The gene editing summit in Washington organised to discuss new techniques which enable researchers to alter human DNA shared an ethical concern about gene editing. The summit raised the doubt that it would be "irresponsible" to allow the creation of genetically altered humans. But they said basic research involving embryo gene editing should continue in order to improve understanding of human biology. As scientific knowledge advances and societal views evolve, they added, the clinical use of genetically modified embryos should be revisited on a "regular basis".

Three years ago scientists invented a new simple cut-and-paste system, called CRISPR-Cas9, for editing DNA. Scientists across the world immediately adopted this rapid, cheap and accessible tool in order to speed up their research. For patients with blood, immune, muscle or skin disorders it offers the hope that their faulty cells could be removed, tweaked in the lab and then re-implanted. But even if patients carrying a genetic disease were successfully treated, they would still be at risk of passing on that faulty DNA to their children. That's where gene editing in embryos comes in. Fix the error in a newly fertilised embryo and - in theory - it would provide a permanent genetic fix that would pass down the generations.

Earlier this year, in a world-first, scientists in China announced that they had carried out gene editing in human embryos. They were attempting to correct a gene that causes an inherited blood disorder, beta thalassemia. The laboratory experiments had very mixed results, showing this technology is still in its infancy. It was a key reason why leading science bodies decided to organise the first global summit on gene editing. None of the scientists at the Washington summit is remotely ready to take embryo gene editing into the clinic.