In May 2025, a baby boy named K.J. Muldoon became the first person in history to receive a customized gene editing therapy designed from scratch for his unique genetic mutation. Born with a severe disorder that prevented his liver from processing dietary protein, K.J. would have faced life-threatening ammonia buildup without intervention. Physicians at Children’s Hospital of Philadelphia used a base editor — a technology invented by David Liu’s lab at the Broad Institute in 2016 — to correct the single-letter DNA error. Today, K.J. is thriving.
His case may have been a first, but the team behind it does not want it to be a one-off. Liu receives at least 20 messages a week from desperate parents asking if he can help develop a therapy for their child. The challenge is that each of these children has a different mutation, and traditional drug development models cannot justify the cost of creating a bespoke treatment for a single patient. The New York Times called this dilemma “Too Rare to Care.”
The proposed solution is a new framework Liu calls the “N of 1” therapy model. Instead of designing a clinical trial for each disease, the approach standardizes the platform: use base editing or prime editing to correct the specific DNA misspelling, validate the edit in the patient’s own cells, manufacture the therapy, and deliver it — all within a timeframe that matters for the patient. Prime editing, invented by Liu’s group in 2019, can make any small DNA correction without cutting the DNA double helix, making it safer and more versatile for human therapies.
The goal is ambitious: to treat 1,000 patients with personalized gene editing therapies by 2030. Base editing and prime editing are already being tested in at least 19 clinical trials, with results from seven showing patient benefit. The FDA has granted accelerated approval pathways for some of these therapies, recognizing that the traditional drug development pipeline was never designed for diseases that affect only a handful of people worldwide.
Knowledge takeaway: On-demand gene therapy using base and prime editing is transitioning from a theoretical possibility to a practical framework, with the first patient successfully treated and a roadmap to scale from one patient to a thousand by 2030.