Editing the human germ line: there is no undo button
Chinese scientists have completed the world’s first genetic modification of a human embryo. However, the troubling results have raised a red flag, and confirmed the fears of many scientists, that the scientific research investigating genetically modified embryos is at far too early a stage to be considered in humans.
Scientists are using a technology called CRISPR/Cas9, which uses enzymes to precisely cut DNA at specific locations, remove a gene, modify or repair it, and then re-insert it back into the DNA sequence. The CRISPR/Cas9 technology is relatively easy to use, and scientists reliably use it in research laboratories to genetically modify cells in a petri dish when studying the function of specific genes, and when modelling diseases.
Though a potentially strong therapeutic tool, an ethical debate has begun amongst scientists regarding whether this technology can (and should) be used to edit genes in the human germ line (the cells that can pass on genetic material through generations) in order to prevent disease. After all, we know the genetic basis of many human diseases, like the blood disorder thalassemia, or the neurodegenerative disorder, Huntington’s disease; if we can repair the mutation in a developing embryo, then we can prevent the disease from ever occurring, and effectively eradicate the disease. Easy, right? Wrong.
This week Chinese scientists published a paper in the journal Protein & Cell detailing their findings of genetically modifying human embryos. Using 86 non-viable embryos (the embryos contained a chromosomal abnormality that was incompatible with life) from a local fertility clinic, they applied the CRISPR/Cas9 technology to edit a gene (HBB) that causes a form of thalassemia when mutated. After the two-day editing job was complete, the scientists found that most cells did not show the edited gene. Even more frightening, they found many “off-target” mutations (i.e. mutations in genes other than HBB). These troubling results caused the scientists to halt the experiments and report their findings. Though this technology shows great promise, its use raises ethical concerns, and this study clearly shows there is a significant amount of research that needs to be done before this type of therapy could be used in humans.
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