Researchers Edit Genome Of Human Embryo For First Time, Generating Both Excitement and Ethical Backlash

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Chinese scientists working at Sun Yat-sen University in Guangzhou, China have successfully edited the genome of a human embryo for the first time. The results of the study were published in the online journal of Protein & Cell, and the findings were subsequently covered by Nature, MIT Technology Review, and a myriad of other notable scientific publications.

In the experiment, researchers were attempting to establish the feasibility of using a technique known as CRISPR/Cas9 to modify the genome of a human embryo. Researchers have been searching for an effective means of permanently editing human genomes since the late 90s. Various technologies came before CRISPR, but the excitement around the CRISPR method has become feverish because it offers a cheap, reliable way of introducing foreign genetic material into a DNA strand with a high degree of precision and permanent effects. In the last three years, CRISPR has been used to modify the genomes of yeast cells, flies, zebra fish, plants and mice. In a recent MIT study, researchers used CRISPR to cure mice with a rare genetic liver disorder by removing and replacing the underlying problems in the genome. CRISPR had also been used successfully to edit genomes in cultured human cells, but until now CRISPR technology had not been used on a human embryo.

The researchers behind this study were interested in finding out if CRISPR could be used to remove mutations associated with genetic disorders in humans prior to birth. To test this, the team edited the DNA of fertilized eggs that were found to have a genetic defect that causes beta-thalassemia, a group of inherited blood disorders. Using CRISPR, the team removed the problematic section of DNA and replaced it with healthy DNA. To address ethical concerns, the team only used fertilized eggs that were non-viable, but that were still capable of going through the early stages of embryonic development. The scope of the study was only to see if researchers could remove and replace harmful sections of DNA in a human embryo.

The team attempted the procedure on 86 embryos at the point that they were still in single-cell stage of development. Researchers thought that if they removed and replaced harmful genetic mutations while the embryo was still a single cell, that all subsequent cells would have the corrected genetic material. After 48 hours, researchers analyzed the 86 embryos, which had all multiplied into eight-cell organisms at that point. The results were disappointing; of the 86 embryos only 71 had survived the 48 hours. Within that group, 54 were genetically tested before researchers called off the experiment. In that group of 54, only 28 had its DNA spliced in the correct location, and just a fraction of those also had the replacement genetic material successfully introduced.  Junjiu Huang, the lead researcher, explains,  “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.”

Despite the setback, the study marks the first time that scientists have attempted to edit the genome of a human embryo, and is therefore an important study. Beyond the ethical concerns over using human embryos in research, many scientists are calling for a temporary ban on embryonic genome editing because those genetic changes then become inheritable and so they could potentially be permanently introduced into the general public.


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