In a world's first, Chinese scientists have reported "editing" the genomes of human embryos. The results confirm widespread rumours that such experiments had been conducted in China.
These rumours sparked a high-profile debate recently about the ethical implications of such work, the scientific journal Nature reported, citing the study that first appeared in the journal Protein & Cell.
In the paper, researchers led by Junjiu Huang, a gene-function researcher at Sun Yat-sen University in Guangzhou, used "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 I-thalassaemia, a potentially fatal blood disorder using a gene-editing technique known as CRISPR/Cas9.
"I believe this is the first report of the gene-editing technique applied to human pre-implantation embryos. The study is a landmark one as well as a cautionary tale," said George Daley, stem-cell biologist at Harvard Medical School in Boston.
Some say that gene editing in embryos could have a bright future because it could eradicate devastating genetic diseases before a baby is born.
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Others say such work crosses an ethical line. The technique used by Huang's team involves injecting embryos with the enzyme complex CRISPR/Cas9, which binds and splices DNA at specific locations.
Huang and his colleagues studied the ability of the CRISPR/Cas9 system to edit the gene called HBB, which encodes the human I-globin protein.
Mutations in the gene are responsible for I-thalassaemia. The team injected 86 embryos and then waited 48 hours, enough time for the CRISPR/Cas9 system and the molecules that replace the missing DNA to act -- and for the embryos to grow to about eight cells each.
Of the 71 embryos that survived, 54 were genetically tested. This revealed that just 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 percent. That is why, we stopped. We still think it is too immature," Huang noted.
According to Huang, the paper was rejected by journals Nature and Science, in part because of ethical objections.
Still, he maintains that the embryos allow for a more meaningful model -- and one closer to a normal human embryo -- than an animal model or one using adult human cells.
A Chinese source familiar with developments in the field said that at least four groups in China are pursuing gene editing in human embryos, Nature concluded.