Testing genetically modified mitochondrial DNA in people is now ethically permissible, but the scientific community is concerned about how gene manipulation will impact society, biology experts said Wednesday.

A new report from the Institute of Medicine, now part of the National Academies of Sciences, Engineering and Medicine, says clinical investigations involving mitochondrial replacement techniques – using healthy mitochondria from a donor egg– could be the first step to preventing the transmission of mitochondrial genetic diseases from mother to child. Testing is not expected to begin immediately because the U.S. Food and Drug Administration still has to evaluate the report, said Jeffrey Kahn, chair of the institute’s board on Health Sciences Policy.

According to the report, the replacement technique would allow women with mitochondrial DNA, or mtDNA, diseases to have genetically related children who do not have the condition.

Mitochondria are organelles in cells that are responsible for producing energy. When not enough energy is produced by the mitochondria, cells can weaken, be injured or die off, damaging the brain, heart, liver, skeletal muscles, kidney and the endocrine and respiratory systems, according to the United Mitochondrial Disease Foundation. The diseases vary, but common symptoms include seizures, heart problems, muscle weakness, fatigue and developmental delays.

Although altering genetic material is worrisome, the modifications being suggested are restricted to an egg’s mitochondrial DNA and not nuclear DNA, said Kahn.

“You’re not actually able to go in and genetically modify nuclear DNA,” said Kahn, who is also deputy director for Policy and Administration at the Johns Hopkins Berman Institute of Bioethics and the founding president of the Association of Bioethics Program Directors. “Gene editing would let you do that, but that’s not what this technology is. This is really a manipulation of an egg or fertilized egg. It’s very different.”

Nuclear DNA controls a person’s physical or behavioral characteristics and determines how people become who they are, said Philip Yeske, a science officer with the United Mitochondrial Disease Foundation– an advocacy organization for people suffering from mitochondrial diseases. Yeske said the replacement technique will have a “huge impact” on affected women who want to have children.

Mitochondrial DNA diseases can affect both sexes, but they are transferred to offspring through women because the mitochondria in sperm is not passed on during fertilization. While the diseases primarily affect children, adult-onset cases are becoming more common.

“This is about an unmet medical need for this very small slice of the population,” said Yeske. “It’s not about selecting for intelligence or hair color.”

One in 5,000 women are affected by a mitochondrial DNA disease, said Yeske in a phone interview.

Still, critics are concerned that clinical testing of mitochondrial replacement will open the door to gene editing to try to produce a superhuman, said Marcy Darnovsky, executive director of the Center for Genetics and Society, a public affairs organization.

“It opens the fraught social question of going down the road to a new high-tech consumer-based eugenics and introducing completely new kinds of inequality in our already shamefully unequal world,” said Darnovsky in a telephone interview.

To prevent experimentation with gene selection, Darnovsky said the United States should adopt legislation that prohibits people from selecting specific traits.

“We would have a different political and social context in which we could look at mitochondrial techniques and see if they really are exceptions to the rule,” she said.

Despite the concerns, Kahn said it will be “years at the earliest” before any mitochondrial replacement techniques will be available for public use. Clinical testing can only be conducted if proper protocols and restrictions are met, such as being restricted to women who have been diagnosed with a very serious mitochondrial DNA disease and have a high risk of passing it along to their children, he said.

If successful, the technology will provide affected women with an unheard of opportunity, said Yeske.

“If these techniques are shown to be safe and efficacious, they should be offered as an option to the community,” he said. “It’s a small population, but I don’t know that we could put a value on that ability to have a genetically related child and not pass along a uniformly fatal disease.”