Science & Research

Threesome: How to Make One Baby From Three People


Geneticists are working on a fertilization method designed to eliminate genetic diseases

Photograph by UIG via Getty Images

Geneticists are working on a fertilization method designed to eliminate genetic diseases

Britain’s fertility regulator, the Human Fertilisation and Embryology Authority, has found broad public support for an in vitro fertilization technique that allows one baby to be created from the DNA of three people. Sorry, it’s neither kinky nor hot: The method is designed to eliminate genetic diseases like muscular dystrophy and mental retardation, which can be caused when children inherit abnormal mitochondrial DNA from their mothers.

Dr. Robin Lovell-Badge, a geneticist at Britain’s National Institute for Medical Research Council, was a member of the expert panel that evaluated the science. He talked with Bloomberg Businessweek to explain how it works; his answers have been condensed and edited.

How do you make a baby with DNA from three people?

First of all, the baby would still have the nuclear DNA of only two parents. Mitochondria, the organelles that produce cellular energy, contain their own DNA, which is separate from nuclear DNA. We inherit mitochondrial DNA exclusively from our mothers. The two techniques that are being researched to create one baby using the DNA of three people both involve transferring nuclear DNA out of the egg that contains abnormal mitochondria and into an egg from a donor mother who has healthy mitochondria.

What is the difference between the two methods?

The first involves transferring the nuclear DNA of a fertilized egg into another fertilized egg, from which the nuclear DNA has been removed. The second involves transferring the DNA of an unfertilized egg into a second unfertilized egg, and then fertilizing that second egg with the prospective father’s sperm.

The first method is somewhat easier because the nuclear DNA of a fertilized egg is neatly contained in a pronucleus, while the DNA of an unfertilized egg isn’t. The first method, however, is more controversial because some people define fertilized eggs as embryos and you start off with two embryos and have to destroy one.

Who’s behind this research?

A team in the U.K. has produced good results using the first method. Another team in the U.S. has successfully used the second technique involving unfertilized eggs in primates and in humans. The fact that the two groups are exploring different techniques may well have something to do with the politics of reproduction in the U.K. versus the U.S. In America, it would be very difficult to push the pronuclear transfer method because, yes, it would involve fertilized eggs.

Will the child inherit traits from all three parents?

No. The vast majority of the DNA—all of it that’s really important in determining characteristics, as normal, comes from the mother and father. Mitochondrial DNA only makes products required for the generation of energy—it doesn’t confer any personal characteristics at all, that we’re aware of.

How safe are these methods?

This is a double negative and I apologize, but we’ve concluded that there is no evidence that these methods are unsafe. There was nothing that scared us. … We did recommend that a few more experiments be done to provide reassurance because the amount of data that’s been published is good, but not enough, quite yet.

What legal hurdles still exist in the U.K.?

Regulations will have to be drafted and voted on by both houses of Parliament, but it’s possible that the technique could become legal toward the end of this year.

What about ethical hurdles?

The mitochondrial DNA does come from a donor woman. If the child born from the technique is a girl, if she has children, she will pass on the mitochondria—so this is really a form of germ-line genetical engineering. But I don’t think it’s a slippery slope. The methodology to deal with the mitochondria problem is very different from the methodology you’d have to use to manipulate genes within the nucleus.

How many children are born with abnormal mitochondria?

Roughly one in 10,000 people carry sufficient levels of abnormal mitochondria that it may cause disease in themselves or their children (though roughly one in 200 people carry abnormal mitochondria). It’s rare, but not that rare, and the diseases are truly horrible.

Cwinter
Winter is a reporter for Bloomberg Businessweek in New York.

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