Though the Chinese failed, some researchers worry the result of gene editing could be the birth of babies whose every cell has been altered by scientists in a rush to be first.
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 that 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.
Scientists in China report that they already tried it, and the experiment failed.
The Chinese researchers did not plan to produce a baby — they used defective 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 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 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 Dr. George Daley, a stem-cell researcher at Harvard, referring to in vitro fertilization. “This is an unsafe procedure and should not be practiced 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.”
Some researchers worry 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.
Gene editing uses a method called CRISPR that has rapidly become a research stalwart. It exploits a system that bacteria use to protect themselves from viruses and allows researchers to cut out selected genes and insert new ones.
A pressing question, said Rudolf Jaenisch, an MIT biology professor, is why anyone would want to edit the genes of human embryos to prevent disease. Even in the most severe cases, involving diseases such as Huntington’s in which a single copy of a mutated gene inherited from either parent is enough to cause the disease with 100 percent certainty, editing poses ethical problems.
Because of the way genes are distributed in embryos, when one parent has the gene, only half of the parent’s embryos will inherit it. With gene editing, the cutting and pasting have to start immediately, before it is possible to know if an embryo has the Huntington’s gene. That means half the edited embryos would have been normal and their DNA forever altered for no reason.
“It is unacceptable to mutate normal embryos,” Jaenisch said. “For me, that means there is no application.”