on devastating genetic disorders.”
Children conceived after mitochondrial donation would have “nuclear” DNA determining individual traits such as facial features and personality from its two parents, plus a tiny amount of mitochondrial DNA (mDNA) from an anonymous woman donor.
Critics have pointed out no clinical trial has taken place to show conclusively that the treatments are safe in humans.
However, three separate expert reviews for the Human Fertilisation and Embryology Authority (HFEA) found that the procedures are ready to go forward.
Alastair Kent, director of the Genetic Alliance UK charity, which helps people with inherited conditions, called the vote a "triumph", while health minister Earl Howe said it would be "cruel and perverse" to deny for any longer than was necessary the chance of some women who carry serious inherited diseases to have healthy children.
He said the move to permit the controversial procedures, aimed at preventing serious inherited, mitochondrial diseases, offered “real hope” to families.
Lord Deben’s unsuccessful motion rejected the law change until a joint committee of MPs and peers had reported on safety procedures.
He had argued it had not yet been proved the techniques were safe and there was uncertainty about their legality.
He told peers: “We are trying to protect three sets of people — families, mothers and fathers; children; and the wider society.
“We would be the first country in the world to allow this. We have to be very careful that we do so with full and whole-hearted support and also that we have fulfilled the safety needs.”
The Bishop of Carlisle, the Rt Rev James Newcome, said the Church of England was not opposed in principle t "basically very much in favour" of the development, but " at the same time we have always counselled a degree of caution given the potential implications of this development."