Monica Coenraads’ daughter has never spoken since she blurted out “duck!” while taking a bath soon before her first birthday, and has never walked. Chelsea lost the ability to hold her sippy cup and stopped responding when Coenraads played “can you touch your nose?” She cannot use her hands, and must be fed through a tube, all of which is tragically standard for girls with severe Rett syndrome, a brain disorder that usually strikes during toddlerhood and is caused by a genetic mutation.

It may seem unlikely, then, that such a devastating condition is near the front of the line of brain disorders that scientists believe might one day be treated with genome editing technologies such as CRISPR. By “treated,” they don’t mean just keeping a disease from getting worse. They mean reversing the damage and giving the brain a second chance: CRISPR would penetrate the brain of a patient who has lived with a disorder for years and repair the mutation that caused it, unleashing the brain’s capacity of neuroplasticity to weave new circuitry, grow new neurons, or otherwise do right what it did wrong when the mutant gene called the shots.