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# They Rewrote His DNA. It Worked.
- URL: https://goodnewsdailytv.com/2026-08-25-they-rewrote-his-dna-it-worked/
- Published: 2026-08-25T15:02:24.000Z
- Updated: 2026-08-25T15:02:22.000Z
- Description: Born with a rare disease that gives most families two options, baby KJ Muldoon became the world's first patient to receive a personalized CRISPR gene therapy built just for his exact mutation. A year later, he's walking, talking, and thriving.
- Author: Good News Daily
- Tags: Scientific Breakthroughs

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When Nicole and Kyle Muldoon searched their newborn son's diagnosis, here's what they found: a liver transplant, or something far worse. Instead, a team of scientists offered them a third option — one that had never been tried in a human being before.

Nobody knew if it would even work. The medicine didn't exist yet. It would have to be built from scratch, for one six-month-old baby, before his body ran out of time.

KJ Muldoon was born with a condition called CPS1 deficiency — a rare defect that stops the liver from clearing ammonia out of the blood. Search it, and the outlook is stark: severe brain damage, or death, unless a transplant arrives in time. For most families hearing that diagnosis, the options end there. But physician-scientists at Children's Hospital of Philadelphia and Penn Medicine had spent years developing something different — a CRISPR-based gene editor designed not for a disease in general, but for one child's exact mutation. KJ became the test of whether that idea could move fast enough to matter.

Doctors Rebecca Ahrens-Nicklas and Kiran Musunuru led a team that worked around the clock with the National Institutes of Health, racing to design, manufacture, and test a therapy built around KJ's own DNA. From diagnosis to first treatment took just six months — far faster than usual. On February 25th, 2025, KJ received his first infusion. Two more followed by that April. Then came the real test: could his body finally handle more dietary protein without his ammonia spiking, the way it always had before?

"What we saw in the first ten days, we really could give him a lot more protein," Dr. Ahrens-Nicklas said. Ordinarily, that extra protein would send ammonia climbing. "They didn't go up," said Dr. Musunuru. KJ tolerated all three infusions with no serious side effects. His team calls it a blueprint — personalized medicine built for an audience of exactly one patient.

A year later, KJ is thriving. He's crawling, walking, climbing over his siblings, and throwing a ball halfway across the room. His diet now includes protein that would once have been dangerous, and he needs less medication to manage it. His case was published in the New England Journal of Medicine, and Nature named him among the people who helped shape medicine that year — not bad, for someone still in diapers.

Doctors are careful to say this isn't a cure. But it's proof that a therapy can be designed for one patient's exact mutation, built, and delivered before a rare disease runs out the clock — and that changes what's possible for every family who's been told there's nothing left to try. The Muldoons have since shared KJ's story with researchers and lawmakers, hoping the next family won't have to wait for a miracle to be invented in time.

"Watching KJ grow and thrive is nothing short of a miracle," Nicole Muldoon says. "We want every child and family facing a rare condition to have that same chance."

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**Sources:** [chop.edu](https://www.chop.edu/news/childrens-hospital-philadelphia-marks-one-year-anniversary-worlds-first-personalized-crispr?ref=goodnewsdailytv.com) · [delco.today](https://delco.today/2026/03/kj-gene-therapy-chop-penn-medicine/?ref=goodnewsdailytv.com)

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