In February, the US Food and Drug Administration (FDA) proposed a radical rethink of how scientists, physicians and manufacturers develop personalized genetic therapies. The regulator’s suggested introduction of a ‘plausible mechanism pathway’ should increase incentives for drug companies to develop personalized treatments, including gene-editing therapies for rare disorders (see go.nature.com/4mnmgzq ). The baby whose life was saved by the first personalized CRISPR therapy Some 350 million people worldwide live with one of more than 5,000 genetic diseases 1 . Many of these conditions could, in theory, be treated with personalized therapies, which correct a single genetic mutation in a person’s DNA using the CRISPR gene-editing tool. In February 2025, KJ Muldoon, a baby born in the United States with a life-threatening metabolic disorder , became the first person to receive this type of personalized treatment 2 . Yet, so far, the bespoke nature of such therapies has posed a huge obstacle to their spread.…