• Posted May 16, 2025

Custom Gene Editing Helps Baby With Rare Condition

FRIDAY, May 16, 2025 (HealthDay News) — A baby born with a rare and deadly genetic disease is the world's first known patient to receive an experimental gene editing treatment designed just for him.

KJ Muldoon from Clifton Heights, Pa., is thriving after the therapy to fix a tiny but essential flaw in his genetic code, doctors said this week. He was diagnosed shortly after birth with severe CPS1 deficiency, The Associated Press reported. 

The condition, estimated to affect about one baby in a million, prevents the body from removing toxic ammonia.

Without treatment, it can be deadly — half of affected infants don’t survive.

Doctors offered KJ’s parents two options: a liver transplant or a first-of-its-kind gene editing therapy.

“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,” KJ's mother, Nicole Muldoon, told AP.

“We prayed, we talked to people, we gathered information, and we eventually decided that this was the way we were going to go,” her husband, Kyle Muldoon, added.

Within six months, scientists from Children’s Hospital of Philadelphia (CHOP), Penn Medicine and other partners created a therapy that targeted KJ’s specific genetic mutation. The case is described in a study published May 15 in The New England Journal of Medicine.

They used a special type of CRISPR, a tool that edits genes and won its investors a Nobel prize in 2020. 

Instead of cutting the DNA, this method — known as base editing — swaps the faulty part for the correct version. Experts say this approach lowers the chance of unwanted changes.

KJ got his first infusion in February. It was delivered via fatty particles designed to carry the treatment into his liver cells, AP reported. 

He has since received two more doses and at 9-1/2 months of age, is now eating more, getting sick less often and taking fewer medications.

"Any time we see even the smallest milestone that he’s meeting — like a little wave or rolling over — that’s a big moment for us,” his mother said.

While it’s still early, doctors are hopeful. But they'll need to monitor KJ for years to come.

“We’re still very much in the early stages of understanding what this medication may have done for KJ,” study author Dr. Rebecca Ahrens-Nicklas, a gene therapy expert at CHOP, said. “But every day, he’s showing us signs that he’s growing and thriving.”

Experts say this case could help pave the way for similar treatments for other rare conditions. Most gene therapies are made for more common diseases because they are expensive to develop. 

But this research, partly funded by the National Institutes of Health, shows that custom therapies may not be as costly as expected, AP said.

Dr. Kiran Musunuru, a gene editing expert at the University of Pennsylvania, said this treatment’s cost was “not far off” from the $800,000 price tag of a liver transplant.

“As we get better and better at making these therapies and shorten the time frame even more, economies of scale will kick in and I would expect the costs to come down,” he added.

“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 said.

More information

The American Society of Gene & Cell Therapy has more on gene editing.

SOURCE: The Associated Press, May 15, 2025