A Potential But Controversial Fix For Genetic Disease

Newborn monkeys, Mito and Tracker, developed from embryos with transplanted DNA. i i

These healthy newborn monkeys, Mito and Tracker, developed from embryos containing transplanted DNA. They are named after the dye 'mitotracker' used for imaging mitochondria in cells. Oregon National Primate Research Center at OHSU hide caption

itoggle caption Oregon National Primate Research Center at OHSU
Newborn monkeys, Mito and Tracker, developed from embryos with transplanted DNA.

These healthy newborn monkeys, Mito and Tracker, developed from embryos containing transplanted DNA. They are named after the dye 'mitotracker' used for imaging mitochondria in cells.

Oregon National Primate Research Center at OHSU
A fertilized monkey egg undergoes a nucleus transplant.

A fertilized monkey egg undergoes a nucleus transplant. Oregon National Primate Research Center at OHSU hide caption

itoggle caption Oregon National Primate Research Center at OHSU

Scientists in Oregon have developed a technique that could be used to prevent certain genetic diseases. They've demonstrated it in monkeys and are anxious to try it in people. The technique raises ethical questions, however, because it makes a permanent genetic change not just in an individual, but in all generations that follow.

The technique involves an unusual set of genes in the human body. Most of our genes are in our chromosomes, which are in the cell's inner sanctum, the nucleus. But 37 human genes are outside the nucleus. They are contained in tiny bodies called mitochondria, which float around in our cells. Mitochondria are the mini power plants for our cells. And mutations in the genes inside mitochondria can cause disease.

Shoukhrat Mitalipov and his colleagues at Oregon Health and Science University are trying to figure out how to treat this class of rare genetic diseases. They've been working with the eggs of rhesus monkeys. If you fix a genetic problem in an egg, you will fix it in all the cells the egg grows into — the whole animal.

"So, basically, we construct this experimental egg, which contains nuclear genes from one female, but mitochondrial genes from another female," he says.

In short, they can remove the nucleus from an egg that has defective mitochondrial genes, and put it into an egg that has healthy mitochondria. So the mother's chromosomes end up in an egg that has healthy mitochondria, albeit from a different female.

The technique worked quite well in monkeys, according to a study the journal Nature has published online. The researchers made this transfer with 15 eggs, fertilized them, and ended up with four baby monkeys.

"So what we showed is these manipulated eggs acted like normal eggs, and most importantly they resulted in births of healthy offspring," Mitalipov says.

The monkeys are only a few months old so far. It will take four or five years before the scientists know whether they are able to reproduce successfully. It could take even longer to notice any long-term health effects. But Mitalipov says he doesn't want to wait that long — he wants to try the technique in people.

To do that, he would need to convince the Food and Drug Administration that the technique is safe. And he will also have to deal with a key ethical issue. Art Caplan at the University of Pennsylvania says the issue is that modifying the genes in an egg doesn't merely affect one individual — the modification ends up in the eggs of the individuals, too.

"It goes on forever, because it's passed on from generation to generation," Caplan says.

This kind of manipulation is called "germ line" therapy, and it's been considered taboo. For one thing, if there are health risks, they will affect multiple generations. For another, it could open the door to genetically engineering a lineage of people with supposedly superior qualities. This is called eugenics, and many people find that repugnant.

"It does breach the principle: no germ line engineering," Caplan says. "It breaches a promise that many geneticists have made, that whatever else, they're not going down that road. I always thought that promise would be difficult to keep. This particular experiment shows why."

Caplan argues the egg manipulation in this case isn't seeking to make an improved person, just a healthy one. And he's OK with that.

But George Annas at Boston University is uneasy — both for ethical reasons and for practical ones.

"I don't think anything should be totally off the table, although this would be pretty extreme," he says. "I would probably have a presumption it shouldn't be done, and the burden of poof would be on the people who propose doing it: that it's safe, and that it's not going to create problems — not just for the children, but for the children's children."

Annas says it will take a lot more than just four apparently healthy baby monkeys to make that case.

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