First Patient in the World Treated with Gene Editing Appears in the United States
According to an AFP report from Washington, a child in the United States with a rare disease has become the world’s first patient to receive personalized CRISPR gene-editing therapy. A medical team from Children’s Hospital of Philadelphia and the University of Pennsylvania successfully applied a customized CRISPR gene-editing therapy to a child (9.5 months old) with a rare genetic disease. The findings were published in the New England Journal of Medicine on May 15, 2025, and presented at the annual meeting of the American Society of Gene & Cell Therapy.
The patient, named KJ Muldoon, was diagnosed shortly after birth with a rare and severe disorder: carbamoyl phosphate synthetase 1 (CPS1) deficiency. This is a rare autosomal recessive disorder that causes hyperammonemia; it results from CPS1 gene mutations that reduce or abolish CPS1 activity, block the urea cycle, impede ammonia metabolism, and produce hyperammonemia leading to encephalopathy and liver disease. Clinical manifestations are varied; onset can occur at any age, but early-onset forms in the neonatal period predominate, with poor prognosis and high disability and mortality rates.
Doctors at Children’s Hospital of Philadelphia proposed using Crispr-Cas9 gene-editing technology—the so-called “molecular scissors”—to custom-repair Muldoon’s genes. The proposal was approved by the parents; the hospital designed a dedicated therapeutic drug and infused it intravenously.
After reaching the liver, the molecular scissors inside the drug entered cells and began editing the defective genes. Early results show Muldoon can now tolerate more protein that was previously strictly restricted, and the required medication dose has dropped markedly. Despite early efficacy, doctors say he will need long-term follow-up to monitor safety and treatment effects.
The Muldoon trial may bring new hope to many patients. CRISPR gene editing was invented by the French biochemist Emmanuelle Charpentier and the American chemist Jennifer A. Doudna, who received the 2020 Nobel Prize in Chemistry for this breakthrough technology.
Doudna also wrote a book, A Crack in Creation: Gene Editing and the Unthinkable Power to Control Evolution, introducing this revolutionary biotechnology. In it, the laureate writes that in laboratory-grown human cells, the new gene-editing technology has already corrected many genetic diseases, including cystic fibrosis, sickle-cell disease, certain forms of blindness, and severe combined immunodeficiency. With CRISPR, scientists can find and correct a single mutation among the 3 billion base pairs of human DNA.
Since this new technology emerged, medicine has hoped it would play a major therapeutic role, but for various reasons human trials were slow to begin. The Children’s Hospital of Philadelphia trial opened the way for CRISPR in human disease treatment; perhaps in future we will see it applied to more conditions.
Cancer is a highly lethal disease caused by gene mutations, and medicine has long hoped gene therapy would work new miracles for cancer patients. But there are as yet no clinical studies of CRISPR for cancer; perhaps before long we will see such reports.