Leading scientists have raised concerns over a Chinese professor's claim that he helped make the world's first gene-edited babies.
He Jiankui, a professor at the Southern University of Science and Technology in Shenzhen, claims to have gene-edited twin girls born earlier this month, altering their DNA to make them resistant to HIV.
Speaking at a human genome summit in Hong Kong, Mr Jiankui defended his work after facing a public backlash, saying he was "proud".
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Mr Jiankui failed or refused to answer many questions at the conference, including who funded him, how did he ensure that participants understood the potential risks and benefits, and why did he keep his work secret until after it was done.
Organisers of the summit branded his work "irresponsible", and members of the scientific community have condemned the act.
Gene-editing is highly controversial because the changes can be inherited and could go on to harm other genes. It is banned in many countries.
He Jiankui, centre, takes part in a question and answer session in Hong Kong. Image: Getty
David Liu of Harvard and MIT's Broad Institute, the inventor of a variation of the gene editing tool, said: "I feel more disturbed now.
"It's an appalling example of what not to do about a promising technology that has great potential to benefit society. I hope it never happens again."
China's National Health Commission has ordered local officials in Guangdong province to investigate Mr He's actions, and his employer, Southern University of Science and Technology of China, is also investigating.
Mr Jiankui's claim has not yet been confirmed by experts.