Although ethicists have come out in droves against genetic engineering at the level of a fertilized egg, some say the serious nature of these incurable diseases and the function of mitochondrial DNA should make this case of genetic engineering an exception.
"For these diseases that are very debilitating or devastating it makes sense," said Art Caplan, director of the Center for Bioethics at the University of Pennsylvania.
Starting with James Watson, who helped discover DNA's double helix, Caplan said geneticists often speak against "germ-line" engineering -- meaning genetically manipulating sperm, eggs or zygotes to change a human being.
"As recently as 2000 we had a large number of genetic experts saying, 'Don't do that,'" said Caplan, speaking about an Asilomar Symposium on Science, Ethics and Society where 247 scientists signed a position statement against it.
But Caplan argues in the case of mitochondrial DNA, "There's no intent here to interfere with the key genes that make us who we are. We're in the battery pack of the cell.
"I also think there's a little bit of coyness about it. Someone donating mitochondria. Is that person a third parent? I don't think so," said Caplan. "I don't think this is a big issue."
Not all agree.
David Prentice, a member of the lobbying organization Family Research Council, argued that replacing mitochondrial DNA was no different than other genetic engineering efforts.
"There are significant ethical concerns with this technique," said Prentice. "It involves cloning and germline genetic engineering of humans, requires destruction of young human embryos to create the recombined embryo, and is a eugenic technique that manufactures children."
Whatever the merits or disadvantages, both Prentice and Caplan agree that the technique would be legal in the United States.