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'Three-Parent Babies' May Be Possible With Mitochondrial DNA Replacement

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Medical experts released a report Wednesday, advising that women with certain genetic diseases should be able to conceive children with the aid of a second mother.

The announcement will come as a relief to women who carry mitochondrial mutations that can cause severe problems for their children. Mitochondria are the structures that essentially serve as the kitchen of every cell, converting energy into "food" the cell can use. Mitochondria also contain their own DNA, just 37 of around 25,000 genes in the human genome. Yet, those 37 genes are critical to healthy offspring. 

In the proposed technique, a "third parent" — female donor — would provide her egg as well as healthy mitochondrial DNA. The mother's affected DNA would then be removed from her genome, and her nuclear DNA would be dropped into the egg. The mother would still provide the bulk of the DNA, and the remaining more than 20,000 genes. Finally, the father's sperm would fertilize the egg.

Although it's tempting to think of these hypothetical pregnancies as having three parents, the embryo would barely have any genetic information from the donor; only the special DNA needed to stave off mitochondrial diseases like Leigh Syndrome, which causes the loss of mental and movement abilities, progressing over time and eventually killing the child, typically before age seven. An adult with the disease may have less pronounced issues, but passing on those genes gives their child a dangerously high risk of severe disabilities.

Mitochondrial mutations are also responsible for a high rate of miscarriage, so this treatment could also help parents who have experienced multiple failed pregnancies.

The intervention was developed quickly, less than a year after scientists successfully altered the mitochondrial DNA of mouse blastocysts.

However, the process comes with a catch: the agency says any blastocysts conceived this way should only be implanted if they are male. This is because men can only pass down mitochondrial DNA for one generation; females, on the other hand, can pass it on indefinitely, putting future generations at risk should the mitochondrial intervention carry unexpected side effects.

The Center for Genetics and Society, which opposes genetic modification in human reproduction, expressed concern about the report. In a press release, executive director Marcy Darnovsky stated, "The procedure is very similar to cloning techniques, and carries some of the same risks."

She also echoed the concerns of many Americans who fear that any genetic modification of the human genome is a slippery slope toward "designer babies."

"It's important to realize that if the FDA were to approve these techniques, it would have few mechanisms for preventing what would essentially be 'off label uses,'" Darnovsky said. "One U.S. proponent of these techniques has already made it publicly clear that he would like to expand their use widely to fertility clinics. Their use could easily spin out of control."

The report, released by the National Academy of Science, Engineering and Medicine, was requested by the Food and Drug Administration (FDA). It was analyzed and compiled by a panel of experts and comes on the heels of the U.K.'s announcement that certain research may be carried out on human embryos. The full report can be read here.

Photo: Solis Invicti | Flickr

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