A baby born with a life-threatening genetic disorder is now showing signs of health and development after receiving a groundbreaking, personalized gene editing treatment. The case is offering hope to the millions of people worldwide affected by rare diseases that currently have no cure.
Little KJ Muldoon, born in Pennsylvania, was diagnosed shortly after birth with a severe genetic condition known as CPS1 deficiency. This disorder, believed to affect about one in a million infants, prevents the body from eliminating ammonia — a waste product that can become toxic if it accumulates. Most babies with this condition face devastating outcomes, including early death, unless treated with invasive procedures like liver transplants.
KJ’s parents, Kyle and Nicole Muldoon, were confronted with an unimaginable decision. They could pursue a liver transplant or try an experimental gene editing therapy — something that had never been done for this condition. After thorough consultation and consideration, they chose the experimental route.
A Custom Solution Using Base Editing Technology
A team of scientists and clinicians from the Children’s Hospital of Philadelphia and Penn Medicine collaborated to develop a customized therapy for KJ using a next-generation gene editing technique known as base editing. This method allows scientists to precisely correct a single “letter” in the DNA sequence without cutting the strand — a key advancement over earlier CRISPR tools, which carried more risk of off-target effects.
In just six months, the team created a treatment that used lipid nanoparticles — tiny fat-like particles — to deliver the corrected genetic instructions directly to liver cells through an IV infusion. KJ received the first dose in February and two follow-up treatments in March and April. Throughout the process, he showed no signs of discomfort, even sleeping during his first infusion.
Signs of Progress Offer New Hope
Since receiving the therapy, KJ has made significant progress. He is eating better, recovering more easily from common illnesses, and requires fewer medications. For a condition that usually proves fatal early on, these small milestones — like waving or rolling over — mean everything to his family.
Doctors emphasize that the treatment is still in its early stages and long-term monitoring is crucial. However, initial results are promising, and researchers are cautiously optimistic.
A New Era for Rare Disease Treatments
This case marks one of the first successful uses of a gene editing therapy tailored to a single patient. Experts believe this could pave the way for similar approaches to treating other ultra-rare conditions. While most gene therapies target more common disorders due to financial viability, this case suggests that personalized treatments may not be as cost-prohibitive as once feared.
The cost of developing KJ’s therapy was comparable to a liver transplant — roughly $800,000. With time, researchers hope that production processes will become more efficient, ultimately driving down costs.
The implications go beyond KJ. Scientists hope that the knowledge gained from this project will accelerate development for other rare diseases, bringing lifesaving treatments to patients who’ve historically had limited options.
As one neurologist noted, breakthroughs like this tend to trigger a domino effect in science. Once a path is proven, other teams can build on it, moving faster toward solutions.
While many hurdles remain, the success of KJ’s treatment is a powerful reminder of how innovation and persistence can rewrite futures — one life at a time.
