The three-parent baby system may put babies at risk of serious illness.

We know of one case that doesn’t seem to work. When a baby is born from a fetus, the PGT states that 12% of the mother’s “bad” mtDNA is present. But when the baby was born, the rate was about 50%. This baby has many symptoms, including abnormal brain development, behavioral problems, and signs of a brain hemorrhage.

Only a few babies have been born after using PGT to diagnose mitochondrial disease, so again it’s hard to draw conclusions. The French center that pioneered the treatment and has been offering it since 2006 recently reported that only 29 babies had been born this way, Hendrikx said. In the last 10 years, his center has only been used to deliver four or five babies. And, as MRT reverses, there is a chance that children who are disease-free at birth may become sick as they grow.

“It’s scary,” Hendrikx said. “We also need to monitor babies born after PGT because this change may be happening there as well.”

A risky option?

Meanwhile, what does it mean for the MRT? Although the Newcastle group plans to continue the trial, others say that, at least for the time being, we should stop using MRT for mitochondrial disease and instead study it in people without these diseases, for example with infertility.

Mazur himself refuses to use MRT for mitochondrial disease. And Hendrix says the risk is too high for him — with a 20% risk of relapse, he says there’s no way the ethics committee at his institute would allow MRT to be used for mitochondrial disease.

Mertz said she has never been a fan of the MRT trials. Scientists already knew that the tests would never be without risk and would involve wasting perfectly good donor eggs and embryos. “You end up presenting patients with an option that is more dangerous than the alternative,” she says.

Experimental treatments like MRT help reinforce the idea that it’s important for parents to have a genetic connection to their children, Mertz says. “Wouldn’t it be wise to question whether that genetic link is so important if the price you pay is dangerous for your child’s health?” she asks. Parents can avoid all the risks that come with MRT by choosing to use donated eggs instead of their own or, for example, adopt a child.

In the meantime, clinics that offer MRT should update the information they provide “so people know this is a very dangerous risk they’re taking,” Mertes said. And both she and Pryor strongly believe that the treatment is only for those who “need” it, or at least want a genetic link to their children.

Mitalipov, like himself, is confident that scientists will finally find a solution to the return of mitochondria. “We just have to figure out why,” he said. “No clue yet… but give us time.”