Genetic experts have say it could take decades to confirm the safety of an experimental fertilisation technique that would create babies from the DNA of three people, with the aim of preventing children from inheriting some debilitating diseases.
The US Food and Drug Administration has heard from supporters and opponents of the provocative technique at a two-day meeting, as the agency considers whether to greenlight testing in women who have defective genes linked to blindness, organ failure and other inheritable diseases.
Preliminary testing in animals suggests that combining the DNA of two parents with that of a third female donor could allow prospective mothers to give birth to healthy children. But even experts in the field warned that researchers would have to follow the offspring for many years to see if they are truly healthy.
"The end of the experiment will come decades later," said Michigan State University's Keith Latham, in a presentation before the FDA and its advisory panel.
"It's going to take us that long to figure out the health of the progeny produced from these procedures."
The FDA explicitly framed its public meeting as a "technical" discussion on the feasibility of safely testing the artificial fertilisation technique in humans. In a statement read at the outset, FDA staffers acknowledged the "ethical and social policy issues related to genetic modification of eggs and embryos", but said such issues were "outside the scope of this meeting".
Despite such disclaimers, more than a half-dozen public speakers urged the FDA to block any human testing of the DNA-swapping technique due to unknown medical, ethical and societal impacts. Several argued that it could be a slippery slope toward "designer babies" - allowing parents to customise traits like eye colour, height and intelligence.
Marcy Darnovsky of the Centre for Genetics and Society said that FDA-sanctioned testing would cross a "bright policy line" into altering genes that will be passed down to future generations.
"It could well be the first time any jurisdiction in the world had authorised intentional genetic modification of children and their descendants. And it would be making this decision with little or no input from the public or elected officials," said Darnovsky. Her group points out that 40 countries - including Germany and France - have laws banning human genetic changes that are passed on to future offspring.
