Britain is set become the world’s first nation to legally approve “three-person” babies after an historic vote in the House of Commons. Today’s move means that DNA from two women and a man can now be pooled in order to outweigh the odds of an embryo developing mitochondrial disease— where cells unable to generate energy begin closing down altogether—ultimately causing issues including brain damage, muscle wasting, and death.

Fifteen years after it was first proposed, the 1990 Human Fertilization and Embryology Act is on the cusp of amendment. Members of British parliament (MPs) voted 382-128 in favor of updating the regulation, which could take effect on October 29 if approved by the House of Lords next month.

There are currently two techniques being devised, but the procedure—if and when it gets passed—will share the same key aspect: taking the DNA from the parents and combining it with the healthy mitochondria of a female donor. As the structures are solely passed down to offspring through the maternal line, any faulty material would be replaced by another female donor, replacing 0.1 percent of the embryo’s genes. Though scientists say full validation of the process can only come after it has been trialled on a human, signs are positive that it will be successful in providing a major step forward in reducing the number affected by the disease.

Every day, up to 4,000 children in the US and 6,500 in the UK are born with mitochondrial disease, making this ruling an important step in reducing its prevalence worldwide. While there are currently no laws prohibiting the procedure here, this is the closest it has come to getting officially sanctioned, enabling a medical revolution akin to that of the world’s first test tube baby in 1978.

Legally allowing the genetic modification of embryos has long rendered mitochondrial donation a controversial topic, with dissenters—namely the Church—questioning its safety.

“No other country has allowed this procedure and the international scientific community is not convinced that the procedure is safe and effective,” said Roman Catholic bishop the Right Reverend John Sherrington. “There are also serious ethical objections to this procedure which involves the destruction of human embryos as part of the process.”

“What’s the rush?,” added Reverend Brendan McCarthy, the Church of England’s adviser on medical ethics.

But for mothers like Sharon Bernardi, who lost all seven of her children as a result of mitochondrial disease, these changes to the law cannot come soon enough. “No child should be born with a disease that’s going to cut their life short. I can’t believe anybody from the Church would want that,” she told the BBC.

While critics have also denounced three parent embryos for enabling “designer babies”—where parents are allowed to select its genetic makeup—Bernardi explains that this amendment is not a legal loophole for superficially choosing a child’s physical features, such as eye or hair color. “We’re not playing God,” she said. “This is trying to make children survive.”

This issue of whether this process would constitute as genetic modification was perhaps the most challenging aspect of the debate, with one minister suggesting that society would be “up in arms” should we allow the same process to occur within crop growth. But the claim was dismissed by Public Health Minister Jane Ellison, who likened it to the changing of a battery pack of a cell, emphasizing that this would not lead to parents switching out their unborn babies’ less desirable traits. “These regulations can only be applied to severe mitochondrial diseases. This is not a slippery slope,” she stressed.

“This is a bold step for Parliament to take, but it is a considered and informed step,” she said during the debate. “For the many families affected, this is light at the end of a very dark tunnel.”