Before volunteering for a landmark medical experiment, Carlene Knight, who was born with a rare genetic eye disease, couldn't even maneuver around the call center where she works using her cane. Now her vision is clearer and brighter and has improved enough for her to make out doorways, navigate hallways, spot objects and even see colors. She is one of seven patients with a rare eye disease who volunteered to let doctors modify their DNA by injecting the revolutionary gene-editing tool CRISPR directly into cells still in their bodies. Earlier experiments had removed cells from patients' bodies, edited them in the lab and then infused the modified cells back into the patients. The current results are so promising that the researchers have gotten the go-ahead to move on to the next group of patients. Leber congenital amaurosis is caused by a genetic mutation that disables crucial cells in the retina, so patients progressively lose vision that usually renders them legally blind.

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