Gene Therapy | 2025 | Personalized CRISPR Medicine
When Kyle Muldoon bought a Jalen Hurts jersey for his newborn son, it was a small, hopeful gesture. A tiny jersey for a tiny person who would grow up, run, and live normally.
Two days later, doctors told him his son might never wear it.
In 2025, scientists built a CRISPR-based drug specifically for one baby — and it worked.
This wasn’t a clinical trial. It was a medicine designed for a single human being.
The First Days
KJ Muldoon was born on August 1, 2024. Within days, something was wrong. He was lethargic, unable to feed properly, and struggling to regulate body temperature.
Blood tests revealed ammonia levels above 1,000 µmol/L. Normal is 9–33.
Why this is dangerous
At high levels, ammonia becomes neurotoxic. It damages the brain and can quickly become fatal.
Genome sequencing revealed the cause: CPS1 deficiency.
What CPS1 Deficiency Means
The human body constantly produces ammonia while breaking down protein. Normally, the liver converts it into urea through the urea cycle.
KJ lacked a working version of the CPS1 enzyme, the very first step in this process.
- No CPS1 → ammonia cannot be processed
- Ammonia builds up in blood
- Severe neurological damage risk
The reality
CPS1 deficiency is extremely rare (~1 in 1.3 million) and often fatal in early life.
The only long-term treatment: liver transplant.
But KJ was only days old.
The Turning Point
Doctors proposed something unprecedented: build a gene-editing therapy specifically for KJ.
The idea
Correct the exact mutation in KJ’s DNA using CRISPR-based base editing.
Normally, drug development takes years. This had to be done in months.
It was completed in six.
How the Drug Worked
The therapy used base editing, a precise form of CRISPR that changes a single DNA letter without cutting the DNA.
- Targeted mutation: Q335X in CPS1 gene
- Converted incorrect base → corrected sequence
- Restored functional enzyme production
Delivery system
Lipid nanoparticles carried the editing machinery into liver cells — similar to mRNA vaccine delivery.
Everything was tested in cells and animal models before KJ received it.
The FDA approved it in one week.
What Happened Next
KJ received his first dose at 6.5 months old.
- Ammonia levels stabilized
- Protein tolerance improved
- Medication dependency reduced
After multiple doses, the results were clear.
The moment
KJ went home. He turned one. He wore his jersey.
Why This Changes Medicine
This therapy will likely never be reused. It was designed specifically for KJ’s mutation.
But the platform can be reused for thousands of rare genetic diseases.
- ~7,000 rare genetic diseases exist
- Most have no treatment
- Traditional drug model is too slow
The shift
Medicine may move from “one drug for millions” to “one drug per patient.”
This is not the end. It is the beginning.
The answer for many rare diseases is no longer “never.” It is “not yet.”
Primary Source:
Musunuru K et al. — Patient-Specific In Vivo Gene Editing to Treat a Rare Genetic Disease (NEJM, 2025)
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