Chinese scientists edit genes of human embryos

Chinese scientists report the first-ever genetic modification of human embryos using the CRISPR/Cas9 gene-editing technique, confirming rumours that these highly controversial experiments were underway.

Although the technique has been used extensively in adult human cells and animal embryos, this is the first time the CRISPR/Cas9 system has been used to alter the genes of human embryos. It was used to take out a faulty gene that causes the inherited blood disorder beta-thalassaemia and replace it with a working version of the gene.

Last month, scientists writing in the journals Nature and Science called for an international moratorium on the use of this so-called 'germline modification' of humans - in which all the cells, including sperm and eggs - are altered (see BioNews 795). They fear that any unintended effects of the technique would be passed down through the generations and leave an indelible mark on the human gene pool. There are also concerns that the practice could lead to 'designer babies' with genes for traits such as intelligence, athletic ability, or even hair and eye colour.

'This news emphasises the need for an immediate global ban on the creation of GM designer babies,' Dr David King, director of Human Genetics Alert, told The Telegraph. 'It is critical that we avoid a eugenic future in which the rich can buy themselves a baby with built-in genetic advantages.'

The research was led by Dr Junjiu Huang of Sun Yat-sen University in Guangzhou, who published the research in the online journal Protein and Cell. Huang told Nature News that the paper had been rejected by both Nature and Science because of ethical concerns. Huang and his team used non-viable human embryos that had been fertilised by two sperm, which ensured that they would only go through the first few stages of embryo development and would never result in live births.

They applied the technique to 86 embryos and left them for 48 hours to grow into eight-celled embryos. Of these, 71 survived and 54 of these were genetically tested. Only 28 contained the healthy version of the gene but only in some of their cells. Because of this low success rate, Huang said his team discontinued their research. 'If you want to do it in normal embryos, you need to be close to 100 percent. That's why we stopped. We still think it's too immature.'

More significantly, there were a surprising number of 'off-target' mutations in which the versions of the inserted gene appeared in parts of the genome where they shouldn't. This is one of the principal concerns of the use of the gene-editing technique in human embryos. The rate of these mutations was much higher than those seen in CRISPR/Cas9 studies involving adult cells or mouse embryos.

Despite calls to end experiments involving genetic modification of human embryos, it is thought that this is taking place in at least four labs in China. And one US genetics laboratory, on condition of anonymity, told MIT Technology Review that it too was using the gene-editing technique on human embryos rejected by IVF clinics.