Britain's fertility regulator has decided that "three-parent baby" treatments can go ahead, opening the way for parents to be treated as early as next spring. This landmark decision makes Britain the first country in the world to offer licenses for this treatment. Earlier this year, a baby was born in Mexico through the technique.

The board of the Human Fertilization and Embryology Authority (HFEA) had been tasked with deciding whether clinics should be allowed to apply for permission to carry out mitochondrial replacement therapy (MRT). "It is a decision of historic importance," said Sally Cheshire, chair of the HFEA.

The treatment aims to replace abnormal genes in the mitochondria, tiny, battery-like elements of cells that generate energy. Mitochondria hold just 0.1 percent of a person's DNA. It is always inherited from the mother and has no influence on characteristics like appearance or personality. Faulty mitochondria can cause a wide range of potentially fatal conditions affecting the body's vital organs, muscles, vision, growth, and mental capacity.

The treatment, pioneered by scientists at the University of Newcastle, transfers the genetic material that effectively encodes a baby's identity into a donor egg, whose own nuclear DNA has been removed. The end result is an embryo containing healthy mitochondria from the donor, and nuclear DNA from the baby's mother and father. Theoretically, this treatment can prevent a child from developing inherited diseases, and protect future generations.

Landmark decision

Around one in 10,000 newborns are affected by mitochondrial disease. The effects are devastating. Many children born with these conditions die very young, as the harmful mutations cause the brain, heart, or muscles to fail: effectively, the cells do not have the energy to keep these vital organs going.

Designer babies or an end to intractable illnesses: A revolutionary technology is allowing scientists to rewrite the genetic code.

"Mitochondria are such an integral part of every cell in our body that when there is dysfunction, they have the capacity to impact all organs and all systems of our bodies, so they're often very debilitating multisystem disorders," explains Lydia Leon, researcher into pregnancy at University College London's Institute of Child Health. "This technology brings the chance of a healthy birth to families who otherwise would be affected."

For people affected by disease such as muscular dystrophy, the decision is a huge step. "It's a landmark decision for couples affected by mitochondrial disease," said Beth Thompson, senior policy advisor at the Wellcome Trust, a charitable foundation that financially supported the research. "At the moment there are couples who have no option to have a baby that is both healthy and genetically related to them. This decision by the HFEA is absolutely fantastic news for those families who are the people ultimately best placed to decide whether this is the right thing for them."

An independent panel of experts had previously recommended "cautious adoption" of MRT. The HFEA will still have to approve every clinic and every patient before the treatment can go ahead. "We're the first country to legalize this within a regulatory framework and a review process which included independent ethics reviews and scientific reviews," adds Thompson. "We can now go ahead in a country where there's a robust regulation and with the capacity to follow up. As these babies are born as a result of this new technique, we'll be able to follow them and refine the technique and make sure it's used as safely and effectively as possible"

Playing God?

As with any development on the emotive topic of human genetics, the research has not been without controversy, with critics raising ethical concerns. The "Daily Express" newspaper responded to the news with the headline: "Should we be meddling with genetics and playing God?"

Critics have argued that the technique is not foolproof and that small numbers of faulty mitochondria might still be "carried over" into the child, and could replicate in the developing embryo. They have also argued that replacing the mitochondria might have more impact on personal traits than envisaged. Another criticism is that unknown epigenetic effects – environmental influences that alter the way genes work – could have serious consequences for the health of babies. "It is vital that scientists' enthusiasm does not override the welfare of the child," said Dr David King, director of the pressure group Human Genetics Alert.

"There is a lot of negative discussion around reproductive health technologies, but developments that will increase healthy life and reduce suffering are to be celebrated," says Leon. "It's great that this has come through in such a thoughtful way: it is a triumph of regulatory healthcare. It's a very progressive move."

Scientists at the University of Newcastle say that they have women already lined up for the therapy, and hope to treat up to 25 women per year with National Health Service (NHS) funding. They have issued an appeal for women to come forward to donate their eggs.