At a gene therapy conference, there was excitement about the first correction of a genetic misspelling, along with questions about Sarepta and Editas data.

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.

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