In February 2025, doctors at Children’s Hospital of Philadelphia did something that had never been done before in the history of medicine. They took a six-month-old baby named KJ, who was born with a fatal genetic disease called CPS1 deficiency, and gave him a drug designed for one person on the entire planet. Him.
What Is CRISPR?
CRISPR stands for Clustered Regularly Interspaced Short Palindromic Repeats. It’s a molecular tool that scientists borrowed from bacteria, which have been using this system for billions of years as a defense mechanism against viruses. In 2012, Jennifer Doudna and Emmanuelle Charpentier figured out how to reprogram this bacterial immune system to edit any DNA sequence — earning them the Nobel Prize in 2020.
Think of your DNA as a massive book, three billion letters long. Sometimes there’s a typo — a single wrong letter in the wrong place. CRISPR is like a molecular spell checker that can find that exact typo and fix it.
Three Breakthroughs That Changed Everything
1. The First Personalized Gene Therapy (Baby KJ)
Baby KJ was born with CPS1 deficiency — his body couldn’t process ammonia, a toxic byproduct of protein metabolism. Without treatment, ammonia would build up and cause brain damage or death. He was too young and too small for a liver transplant.
Researchers at Penn and CHOP sequenced KJ’s DNA, identified the exact mutation causing his disease, and built a custom CRISPR editor targeting his specific genetic typo. They packaged it in lipid nanoparticles and injected it. Within days, his ammonia levels stabilized. He went home.
A custom drug, for one patient, designed and manufactured in months.
2. Epigenetic Editing — No Cutting Required
Traditional CRISPR works by cutting DNA, which carries risks of unintended damage. A new approach called epigenetic editing doesn’t cut anything. Instead, it adds or removes tiny chemical tags (methyl groups) that control whether genes are turned on or off.
Think of it as the difference between cutting a page out of a book versus putting a sticky note over a paragraph. The text is still there, but the cell can’t read it. This is reversible, more precise, and potentially safer for conditions where you want to silence a gene rather than destroy it.
3. One Shot That Permanently Lowers Cholesterol
In November 2025, Verve Therapeutics published results of a clinical trial where a single CRISPR injection permanently lowered LDL cholesterol by editing the ANGPTL3 gene in liver cells. One shot. Not a daily pill. Not a monthly injection. One treatment, permanent effect.
The implications go beyond cholesterol — the same approach could target Lp(a) (a genetic risk factor for heart attacks that affects 1 in 5 people) and potentially even blood pressure.
Why This Matters
There are over 7,000 known rare genetic diseases. Most have no treatment. CRISPR is turning “untreatable” into “curable” — and the technology is getting faster, cheaper, and more precise every year.
The first approved CRISPR therapy (Casgevy for sickle cell disease) arrived in 2023. Baby KJ’s personalized cure came in 2025. Epigenetic editing and one-shot cardiovascular treatments are in clinical trials now. We’re watching medicine transform in real time.
Watch the Full Episode
We go much deeper into the science, the delivery problem being solved by nanoparticles, and what Jennifer Doudna herself says about CRISPR’s future. Watch on YouTube or listen on Spotify.