A fatal reaction: A cutting-edge gene-editing trial in China went disastrously wrong. A family wants accountability

The young girl tugged on her mother’s hand as they pressed through the doors of the hospital in Shanghai. She was 6 years old, bouncing along in a pink jacket and blue pants decorated with cartoon bears. Behind them, her father rolled a large suitcase with everything the child needed for the weeklong stay: stuffed animals, Play-Doh, an iPad loaded with episodes of Peppa Pig.

She told her parents it felt like they were going on vacation. In fact, they brought her here for an experimental gene therapy. The girl was slipping behind her peers in kindergarten. She still spoke in simple sentences and ate with training chopsticks. Underneath it all was a single mutated DNA base, a T that should have been a C.

“Your ‘book’ has a small mistake, which has caused you to have a disease that affects your growth,” read the children’s version of the informed consent form from the hospital. “Over time, it can get more serious.” Doctors hoped to repair that mistake while her brain was still building itself. It would be a...