Ever since scientists created the powerful gene editing technique Crispr, they have braced apprehensively for the day when it would be used to create a genetically altered human being. Many nations banned such work, fearing it could be misused to alter everything from eye color to I.Q.
Now, the moment they feared may have come. On Monday, a scientist in China announced that he had created the world’s first genetically edited babies, twin girls who were born this month.
The researcher, He Jiankui, said that he had altered a gene in the embryos, before having them implanted in the mother’s womb, with the goal of making the babies resistant to infection with H.I.V. He has not published the research in any journal and did not share any evidence or data that definitively proved he had done it.
But his previous work is known to many experts in the field, who said — many with alarm — that it was entirely possible he had.
“It’s scary,” said Dr. Alexander Marson, a gene editing expert at the University of California in San Francisco.
While the United States and many other countries have made it illegal to deliberately alter the genes of human embryos, it is not against the law to do so in China, but the practice is opposed by many researchers there. A group of 122 Chinese scientists issued a statement calling Dr. He’s actions “crazy” and his claims “a huge blow to the global reputation and development of Chinese science.”
If human embryos can be routinely edited, many scientists, ethicists and policymakers fear a slippery slope to a future in which babies are genetically engineered for traits — like athletic or intellectual prowess — that have nothing to do with preventing devastating medical conditions.
While those possibilities might seem far in the future, a different concern is urgent and immediate: safety. The methods used for gene editing can inadvertently alter other genes in unpredictable ways. Dr. He said that did not happen in this case, but it is a worry that looms over the field.
Dr. He made his announcement on the eve of the Second International Summit on Human Genome Editing in Hong Kong, saying that he had recruited several couples in which the man had H.I.V. and then used in vitro fertilization to create human embryos that were resistant to the virus that causes AIDS. He said he did it by directing Crispr-Cas9 to deliberately disable a gene, known as CCR₅, that is used to make a protein H.I.V. needs to enter cells.
Dr. He said the experiment worked for a couple whose twin girls were born in November. He said there were no adverse effects on other genes…