He Jiankui of the Southern University of Science and Technology in Shenzhen said he changed the embryos for seven couples during their fertility treatments.
A Chinese scientist at the centre of a controversy over what he claims are the world's first genetically edited children has apologised for the result being leaked.
This is because it is said that DNA changes can pass to future generations and it risks harming other genes. The statement said that He has been on unpaid leave from the university since February, and that the Department of Biology's academic committee believes the researcher's conduct "has seriously violated academic ethics and codes of conduct".
For six questions that remain regarding He's contentious claimed scientific breakthrough, including a look at He's next potential moves and the impact this could have on the genome-editing field as a whole, see a report from Nature. "I feel proudest, because they had lost hope for life", He said, when challenged by several peers at the conference (live stream below).
The MIT Technology Review provided further details of the gene-editing tool, CRISPR, which looks to eliminate a gene called CCR5.
Chinese Vice Minister of Science and Technology Xu Nanping told state broadcaster CCTV that his ministry is strongly opposed to the efforts that reportedly produced twin girls born earlier this month. 'This would be a highly irresponsible, unethical and risky use of genome editing technology.
The reports fall in the grey area between attempts to cure diseases, and the dreaded "designer baby" scenario, where humans could be modified for benefits unrelated to health (potentially expanding to include intelligence, aesthetics and more). "This work reinforces the urgent need to confine the use of gene editing in human embryos to settings where a clear unmet medical need exists".
"This work is a break from the cautious and transparent approach of the global scientific community's application of the CRISPR-Cas9 for human germline editing". He is expected to present his findings on Wednesday at the Second International Summit on Human Genome Editing in Hong Kong.
And American biochemist David Liu - a co-inventor of the CRISPR/Cas9 technology that He said he used to alter the gene - said the procedure was unnecessary. An American scientist, Michael Deem of Rice University, also worked on the project.
"This is probably the worst gene you would choose" to test in pregnancy because it doesn't fix a disease the children were destined to get, said Shoukhrat Mitalipov of the Oregon Health & Science University, who in laboratory-only experiments studies how to repair gene defects in embryos.
Edit the genes happened in one of the stages of in Vitro fertilization. He had also previously spoken with the Associated Press about his study, which he says resulted in twin girls born with the first genomes edited by man.
Robin Lovell-Badge, a scientist from the Francis Crick Institute in London, said: "He obviously thought he was doing a good thing".
"All of us here at this conference are struggling to figure out what was done and also whether the process was done properly", she said. The CCR5 gene, for example, affects the functioning of white blood cells and a person's vulnerability to the West Nile virus. "And I'm willing to take the criticism for them".