Confirming rumors that had been spreading since last month, Chinese scientists have reported they have modified human embryos genetically.
Obviously there are ethical implications of such endeavors and the debates have been raging since the rumors started. I’m setting those aside for a moment and looking at the news.
In the paper, researchers led by Junjiu Huang, a gene-function researcher at Sun Yat-sen University in Guangzhou, tried to head off such concerns by using ‘non-viable’ embryos, which cannot result in a live birth, that were obtained from local fertility clinics. The team attempted to modify the gene responsible for β-thalassaemia, a potentially fatal blood disorder, using a gene-editing technique known as CRISPR/Cas9. The researchers say that their results reveal serious obstacles to using the method in medical applications.
The ones for such editing in embryos could have beneficial because it could eradicate devastating genetic diseases before a baby is born. Others say point out the dangers because the genetic changes to embryos, known as germline modification, are heritable, they could have an unpredictable effect on future generations.
The technique used by Huang’s team involves injecting embryos with the enzyme complex CRISPR/Cas9, which binds and splices DNA at specific locations. The complex can be programmed to target a problematic gene, which is then replaced or repaired by another molecule introduced at the same time. The system is well studied in human adult cells and in animal embryos. But there had been no published reports of its use in human embryos.
Huang’s group studied the ability of the CRISPR/Cas9 system to edit the gene called HBB, which encodes the human β-globin protein. Mutations in the gene are responsible for β-thalassaemia.
Their results were far from positive. The team genetically tested 54 of the 71 surviving embryos. Of these only 28 were successfully spliced, and that only a fraction of those contained the replacement genetic material.
“If you want to do it in normal embryos, you need to be close to 100%,” Huang said. “That’s why we stopped. We still think it’s too immature.”
There were also a high number of ‘off-target’ mutations possibly introduced by the CRISPR/Cas9 complex acting on other parts of the genome. This is one of the main safety concerns surrounding germline gene editing because these unintended mutations could be harmful. The rates of such mutations were much higher than those observed in gene-editing studies of mouse embryos or human adult cells.
So, we are still far away from selective genetic modifications and biopunk is still just sci-fi, but this is just the beginning. I think the experiments will continue alongside the ethical concerns and debates and in a decade or so there will be more successful modifications. A Chinese source said that at least four groups in China are pursuing gene editing in human embryos.