An exclusive report by Jessica Hamzelou in New Scientist confirms that the first child with DNA from three parents was born five months ago after American doctors performed a mitochondrial donation in Mexico. Though the idea is controversial and sounds like the makings of a sci-fi movie, the researchers had good reason for attempting the technique. Using DNA from a donor egg allowed them to bypass a fatal genetic disease carried by the child’s mother.

In 2005, the unnamed Jordanian couple gave birth to their first baby after four heartbreaking miscarriages. But there was a problem. Their infant daughter had Leigh syndrome, an inherited disease passed on through the mitochondrial DNA, the cellular "powerhouse" directly passed down from mother to child. The disease causes weakness, paralysis, nerve degeneration and eventually death. Their first child passed away at the age of six. A second child, reports Hamzelou, passed away at the age of eight months.

Desperate for a healthy baby, the couple contacted American physician John Zhang at the New Hope Fertility Center in New York, who has been investigating a way around mitochondrial diseases through a method he calls the “three parent technique” or mitochondrial donation.

There are two ways to perform the technique. In the first, known as pronuclear transfer, the mother’s egg and a donor egg are fertilized by the father’s sperm. After that, the nuclei of both fertilized eggs are removed and the donor nucleus is discarded. The mother’s nucleus is inserted into the donor egg. The resulting embryo then has the mother's nuclear DNA and the donor’s mitochondrial DNA.

The second technique, which Zhang and his team opted to use because of their patient's religious objection to discarding embryos, is called spindle nuclear transfer. In this technique, the team replaced the nuclei of the donor's egg with that of the mother and then fertilized the egg. They performed the technique on five eggs, but only one developed normally. The team implanted the resulting embryo in the mother who carried it to term.

Now five months old, the boy appears healthy. His mitochondria only carry about one percent of the mutations that cause Leigh’s, much lower than the 18 percent that is considered the threshold for producing symptoms.

This technique is not currently legal in the U.S., so Zhang and his colleagues performed the procedure in Mexico, where no regulations are in place against three parent children. In February, a panel from the U.S. National Academies of Sciences, Engineering, and Medicine released a report declaring that testing the technique is ethical. But the FDA has not yet approved U.S. testing of mitochondrial donation.

In February 2015, the UK Parliament passed legislation allowing the technique, which James Rush at The Independent reports could help more than 2,400 women in that country, though it has yet to be performed in that country.

A similar technique, cytoplasmic transfer, was attempted in the 1990s. But after about 100 procedures, the FDA banned it due to concerns about genetic abnormalities from injecting the cytoplasm of a donor egg into a host egg.

Though Zhang and his team skirted U.S. law by performing the technique in Mexico, Sian Harding, a professor of cardiac pharmacology at Imperial College, London, who reviewed the ethics of the U.K. legislation, says the team's methods were ethically sound. “It’s as good as or better than what we’ll do in the UK,” she tells Hamzelou, pointing out that the team did not destroy any embryos and produced a male child to minimize the chance that the mutated mitochondrial DNA could be passed to another generation.