Scientists in China have genetically modified human embryos in a world first. The Chinese group used a genome editing procedure called Crispr to modify an aberrant gene that causes beta-thalassaemia, a life-threatening blood disorder, in faulty IVF embryos obtained from local fertility clinics. The team, led by Junjiu Huang at Sun Yat-sen University in Guangzhou, is the first to publish such work, confirming rumours that have been circulating for months that human embryos had been modified in China. The work is described in the journal Protein and Cell. Two prominent journals, Nature and Science, rejected the paper citing ethical objections, Huang said. Last month, researchers writing in Nature called for a global moratorium on the genetic modification of human embryos, citing "grave concerns" over the ethics and safety. They added that any therapeutic benefits were tenuous. Genetic modification of the DNA in human embryos would not only affect the individual but their children and their children's children and so on down the generations. That could halt the inheritance of genetic diseases that run in families, but it could also pass on unforeseen medical problems that the procedures may cause. One of the main safety concerns with genome editing is the risk of changes being made to healthy genes by accident. These so-called "off-target" edits happened far more than expected in Huang's study, suggesting that the procedure they used is far from safe.