Gene-Editing Miracle Saves Infant’s Life, Unprecedented Gateway for Personalized Treatment

In a medical milestone, physicians have employed a personalized gene-editing therapy for the first time as a treatment for a baby boy with a severe and deadly genetic disorder—marking a new era of personalized medicine that could be of benefit to thousands of families with rare diseases.

K.J. Muldoon was two days old when physicians observed that something was wrong. He was extremely sleepy and was struggling with feeding. Soon, tests revealed a dire diagnosis of CPS1 deficiency, a metabolic disorder due to a genetic mutation that interferes with the body’s capacity for removing toxic amounts of ammonia. Unless he received treatment, K.J. would have had to be given a liver transplant in order to stay alive.

But in a stunning twist, his medical team at the Children’s Hospital of Philadelphia designed a personalized CRISPR gene-editing treatment—just for his individual mutation. It was developed and sanctioned in a mere six months, a process that can take years.

The treatment employed lipid nanoparticles to target delivery of the gene-editing agent directly into K.J.’s cells in his liver, fixing the malfunctioning gene and allowing his body to produce the otherwise-lacking enzyme. Since being administered three shots from February through April, K.J. has improved dramatically: he is eating better, weighs more, and needs fewer medications.

“This is the future of medicine,” said Dr. Kiran Musunuru, a Penn Medicine professor treating K.J. He and Dr. Rebecca Ahrens-Nicklas, the director of the hospital’s inherited metabolic disorder program, hope this model of treatment can be replicated in the near future to treat other children with their own, extremely rare, one-of-a-kind genetic conditions. Experts say that this case is a significant breakthrough in the applications of gene-editing for individual treatments. “It’s a very big deal,” said Boston Children’s Hospital’s Dr. Timothy Yu, who is not involved with the case.

Now 9½ months old, K.J. is doing well. Soon, he is due to return home for the first time with his three siblings and his parents. “I felt like he was here for a reason and that he was going to be special,” said his dad, Kyle Muldoon.

This historic report was initially published in The Wall Street Journal. You may read the complete article here: CRISPR Gene-Editing Therapy Saves Infant in Philadelphia (Wall Street Journal, May 16, 2025).