In a move described as "bold" by supporters and potentially reckless by detractors, Britain's House of Commons voted overwhelmingly Tuesday to allow the creation of babies using DNA from three people.
Lawmakers spent 90 minutes debating the bill, an attempt to prevent potentially fatal diseases being passed on to children. The legislation, passed by a 382-128 vote, needs the approval of the House of Lords but is unlikely to meet major opposition.
If it becomes law, it will open the door this year for scientists to create an embryo with DNA from two women and one man. The first such child created in Britain could be born in 2016.
"This is a bold step for Parliament to take, but it is a considered and informed step," Public Health Minister Jane Ellison said. "And for the many families affected, this is light at the end of a very dark tunnel."
However, critics said the legislation could pave the way to so-called "designer babies."
"We believe the House of Commons has made a serious mistake, which we hope does not have dire consequences," said Marcy Darnovsky, executive director of the California-based Center for Genetics and Society. "We sincerely hope that scientists, policymakers and others will join us in working to strengthen the widespread commitment to forgo efforts to modify the traits of future children and future generations."
Researchers have spent years perfecting a technique developed at the University of Newcastle, in the north of England, to prevent diseases caused by mutations in mitochondrial DNA, a short string of genetic material passed directly from mother to child that controls the energy sources of cells.
As many as one in 5,000 people are thought to be affected by mitochondrial diseases, which can cause muscle weakness, seizures, dementia, blindness, abnormal heart rhythms and other serious problems. Some mitochondrial diseases can be fatal.
The process would start with an egg from a healthy donor. Her mitochondrial DNA would be preserved, but her nuclear DNA — the genetic information stored in 23 pairs of chromosomes — would be removed and replaced with the nuclear DNA from the would-be mother. That hybrid egg would then be joined with sperm and implanted into the mother's womb, as in a typical in vitro fertilization procedure.
Far less than 1% of a newborn's DNA would come from the woman who donated the egg. Her mitochondrial DNA would have no effect on characteristics such as appearance, since these are based on nuclear DNA, which is inherited from both mother and father.
In the United States, a different in vitro fertilization technique was used to conceive a child with DNA from three people in 2000. That process was later banned over safety and ethical concerns.
Members of the scientific community were quick to express their joy Tuesday over the approval of the British bill.
"We have finally reached a milestone in giving women an invaluable choice, the choice to become a mother without fear of passing on a lifetime under the shadow of mitochondrial disease to their child," said Robert Meadowcroft, chief executive of the London-based Muscular Dystrophy Campaign.
Lawmakers were told they were free to vote on the measure as an issue of conscience, and not along party lines.
British Prime Minister David Cameron voted in favor of the legislation, saying it was not "playing God" but offered parents the chance to have a healthy baby.
The Roman Catholic Church disagreed.
"The human embryo is a new human life with potential; it should be respected and protected from the moment of conception and not used as disposable material," Bishop John Sherrington said in a statement issued on behalf of the church in England and Wales.
The Church of England said it was not in favor of "preventing people from benefiting from a major advance in genetics and assisted reproduction." Rather, it said in a statement, "we want to ensure that as a nation we get such a significant treatment and its regulation right."