On Monday, a highly unusual announcement shocked the scientific community: A Chinese scientist claimed he had edited the DNA of twin baby girls, Lulu and Nana, who he said had been born “crying into the world as healthy as any other babies” a few weeks ago.

A physicist by training, He Jiankui of Southern University of Science and Technology of China told the Associated Press that embryos from seven couples who underwent in vitro fertilization had been edited. He used a tool called CRISPR to disable a gene that allows HIV to infect cells, with one pregnancy resulting thus far.

The explosive announcement was made through a press interview and videos posted online by He. It came on the eve of an international summit dedicated to discussing the emerging science and ethics around powerful tools that give scientists unprecedented potential to tweak traits and eliminate genetic diseases — but that have raised fears of “designer babies.”

‘You have to talk about the ethics of genome-editing’

According to a description of the experiment posted online, He created embryos from couples with an HIV-infected father. The use of the technology immediately raised questions from ethicists since there are other ways to prevent HIV transmission to a fetus, and many think that the first applications of gene-editing should be reserved for diseases that are truly incurable. In the video, He said that only a single gene had been changed by the editing procedure, but gene-editing is known to introduce unintended genetic effects that could raise concerns, either for the children themselves or the human gene pool if the children grow up to pass on their genes.

The public announcement was highly unconventional, with no supporting data provided to verify the claims and no submission to the traditional process of peer review. It raised deep questions for scientists about whether traditional oversight channels were followed, as well as what to believe about the experiment and the results, although He posted an ethical approval form for the process on his website.

He did not respond to attempts to reach him by email and phone.

“I think this just shows the time is now that you have to talk about the ethics of genome-editing, because the world may not wait,” said Insoo Hyun, a bioethicist at Case Western Reserve University. “We don’t know how much of this is true or verified. These are all kinds of ... rumors at this point ... but in terms of scientific and medical rationale, I don’t think there is one.”

Shock from the scientific community

Scientists who had just landed in Hong Kong for the international summit on gene editing said the news took them by surprise.

“If it’s true as reported then it’s an extremely premature and questionable experiment in creating genetically modified children,” said Jeffrey Kahn, director of the Johns Hopkins Berman Institute of Bioethics. “There’s much to understand and discuss about oversight or lack thereof.”

Matthew Porteus, a pediatrician and stem cell scientist at Stanford University, said that the announcement highlights the weaknesses of the current regulatory system. “This is not the way I would like to see science advance. I have serious concerns,” Porteus said.

Southern University of Science and Technology, the institution where He is currently on unpaid leave, released a statement condemning the experiment, saying the university was “deeply shocked” by the news and had called an emergency meeting. The research was conducted off-campus, and the university was unaware of the project, according to the statement.

The university’s biology academic committee “believes that Dr. Jiankui He’s conduct ... to edit human embryos has seriously violated academic ethics and codes of conduct.”

In 2002, claims that a cult had created a cloned human baby caused a media firestorm. The claims were unverified, but they amplified ethical discussions about the possibility and triggered calls for banning human cloning.

“Coming on the eve of the second international summit on genome editing, this announcement looks like a cynical attempt to seize headlines,” said Pete Mills, assistant director of the Nuffield Council on Bioethics. “If the claims are true, it is a premature, inexplicable and possibly reckless intervention that may threaten the responsible development of future applications of genome editing.”

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