Chinese scientists edit genes of human embryos, raising concerns

The experiment with human embryos was dreaded, yet widely anticipated. Scientists somewhere, researchers said, were trying to edit genes with a technique that would permanently alter the DNA of every cell so any changes would be passed on from generation to generation.

Those concerns drove leading researchers to issue urgent calls in major scientific journals last month to halt such work on human embryos, at least until it could be proved safe and until society decided if it was ethical.

Now, scientists in China report that they tried it.

The experiment failed, in precisely the ways that had been feared.

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The Chinese researchers did not plan to produce a baby – they used defective human embryos – but did hope to end up with an embryo with a precisely altered gene in every cell but no other inadvertent DNA damage. None of the 85 human embryos they injected fulfilled those criteria. In almost every case, either the embryo died or the gene was not altered. Even the four embryos in which the targeted gene was edited had problems. Some of the embryo cells overrode the editing, resulting in embryos that were genetic mosaics. And speckled over their DNA was a sort of collateral damage – DNA mutations caused by the editing attempt.

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“Their study should give pause to any practitioner who thinks the technology is ready for testing to eradicate disease genes during IVF.,” said George Q Daley, a stem cell researcher at Harvard, referring to in vitro fertilisation. “This is an unsafe procedure and should not be practised at this time, and perhaps never.”

David Baltimore, a Nobel laureate molecular biologist and former president of the California Institute of Technology, said, “It shows how immature the science is,” adding, “We have learned a lot from their attempts, mainly about what can go wrong.”

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But some researchers worry that this paper is just an initial sally and that attempts will continue with clinical applications in mind. They fear the result will be the birth of babies whose every cell has been altered by scientists in a rush to be first. This could happen well before researchers know enough about the consequences of editing genes, before they know how to edit safely and before society can debate if such procedures are even acceptable.