Simple explanation
An infant, KJ Muldoon, was born with a severe metabolic disorder in which the liver cannot process ammonia, a condition that is often fatal early in life. A team designed a base editor aimed at his specific mutation, made it, obtained approval to use it, and gave it to him at seven and eight months old. He improved and went home. One patient — but a demonstration that a medicine can be built for one person.
Go deeper
A patient-specific adenine base editor delivered by lipid nanoparticle was designed against an individual CPS1 variant causing severe carbamoyl phosphate synthetase 1 deficiency, progressing from diagnosis to dosing in approximately six months. Two doses were administered at seven and eight months of age. The case was published in the New England Journal of Medicine and the patient was discharged from Children's Hospital of Philadelphia approximately two months after the second infusion.
Why one patient matters here
Ordinarily a single case proves very little. What this case demonstrates is not efficacy but feasibility: that the design, manufacture, regulatory review and administration of a bespoke editing medicine can be compressed into months rather than years. If that becomes routine, it changes what is possible for the thousands of ultra-rare genetic conditions that will never have a commercial programme.
The FDA has since moved in this direction, publishing draft guidance in February 2026 on how individualised therapies for ultra-rare diseases might be approved — including a framework under which improvement in a single participant could support approval in defined circumstances.
Sources
- New England Journal of Medicine (Musunuru et al.) · 2025
Patient-specific in vivo gene editing to treat a rare genetic disease ↗ - Inside Precision Medicine · 2025
First personalized CRISPR gene editing therapy patient baby KJ discharged ↗