Two babies from three parents: Mito and Tracker, baby rhesus macaque twins, are the first to have DNA from three parents–nuclear DNA from their mother and father, and mitochondrial DNA from a second female monkey, which they inherited through her donated egg.
“The technique that they used, transferring a chromosomal spindle to get new mitochondria to power the egg, seems completely ethical and defensible,” says Arthur Caplan, a bioethicist at the University of Pennsylvania. “But while this technique doesn’t have much use outside of fixing problems in the mitochondria, it does open the door a tiny bit on germline engineering.” Because it’s using a self-contained part of the cell, he notes that it’s not what people typically have in mind when they talk about tinkering with germline genetics. “But by cracking open the door, it puts the principle of never doing germline engineering into dispute.”
David Magnus, who heads Stanford University’s Center for Biomedical Ethics, agrees that most of society’s germline engineering concerns don’t apply in this case. But he does point out that the procedure would lead to, essentially, three parents instead of two, “making legal and social arrangements more complicated,” he says. “What happens if the mitochondrial donor decides, down the road, that she should have some parental rights to the offspring?”
This is, of course, getting way ahead of the science itself. Much more must be done before the procedure is approved. The new technique has only been applied in nine rhesus macaques, three of which became pregnant (one with twins)–a 33 percent success rate that appears to mirror that of regular in vitro fertilization in human patients. And since the seemingly healthy offspring have not yet reached reproductive age, Mitalipov and his colleagues don’t yet know whether the procedure has genetic implications they’ve not yet uncovered. The procedure will also need to be refined, tested in more than nonhuman primates and at other research facilities before human trials can begin. (The Oregon lab is known for very high success rates that other labs can rarely duplicate.)
Researchers in Britain, at the University of Newcastle upon Tyne, have reportedly done something similar in human embryos, but have yet to publish their results and would not comment on Mitalipov’s research.
The Oregon researchers believe they may be ready to apply for clinical trials in two to three years, but much depends on funding and government approval. “This points the way to a technique–it doesn’t provide a therapy,” says UC Irvine’s Wallace, who was the first researcher to discover disease-causing mutations in mitochondrial DNA. “It shows that the concept can work as one approach to treating mitochondrial DNA disease. And that’s an incredible advance, since we have very little to offer these families right now.”