Photo by Hush Naidoo Jade Photography on Unsplash (illustrative)
On 15 May 2025, the Children's Hospital of Philadelphia and Penn Medicine reported that an infant named KJ had become the first known patient treated with a personalized CRISPR-based gene-editing therapy. KJ was born with severe CPS1 deficiency, a rare disorder that stops the body from clearing toxic ammonia.
Key facts
The team designed and made the therapy in about six months, from identifying KJ's exact mutation to the first infusion.
KJ received his first dose in February 2025, at six to seven months old, followed by doses in March and April 2025.
The base editor was delivered to his liver in lipid nanoparticles; no serious side effects were reported.
After treatment he could eat more protein and needed less medicine to control ammonia, and the case was published in the New England Journal of Medicine.
Why it matters
Severe CPS1 deficiency can cause brain damage or death in infancy, and children often need a liver transplant to survive. Showing that a gene-editing drug can be built for a single patient in months opens a path for thousands of rare diseases that are too uncommon for traditional drug development.
Worth noting
This is one patient, and doctors say he needs longer follow-up and lifelong monitoring; it is not described as a cure. The team plans a small trial covering several urea-cycle disorders, and the FDA announced a new pathway for individualized treatments in November 2025.