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Salk Scientists Propose New Mitochondrial Disease Fix

San Diego researchers have discovered a way to cut bad mitochondrial DNA out of mouse embryos. But they say ethical debate is needed before ever trying the technique in humans.

Researchers at the Salk Institute in La Jolla have discovered a way to cut bad mitochondrial DNA out of mouse embryos.

In theory, their technique could be used to prevent deadly mitochondrial diseases in humans, but experts say making heritable changes to human DNA raises major ethical concerns.

Photo by David Wagner

Juan Carlos Izpisua Belmonte discusses mitochondria in his lab at the Salk Institute, April 21, 2015.

Mitochondria power all the cells in your body. They're inherited maternally, and when mothers pass mutated mitochondria down to their children, the results can be devastating. Children with severe forms of mitochondrial disease often don't live past childhood.

In recent years, scientists have developed a procedure aimed at helping mothers who carry faulty mitochondria conceive children free of disease. The approach is controversial, in part because it uses parts of a healthy egg donated by another woman, and would produce children genetically related to three different people.

U.K. lawmakers voted in favor of so-called "three-parent" in-vitro fertilization earlier this year. Things have moved slower in the United States, as experts debate whether modifying human embryos to this extent could ultimately lead to designer babies.

Now, the "three-parent" fix has competition. In a paper published Thursday in Cell, the Salk Institute's Juan Carlos Izpisua Belmonte and his colleagues have shown how to directly cut specific strands of mitochondrial DNA out of mice embryos. No donor needed.

Izpisua Belmonte said if it works in humans, it could be a simpler way to prevent mitochondrial diseases.

"Clinics who do in-vitro fertilization on a daily basis can implement and adapt on top of what they normally do," he said.

Evan Snyder, a professor at the Sanford-Burnham Medical Research Institute, was not involved with the Salk research. As an FDA committee chairman, he reviewed "three-parent" in-vitro fertilization (he prefers the term "nuclear transfer").

Snyder said that if Izpisua Belmonte's technique holds up in further research, it could shift the debate.

"If this worked as nicely as the paper would suggest, this would be a technique that supplants nuclear transfer," Snyder said.

The study's first authors, Alejandro Ocampo and Pradeep Reddy, said all that's required is one injection of a molecule that makes precise cuts in mitochondrial DNA, like a pair of scissors. But the researchers said more studies are needed in animals and human cells before using those scissors in people.

Izpisua Belmonte said an ethical debate on editing human DNA is also needed.

"These diseases have no cure, and the only way to prevent their transmission is through these types of technology," he said. "Society needs to decide what should be done, and what not."

On Wednesday, Chinese researchers published the first reported use of genetic editing in human embryos. The fact that such work is already being done "reinforces the call for caution and for not proceeding further at this time," Snyder said.

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