A three-parent baby born in Mexico.

Nature (and New Scientist) have been covering the developing story about a healthy baby boy born from genetic material supplied by three parents:

Researchers at the New Hope Fertility Center in New York City told New Scientist — which broke the news on 27 September — that they had conducted the procedure for a Jordanian couple, and that the baby boy was born in April. The team, led by John Zhang, is not due to present details until 19 October, at the American Society for Reproductive Medicine meeting in Salt Lake City, Utah, but it has published an abstract online with sparse information.

According to the abstract, the boy’s mother has a rare disease called Leigh’s syndrome, a neurological disorder caused by faulty mitochondria, the cell’s energy-producing structures. The couple lost two children to the disease before asking the clinic’s help.

In an attempt to create embryos without the mother’s faulty mitochondria, the clinic’s team transferred the nucleus of the mother’s egg cell to the egg of a donor with healthy mitochondria — a technique known as spindle transfer — and then fertilized it with the father’s sperm, the team reports in the abstract. Zhang’s team modified five embryos, one of which was implanted into the mother and survived to birth. That baby inherited nuclear DNA from both parents and mitochrondrial DNA from the donor.

[S]ome other researchers are troubled by Zhang’s announcement. “They just went ahead and did it,” says David Clancy, who studies mitochondrial biology at Lancaster University, UK. “The number of issues that are still unresolved — it’s just staggering.”

Among the unknowns is the possibility that the technique could transfer some diseased mitochondria from the mother into the donor egg along with the nucleus. According to Zhang’s abstract, 5% of the embryo’s mitochondrial DNA was carried over along with the mother’s nucleus — while mitochondrial DNA samples taken from the baby after birth varied from tissue to tissue and suggested a level of faulty DNA that was at most 1.6%.

More concerning to some researchers is the fact that Zhang’s procedure was performed in Mexico. Zhang told New Scientist that “there are no rules” in Mexico. Legal scholar Rosario Isasi at the University of Miami in Florida says that there are laws governing the manipulation of human genes –but she adds that they are badly worded and that there are exemptions that seem to be made for manipulations intended to cure deadly disease.

Isasi questions the wisdom of performing the procedure in Mexico, which has a reputation as attracting patients from elsewhere who seek unproven cures that are not allowed in their own countries, instead of a country such as Sweden, whose government closely regulates the clinical use of therapies. “You have all these negatives, and it’s not a place that can offer the scientists a high-tech environment,” says Isasi.

The clinic chose Mexico because it already had a branch there, New Hope spokesman Geoffrey Hawes told Nature. He declined to comment on whether the regulatory environment in Mexico played a part in the decision. “It’s off limits, we won’t comment on regulations,” he says.