At first glance, the landmark experiments using CRISPR to correct a mutation in human embryos represent a breakthrough, since they demonstrated three key things: that CRISPR can delete the gene it’s supposed to in a viable embryo, that it can make the change in a way that causes all of an embryo’s cells to have it (when some embryo cells but not others have their DNA changed it’s called mosaicism and would be a problem), and that CRISPR can do this with few if any unintended edits, or off-target effects.
But when STAT spoke to the lead scientist, reproductive biologist Shoukhrat Mitalipov of Oregon Health and Science University, two days before his study was published in Nature, he had a different view on his experiment.
“The main finding,” he said unequivocally, is that the CRISPR’d embryos did not accept the “repair DNA” that the scientists expected them to use as a replacement for the mutated gene deleted by CRISPR, which the embryos inherited from their father. Instead, the embryos used the mother’s version of the gene, called the homologue.
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