Barely born, KJ found himself between life and death. Today he smiles, plays, and lives like any other baby. Its overwhelming history marks a world premiere.
A race against the watch to save a baby a few days
Barely a few days after his birth, KJ had to be transferred to the Children’s Hospital in Philadelphia (CHOP). He suffered from a rare metabolic disease, still unknown to his parents, which caused toxic accumulation of ammonia in his blood. Doctors immediately placed the infant under dialysis to stabilize his condition. “”He was very small, but he was stubborn“, Says Nicole, her mother.”It was a fighter from the start“Said his father Kyle.
After intensive first aid, a battery of genetic tests made it possible to identify a Carbamoyl-Phosphate 1 deficiency (CPS1)an extremely rare form of urea cycle disorder. This enzyme normally makes it possible to transform ammonia, naturally produced during the deterioration of proteins, into urea evacuated by the urine. In KJ, this conversion was impossible, causing rapid internal poisoning, especially liver and brain.
Faced with this diagnosis, the perspectives were dramatic. “”When you looked for the disease on Google, two words came back: liver transplant or death. We were in shock“recalls his mother Nicole.”I had bought a jersey for KJ at birth“, says Kyle, inveterate supporter of Philadelphia.”But at that time, chatting with doctors, I told myself that he might never wear it“.
The family then made a painful but vital decision: keeping KJ in the hospital, under constant surveillance, time to find a solution. For weeks, Nicole and Kyle took turns at her bedside, reading, singing, talking to her tirelessly, while continuing to take care of their three other children at Clifton Heights. Their hope? That one day, KJ can go home.
Personalized gene therapy developed in record time
At the time, the only treatment known for this disease was a liver transplant – often risky for such a young baby. But at the CHOP, researcher Rebecca Ahrens-Nicklas has been collaborating since 2023 with Dr. Kiran Musunuru, professor at the University of Pennsylvania and member of the NIH consortium on genomic edition, to explore another track: The creation of tailor -made gene therapies, designed for a single patient.
The team then made a daring bet: directly correct the genetic mutation of KJ thanks to the basic edition, an ultra-precise and personalized form of technology Crispr. In just six months, researchers have designed targeting experimental therapy The specific mutation of the KJ CPS1 geneencapsulated in lipid nanoparticles injected into the liver. Dr. Ahrens-Nicklas explains: “We knew that the method used to deliver the gene machinery to the baby’s liver cells allowed us to give the treatment repeatedly. This meant that we could start with a low dose that we were sure of it was without danger “.
At the end of February 2025, KJ received the first dose. Others will follow in March and April. The treatment, unprecedented in the world, is described in detail in a study published in the New England Journal of Medicine. His cheeks returned to red, I could tolerate a diet richer in protein and experienced a good growing push. But the baby catches a cold and a gastrointestinal disease, and such infections can be very serious for reached babies, with the risk that ammonia can reach dangerous levels for the brain … Dr. Musunuru says: “We were very worried when the baby fell ill, but he simply overcome the disease“. An additional proof that the treatment worked.
A huge hope for other children with rare diseases
Today, KJ has nothing more of the baby that doctors thought of losing. He better digests proteins, hardly takes ammonia drugs, and has overcome several infections without hospitalization. He lives at home, with his brothers and sisters.
“”Since KJ was born, our life revolves around him and his hospitalization. We would have done everything for our children“, Says Nicole.”With KJ, we wanted to understand how to help him live a normal life. When the doctors presented their idea to us, we trusted them, hoping that it could help not only KJ, but also other families in our situation (…) We are so happy to finally be gathered at home, whether with his brothers and sisters … and to be able to breathe“.
For researchers from Chop and Penn, the case of KJ opens a new era. Thousands of rare changes could now be subject to “à la carte” treatments. And although this approach is not yet generalizable, it offers a new chance to children hitherto forgotten with medicine.