Twin girls have allegedly been born in China after having their embryonic genetic code modified using CRISPR. Chinese researcher He Jiankui from the Southern University of Science and Technology claims to have turned off a gene called CCR5 to offer total protection against HIV, as well as smallpox and cholera.

The news, which has not yet been independently verified, has proven enormously controversial. Jiankui has allegedly switched off the gene in embryos for seven couples so far, though only one successful pregnancy has occurred. Editing embryos that lead to a full birth is heavily regulated in most countries, and has not previously been attempted.

Concerns have also been raised that this step could lead to genetic modification creating “designer babies”, selected for certain physical or behavioural traits. Another worry is that CRISPR technology is not yet proven to be wholly safe or without side effects, with worries that use of CRISPR could cause mutations in other genes.

Many scientists have reacted by pointing out that HIV is currently treatable using medication. At the moment, it is already possible to stop children from inheriting many serious diseased by screening IVF embryos before implanting them.

While verification of this news is currently underway, official documents do show that research of this type was cleared in Shenzhen.