Researchers say that they have used a precise genome-editing technique called base editing to alter the genome of human embryos. The announcement has prompted excitement and caution from scientists and bioethicists. Many say that the work is an impressive step towards clinicians being able to fix disease-causing mutations in embryos. But others worry that the technology could be used to try to create embryos with traits such as superior intelligence.

Dieter Egli, a developmental cell biologist at Columbia University in New York City, and his colleagues posted their results on the bioRxiv preprint server on 1 June¹. The study, which was first reported by The New York Times, has not yet been peer reviewed

Previous studies had suggested that the use of a standard but less precise form of gene editing in embryos can cause the loss of the edited chromosomes — an effect that made the technology unusable in embryonic cells.