Seven-month-old Kyle 'KJ' Muldoon Jr. just became the first person ever treated with a gene therapy designed exclusively for him. And it worked.
KJ was born with a rare genetic disorder that prevented his body from removing toxic ammonia from his blood. Without treatment, the condition causes neurological damage and is often fatal. The options were a liver transplant or experimental gene therapy.
His parents chose the experiment.
Rebecca Ahrens-Nicklas and Kiran Musunuru at the University of Pennsylvania developed a personalized CRISPR base-editing therapy that corrects genetic "misspellings" by altering single DNA bases. Think of it as a molecular spell-checker that fixes one letter instead of deleting entire paragraphs.
After testing in human cells, mice, and primates, they gave KJ his first low dose at seven months old, followed by two higher doses. As of October 2026, he's thriving and hitting all his developmental milestones.
The technology is impressive. The question is whether anyone can afford it.
The treatment cost approximately $1 million—comparable to a liver transplant. Musunuru projects costs will drop "to a few hundred thousand dollars per treatment within the next few years." That's progress, but "a few hundred thousand" is still more than most families will ever see.
Here's what makes this different from existing gene therapies: KJ's treatment was designed exclusively for him and will likely never be used again. Previous CRISPR treatments like those for sickle cell disease were developed for patients with the same genetic variant. This is truly personalized medicine—the cost gets distributed across exactly one patient.
The FDA is creating a new regulatory pathway for ultra-rare genetic variants. The Penn team plans clinical trials with as few as five patients, each with different mutations. If you're thinking "that doesn't sound like a scalable business model," you're right. Which is exactly why this matters.
Base editing works. It saved a baby's life. But the economics look like bespoke tailoring in an era of fast fashion. The question isn't whether we can do this—we just did. The question is how we decide who gets access when the treatment costs what most Americans earn in five years.
