A trial built around one baby is showing how patient-driven research can go mainstream. For months, the researchers trying to save KJ Muldoon knew him only as ‘Patient Eta’.
He was born in August 2024 with CPS1 deficiency, an ultra‑rare urea‑cycle disorder that can send ammonia levels soaring and devastate the brain. A liver transplant is often the only route forward — if the baby survives long enough.
Baby KJ Muldoon with clinicians Rebecca Ahrens-Nicklas (right) and Kiran Musunuru (left) at the Children’s Hospital of Philadelphia. Photo courtesy of Children’s Hospital of Philadelphia.
Nobel laureate Jennifer Doudna , who co-developed CRISPR–Cas9 technology and co-founded the Innovative Genomics Institute, recalls the turning point for baby KJ: “He was diagnosed in late 2024. They identified the cause, and it was something that could, in principle, be corrected by a CRISPR modality.” At 2 days of age, KJ was transferred to the Children’s Hospital of Philadelphia because of inordinately high levels of ammonia in his blood.
Nature Medicine published a clinical update in Research Highlights on 21 Apr 2026.
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