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takyon writes:

A team of researchers led by Junjiu Huang at the Sun Yat-sen University in Guangzhou have reported human germline modification using CRISPR:

In a world first, Chinese scientists have reported editing the genomes of human embryos. The results are published in the online journal Protein & Cell and confirm widespread rumours that such experiments had been conducted — rumours that sparked a high-profile debate last month about the ethical implications of such work.

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.

[...] A Chinese source familiar with developments in the field said that at least four groups in China are pursuing gene editing in human embryos.

While some embryos were successfully edited, the use of CRISPR/Cas9 was not nearly as reliable as desired:

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%," Huang says. "That's why we stopped. We still think it's too immature."