Custom Gene Editing Used to Treat US Baby with Rare Disease

WASHINGTON, United States — A U.S. infant suffering from a rare genetic disorder has become the first person in history to receive a customized gene-editing treatment, offering new hope to others with similarly obscure conditions, doctors announced Thursday.

The young trailblazer is KJ Muldoon, a 9-and-a-half-month-old baby boy known for his round cheeks and bright blue eyes.

Shortly after his birth, KJ was diagnosed with CPS1 deficiency—a rare and serious disorder caused by a mutation in a gene responsible for producing an essential liver enzyme. This condition prevents the body from eliminating certain toxic waste products generated during metabolism.

“You Google ‘CPS1 deficiency’ and it’s either fatality rate or liver transplant,” the baby’s mother, Nicole Muldoon, says in a video released by Children’s Hospital of Philadelphia, where the baby was treated. With the prognosis grim, doctors suggested something that had never been done before: a personalized treatment to fix the baby’s genome using what amounts to a pair of molecular scissors — the technique called Crispr-Cas9, which earned its creators the Nobel prize for chemistry in 2020.

The boy’s father, Kyle Muldoon, recalled the difficult choice he and his wife had to make.

“Our child is sick. The options were either a liver transplant or a medication that had never been tried on anyone before,” he said.

Ultimately, they chose to proceed with the experimental treatment—a customized infusion designed specifically for their son to correct the faulty DNA letters among the billions that make up the human genome.

“The treatment was specifically designed for KJ—his genetic variants are unique to him. This is personalized medicine,” explained Dr. Rebecca Ahrens-Nicklas, a pediatric genetics specialist and member of the medical team.

Once the customized infusion reached his liver, the CRISPR-based molecular scissors entered his cells and began editing the faulty gene.

The team, whose findings were published Thursday in the New England Journal of Medicine, said the outcome offers hope for others with rare genetic disorders.

Since the treatment, KJ has been able to tolerate a protein-rich diet—which was previously restricted by his condition—and requires fewer medications.

However, doctors emphasized the need for long-term monitoring to assess the ongoing safety and effectiveness of the therapy.

Dr. Ahrens-Nicklas expressed optimism that the treatment could eventually allow KJ to live with minimal or even no medication.

“We hope he’s just the first of many who will benefit from a personalized approach that can be adapted to meet each patient’s unique needs,” she said.