Baby KJ’s father returns to CHOP as a construction worker, building its new patient tower
Kyle Muldoon joined the project in December 2024 while his son's life-threatening genetic condition was being treated at CHOP, where he received a first-of-its-kind gene editing therapy.
Inside a heated tent on the Children’s Hospital of Philadelphia campus, 17-month-old KJ Muldoon wiggled around in his mother’s arms, smiling and clinging to a multicolored toy.
This time, the toddler who has been called one of the top 10 people who helped shape science in 2025 was not here for a medical appointment.
He was there to celebrate a 26-story patient tower at CHOP that his father, Kyle Muldoon, a longtime construction worker, is helping build. Called Roberts Children’s Health, the new inpatient complex is set to launch in 2028 and significantly expand the number of beds available for patients at CHOP’s main campus.
Kyle Muldoon had joined the project back in December 2024, when KJ was still hospitalized at CHOP, where his life-threatening genetic condition was successfully treated with a first-of-its-kind personalized gene editing therapy.
But in the months before the treatment developed by doctors at CHOP and the Hospital of the University of Pennsylvania sparked international attention, KJ’s father was recently unemployed. The Clifton Heights father of four had accepted a layoff to focus on his sick son.
When he was connected with the person running the $2.6 billion construction project at CHOP, he asked for a job and explained he would “essentially be living next door.”
Muldoon joined the crew in December 2024, allowing him to stay close by during KJ’s 307-day-long stay and contribute to a project that feels meaningful to him.
“Every day when I get up, I know what I’m doing this for,” Muldoon said.
His son KJ was born in August 2024 with a metabolic disorder that puts babies at risk of severe brain damage and is fatal in half of cases. Called severe carbamoyl phosphate synthetase 1 (CPS1) deficiency, it prevented KJ’s liver from being able to process protein.
Doctors Kiran Musunuru and Rebecca Ahrens-Nicklas used a gene-editing technology known as CRISPR to create a personalized drug that would fix the genetic mutation that was driving KJ’s disease. After receiving three doses, he was able to go home last June.
“This pipe dream that sounded like it came from a sci-fi movie became a reality,” Muldoon said.
The medication is not a cure, but it has dramatically improved KJ’s liver function and made the effects of his disease milder.
The treatment approach has been hailed for its potential for rare-disease drug development. The U.S. Food and Drug Administration in the fall announced a new approach to clinical trials to test novel drugs like the one designed for KJ, who was called “a trailblazing baby” by the British scientific journal Nature when it named him to its year-end top 10 influential people list.
With dietary restrictions and daily medication to keep his ammonia levels down, the toddler has been able to meet milestones, like walking and saying some words (currently a lot of “mama” and “dada”).
These days, KJ likes playing catch, eating, and chasing around his siblings.
“Sometimes you got to sit back and take it all in, because we never knew if that was going to be a possibility,” Muldoon said.
The new tower’s construction is funded in part by a $125 million donation from Comcast CEO Brian Roberts and his wife Aileen, whose name will be on the new building.
Wednesday’s event included signing and raising the final structural beam of the building’s frame.
On the beam were colorful messages from patients at CHOP who were asked to write down their dreams.
Brian Roberts read some of their notes at the event. One girl said she wanted to become a nurse anesthetist so she “can help people and own a porch.” Another said, “My wish is that every kid that goes to Roberts Children’s Health comes out better and stronger.”