Today a panel of scientists released a report recommending that the US Food and Drug Administration (FDA) approve testing for a medical procedure known as mitochondrial replacement, which could prevent dangerous genetic diseases in newborns. The procedure, already approved in Great Britain, still has a long way to go before final approval in the US.

A microscopic organ transplant

Though critics say it will send us down a slippery slope of "gene editing," there is in fact no gene editing involved in mitochondrial replacement. Instead, it's more like a microscopic version of an organ transplant.

Mitochondria are called "organelles" because they play an organ-like role in the cell. A bit like a miniature stomach, mitochondria break down molecules to provide energy for the entire body. Mitochondria are also the only part of the cell that contains DNA, other than the nucleus. Some biologists believe this is because mitochondria were once separate cells, absorbed in a process called endosymbiosis during a very early phase in cellular evolution, which nevertheless retained a shred of DNA over the billions of years since that merging.

Babies inherit mitochondria from their mothers, and any mutations in the mother's DNA will be passed down to her children, her grandchildren, and so on. About one in 5,000 births has a mitochondrial DNA mutation, and symptoms range from mild to extreme, including heart failure, dementia, and death. There are no known cures for diseases caused by mitochondrial DNA mutations.

In mitochondrial replacement, a donor provides mitochondria to the mother, replacing her damaged mitochondria. The mother's DNA remains unchanged, as does the donor DNA. There are several techniques for accomplishing this, but the result is an egg that contains donor mitochondria and the mother's nuclear DNA. With the help of healthy donor mitochondria, these problems will be solved—the child will not pass along damaged mitochondria to her children, and the disease is removed from the mother's germline permanently.

Once this egg is fertilized, the result is a child that technically has genetic material from three people. That said, Duke bioethicist Nita Farahany argues that the amount of DNA provided by the mitochondria is so small that it's a bit of a leap to say we're making children with three parents. It's more like you've got a baby with donor organelles in his or her cells.

Regulatory red tape

The report released today was requested by the FDA, which has been considering the merits of mitochondrial replacement for almost two years. The FDA asked the National Academies of Sciences, Engineering, and Medicine to convene a panel of scientists to weigh in on the ethics of proceeding with human trials on the procedure, which has already been tested in animals. The panel—with a number of caveats—said testing would be ethical.

The panel stipulated that once trials were complete, the procedure should be done initially on male embryos only. That way, if anything went wrong, the mitochondria would not be passed down to the next generation (remember, you inherit mitochondria from your mother). Despite the ethical reassurances, it appears the FDA is still reluctant.

NPR's Rob Stein wrote that the FDA's reaction to the recommendations was tepid at best:

The FDA ... praised the "thoughtful work" of the panel and said the agency would be "reviewing" the recommendations. But it noted that the latest federal budget "prevents the FDA from using funds to review applications in which a human embryo is intentionally created or modified to include" changes that could be passed down to future generations. As a result ... any such research "cannot be performed in the United States" at this time.

Mitochondrial replacement has already been approved in Great Britain. It may be many years before the panel's recommendations lead to clinical trials in the US, let alone medical treatments. But this report represents an important first step for parents who want to have children without fear that they will inherit the mitochondrial mutations of their mothers.