No extra mutations in modified stem cells, study finds

The ability to switch out one gene for another in a line of living stem cells has only crossed from science fiction to reality within this decade. As with any new technology, it brings with it both promise—the hope of fixing disease-causing genes in humans, for example—as well as questions and safety concerns. Now, Salk scientists have put one of those concerns to rest: using gene-editing techniques on stem cells doesn't increase the overall occurrence of mutations in the cells. "As cells are being reprogrammed into stem cells, they tend to accumulate many mutations," says Mo Li, a postdoctoral fellow in Belmonte's lab and an author of the new paper. "So people naturally worry that any process you perform with these cells in vitro—including gene editing—might generate even more mutations."