A CRISPR treatment seems to have been effective for a baby’s devastating disease, but it is not clear whether such bespoke therapies can be widely applied

The condition, estimated to affect about one baby in a million, prevents the body from removing toxic ammonia. Without treatment, it can be deadly — half of affected infants don’t survive. Doctors offered KJ’s parents two options: a liver transplant or a first-of-its-kind gene editing therapy.

We’re still very much in the early stages,” a gene therapy expert said. “But every day, he’s showing us signs that he’s growing and thriving.”