In a stunning medical breakthrough that effectively brings designer babies out of the realm of science fiction, a nine-month-old baby named KJ is the first person in the world to receive a genetically customized CRISPR therapy to treat a genetic mutation that, if left untreated, would cause severe and deadly inborn epilepsy. Born with a rare disorder known as severe carbamoyl phosphate synthetase 1 (CPS1) deficiency, of which only 1 in 1.3 million people in the United States are thought to be affected, KJ faced a grim prognosis: half of infants with his condition die within weeks of birth. But thanks to a bespoke gene-editing treatment developed in just six months, he is now thriving, hitting developmental milestones, and rewriting the future of precision medicine.
A Race Against Time: Diagnosing a Devastating Disorder

KJ started displaying worrisome symptoms including ethargy, vomiting, seizures, and irregular breathing 48 hours after birth, all indicators of toxic ammonia buildup in his system. The worst was confirmed by genetic testing: he had inherited two defective copies of the CPS1 gene, which left nitrogen waste unable for processing in his liver. The ammonia would keep attacking his brain without intervention, perhaps causing coma or death.
Doctors bought time while they sought a fix by immediately putting him on dialysis and nitrogen-scavenging medications. Although KJ was too small and delicate for surgery, traditional treatment would have called for a liver transplant. His sole wish is Customized to his precise mutation, a never-before-tried CRISpen treatment.
CRISPR’s Next Evolution: From One-Size-Fits-All to Precision Editing

Approved CRISpen treatments such as those for sickle cell disease—have until now worked by rendering malfunctioning genes inactive. But KJ’s case called for something far more complicated: fixing a unique mutation in a broken gene.
Now introduce base editing, a perfected CRISpen method that alters one DNA letter without altering the genome. Years of preparation for this event had gone toward testing custom gene therapies in animals for urea cycle conditions like CPS1 deficiency. Dr. Kiran Musunuru and Dr. Rebecca Ahrens-Nicklas had spent years getting ready. They proposed an unheard-of experiment: design a therapy specifically for KJ when he was born.
The Six-Month Miracle: Engineering a Cure From Scratch

The team found KJ’s mutation Q335X, a genetic “stop sign” that stopped protein synthesis and developed a molecular fix in a dramatic sprint against biology. They rebuilt the defective DNA code using base editing, enabling his liver to generate the missing enzyme.
Just six months following his birth, by February 2025 KJ underwent his first infusion. Two more doses followed without any major side effects. The outcomes are His protein tolerance rose, his ammonia levels steadied, and most remarkably he started sitting up on his own a mark his parents worried he might never reach.
Beyond Survival: A New Era of Personalized Medicine
“This isn’t just about KJ,” Dr. Ahrens-Nicklas emphasized. “It’s proof that we can design cures for one patient at a time.” While the treatment is still experimental, its implications are staggering:
- Faster development: Traditional gene therapies take years; KJ’s was ready in months.
- Lower risk: By being more exact than standard CRISpen, base editing minimises inadvertent DNA damage.
- Scalability: Similar strategies could address thousands of extremely rare genetic diseases.
Ethical Crossroads: Who Gets Access to a Million-Dollar Cure?
Given individualized CRISpen treatments probably costing millions per patient, difficult questions surface:
- Will insurers cover one-off treatments?
- Can the process be streamlined for broader use?
- Should governments fund lifesaving but exorbitant interventions?
Experts argue that costs will drop as technology advances, but for now, KJ’s case remains a privileged exception.
What’s Next? A Lifetime of Monitoring And Hope
KJ’s journey is not over yet. For years, doctors will keep an eye on his liver function, neurological development, and possible long-term effects. But for his parents, every laugh and wobbly step is a gift from God.
Dr. Musunuru says, “Decades of gene therapy hype just became reality.” And for families dealing with rare diseases, that is nothing short of a revolution.
Final Thought
What other “impossible” cures might be possible in the future if science can change a baby’s DNA in just a few months? KJ’s story could be the first chapter in a new medical playbook that says no disease is too rare to be treated.
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Jan loves Wildlife and Animals and is one of the founders of Animals Around The Globe. He holds an MSc in Finance & Economics and is a passionate PADI Open Water Diver. His favorite animals are Mountain Gorillas, Tigers, and Great White Sharks. He lived in South Africa, Germany, the USA, Ireland, Italy, China, and Australia. Before AATG, Jan worked for Google, Axel Springer, BMW and others.