An American baby, KJ Muldoon, born with a rare and life-threatening genetic disease, is growing normally after undergoing the first successful personalized gene therapy.
In a new study, researchers report that the baby is among the first humans to receive this therapy to correct tiny yet critical errors in his genetic code. These errors are fatal to half of the affected infants. Although this treatment is not anticipated to become mainstream, doctors hope the technology will eventually aid millions with similar conditions.
Dr. Kiran Musunuru from the University of Pennsylvania said, “This is the first step towards the use of gene editing therapies to treat a wide variety of rare genetic disorders for which there are currently no definitive medical treatments.” Musunuru co-authored the study, examining the baby’s treatment.
Experts claim that there are close to 350 million people around the world who suffer from rare diseases, much like the one the baby from Pennsylvania suffered from. Most of these diseases are genetic.
The case of the US baby is quite particular, as he was born with severe CPS1 deficiency. According to experts, this disease is estimated to affect one in a million babies. Infants who suffer from this condition usually lack an enzyme needed to help remove ammonia from their bodies. Others with the condition may require liver transplants.
This baby is called KJ.
He was born with a rare genetic disorder called CPS1 deficiency, which affects about one in 1.3 million babies and can be fatal.
Doctors informed his parents that he was dying.
But in a groundbreaking medical first, KJ Muldoon was treated with a… pic.twitter.com/urbiLTUqfz
— Massimo (@Rainmaker1973) May 16, 2025
After learning of the odds KJ was facing, his parents, Kyle and Nicole, decided to undergo the experimental procedure due to their fear of losing their baby.
Before deciding to undertake the treatment, KJ’s parents weighed all of their options. Nicole explained to NBC News, “We were, like, you know, weighing all the options, asking all the questions for either the liver transplant, which is invasive, or something that’s never been done before.”
On the other hand, Kyle said, “We prayed, we talked to people, we gathered information, and we eventually decided that this was the way we were going to go.”
BABY GETS CUSTOM DNA FIX — AND IT’S WORKING
Doctors just edited a baby’s DNA — and no, this isn’t sci-fi.
They used CRISPR, a tool that lets scientists literally rewrite your genetic code like it’s a Google Doc.
KJ Muldoon was born with a deadly disorder and no cure. So… https://t.co/3YeNbSCud4 pic.twitter.com/LOPLiskPuE
— Mario Nawfal (@MarioNawfal) May 15, 2025
It took just six months for researchers at Children’s Hospital of Philadelphia and Penn Medicine, alongside their partners, to create the personalized gene therapy to treat KJ’s faulty gene. Researchers used CRISPR, a gene editing tool that won its inventors the Nobel Prize in 2020.
In February 2025, KJ received his first IV fusion with the gene editing therapy. It was delivered through fatty droplets called lipid nanoparticles, which are taken up by cells in the liver. After receiving two more fusions in March and April, KJ is now developing positively.
