A Chinese scientist has presented the results of a study in which he claims to have helped make the world's first genetically edited babies.
Speaking at the second International Summit on Human Genome Editing in Hong Kong, Professor He Jiankui said the twin girls, born this month, had their DNA altered as embryos to render them resistant to HIV and AIDS.
The veracity and ethicality of his claims have been questioned by the scientific community, with many calling the secretive nature of his research and the experiment itself 'monstrous'.
At the summit, He said that the trial had been paused, following international outcry over the highly controversial procedure.
'Willing to take the criticism'
Professor He's study has not undergone a peer review and thus his claims are unverified.
A number of institutions linked to the study, including a hospital, have denied any involvement, and the Southern University of Science and Technology in Shenzhen where Professor He is said to have conducted his research said it was unaware the project and plans to launch an investigation.
However, the geneticist said he used gene-editing tools to make the twins, called 'Lulu' and 'Nana'.
In an Associated Press report, Professor He claims to have eliminated a gene called CCR5 to make the girls resistant to HIV should they ever come into contact with the virus.
"I understand my work will be controversial - but I believe families need this technology and I'm willing to take the criticism for them," he told AP, going on to say that his work is about creating children that are immune to disease, rather than making designer babies with bespoke hair colour and other physical and mental attributes.
There has been much furore over the concept of 'designer babies' - the idea that parents may choose to manipulate the genetic structures of their children to suit their personal preferences.
While technically possible, the ethics of the matter remain blurry, with some opponents suggesting that more measures and checks are needed before it can be allowed.
Some scientists have suggested that if He's claims are true, by experimenting on healthy embryos without justification the Professor has overstepped the mark.
Scientists say baby gene editing may one day be justifiable, but that more checks and measures are needed before allowing it.
At present the risks involved in genetically editing an embryo are immense, with off-target mutations, capable of causing genetic problems early and later in life, including the development of cancer.
While gene editing may one day lead to a world without hereditary diseases by deleting or changing troublesome genetic coding in embryos, there are worries about the effects on future generations.
Experts are concerned that meddling with an embryo's genome may harm not only the individual but many generations of offspring that inherit the same changes.
Many countries have put laws in place to prohibit genome editing in embryos, although scientists are allowed to conduct gene editing research on discarded IVF embryos, as long as they are not used to make a baby.
Some are concerned, however, that He's study may cause a knock-on effect that leads to an overall suppression of interest in genetic editing.