A gene therapy has to be developed for a whole patient population, never for one child
The old claim turned out to be wrong and was rejected by evidence.
TaughtDeveloping a gene-editing therapy takes many years and enormous cost, so it only makes sense for diseases shared by thousands of patients. A treatment designed and manufactured for a single individual's exact mutation is science fiction.
NowIn May 2025 a team at Children's Hospital of Philadelphia treated an infant known as KJ Muldoon, who had a severe CPS1 urea-cycle disorder, with a CRISPR base-editing therapy custom-built for his specific mutation, from diagnosis to dosing in about six months. It was the first personalized in-vivo gene-editing medicine made for one person.
What actually happened
KJ was born with a near-total inability to clear ammonia, a condition that kills or brain-damages many affected infants before a transplant is possible. Rather than wait, his doctors and a research team designed a base editor aimed at his exact variant, tested it, manufactured it, and infused it: a timeline measured in months, not the usual years.
The honesty here is important: this is one child, early, and the long-term outcome is not the point being claimed. What was disproved is the categorical belief that bespoke, single-patient gene editing is impractical by nature. The published report in the New England Journal of Medicine and the platform described by the team frame it as a template: the same scaffold, retargeted, for the next rare mutation. The economics and regulation are unsolved. The proof of principle is not.
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Who was taught this
Still standard through 2025, so anyone who finished school between 1950 and 2025 learned the earlier version.