DNA repair after CRISPR cutting not at all what people thought

Despite high hopes and high investment in CRISPR-Cas9 gene editing, scientists still have a lot to learn about how it works in humans.

In the latest example, University of California, Berkeley, scientists found that people’s assumptions about how cells repair the genome after the Cas9 enzyme snips DNA are wrong.

The discovery gives insight into why CRISPR-Cas9 gene editing works remarkably well in nearly every cell attempted, though not with equal success in all cells. And it could help researchers boost the efficiency with which cells insert new DNA into the genome – to replace a harmful mutation with the correct DNA sequence, for example – and generally tweak CRISPR-Cas9 editing to get the desired outcome.

“If you want to treat sickle cell anemia, your chances of success are inextricably tied to the efficiency with which you can replace the mutated sickle cell gene with the correct one,” said UC Berkeley postdoctoral fellow Chris Richardson, first author of a paper describing the findings. “If you harvest a million cells from a patient and you have 10 percent insertion rate, that is not as good as if you have 30 to 40 percent. Being able to manipulate those cells to increase the frequency of


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