In a first-of-its-kind medical breakthrough, a baby named KJ Muldoon has become the first person on Earth to receive a completely personalized gene-editing treatment, tailored just for him, and it may have saved his life.
Born in the summer of 2024, KJ was diagnosed with a rare and life-threatening condition called Carbamoyl Phosphate Synthetase 1 (CPS1) deficiency. It’s a genetic disorder that makes it almost impossible for the body to get rid of toxic ammonia, and without treatment, about half of the affected infants don’t survive.
Until now, the only way to manage severe CPS1 was with a liver transplant. But KJ’s doctors at the Children’s Hospital of Philadelphia (CHOP) and Penn Medicine offered his family something extraordinary: an experimental CRISPR-based gene therapy, designed just for him.
The procedure worked like this: using CRISPR, a Nobel Prize–winning gene-editing technology, scientists scanned KJ’s 20,000 genes, located the exact mutation causing his disorder, and then corrected it using tiny molecular scissors delivered directly to his liver. This wasn’t a one-size-fits-all treatment. It was a genetic fix custom-built for a single patient: KJ.
So far, KJ has received three doses of the therapy, and the results are promising. According to Penn Medicine, he has shown no serious side effects. More importantly, he’s now smiling, growing, and preparing to celebrate his first birthday in August.
“While KJ will need to be monitored carefully for the rest of his life, our initial findings are quite promising,” said Dr. Rebecca Ahrens-Nicklas, director of the Gene Therapy for Inherited Metabolic Disorders Frontier Program at CHOP.
The science behind this is groundbreaking. CRISPR, which stands for Clustered Regularly Interspaced Short Palindromic Repeats, allows doctors to edit genes with pinpoint precision, cutting out the bad and replacing it with the correct instructions.
“This is mind-blowing and we should all be very, very excited,” said Dr. Brian Brown, Director of the Icahn Genomics Institute in New York City.
KJ’s treatment, now published in the New England Journal of Medicine, opens the door to a future where deadly inherited disorders might be treated before symptoms even begin—not just managed, but potentially cured.
For now, KJ remains under close observation at the hospital—but he’s gaining weight, laughing, and showing the world what the future of medicine might look like. His mother, Nicole Muldoon, summed it up with emotion: “Now, when I get to hold him, and he’s laughing and jumping around, that is…very heartwarming, because I didn’t know if that was going to happen, at one point.”
For more details, refer to this article published in the New England Journal of Medicine.
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