Personalized gene editing helped one baby: can it be rolled out widely?

Late last year, dozens of researchers spanning thousands of miles banded together in a race to save one baby boy’s life. The result was a world first: a cutting-edge gene-editing therapy fashioned for a single person, and produced in a record-breaking six months¹.

Now, baby KJ Muldoon’s doctors are gearing up to do it all over again, at least five times over. And faster.

The ground-breaking clinical trial, described on 31 October in the American Journal of Human Genetics², will deploy an offshoot of the CRISPR–Cas9 gene-editing technique called base editing, which allows scientists to make precise, single-letter changes to DNA sequences. The study is expected to begin next year, after its organizers spent months negotiating with US regulators over ways to simplify the convoluted path a gene-editing therapy normally has to take before it can enter trials.

Developing KJ’s treatment was “a pretty hectic and intense six months”, says Kiran Musunuru, a cardiologist at the Perelman School of Medicine at the University of Pennsylvania in Philadelphia, and one of KJ’s doctors. “But...