Should parents edit their offspring’s genes, so as to ensure that the child does not grow up with an inherited disease or disorder? He Jiankui, an associate professor at Southern University of Science and Technology in Shenzhen, has done precisely that for a couple. He used gene-editing technology on a fertilised egg cell of the couple to make babies (twin girls born healthy last month) supposedly resistant to HIV. The husband being HIV-positive and the wife HIV-negative, it was in their interest to ensure their babies were not born with HIV. Jiankui claims he did this by disabling in their egg cell a gene that forms a protein doorway in the body to the HIV virus. The Chinese scientific establishment has raised several questions about the opaque manner in which Jiankui carried out the procedure, the risks he took and the inducements he offered to the couple. Researchers are alarmed about the risks involved, like unknowingly changing other genes or changing only the target gene in some cells while leaving the others unaltered. This can result in unexpected and harmful health effects later in life, such as cancer. Jiankui has been disowned by his varsity and barred from scientific activity, while an investigation has been launched into his experiments. But the outcry over the world’s ‘first gene-edited babies’ shows there is a minefield of ethical issues and unforeseen risks that the scientific community must confront before forging ahead.