Baby KJ becomes first patient to receive custom gene-editing treatment, offering new hope for rare genetic diseases

Baby KJ becomes first patient to receive custom gene-editing treatment (Image for representation)

In a medical first, a 9½-month-old baby named KJ has become the first person to receive a custom-made gene-editing treatment designed specifically to fix his rare genetic mutation. Diagnosed at just a week old with CPS1 deficiency—a deadly disorder that affects only 1 in 1.3 million babies—KJ’s survival was uncertain. Half of all children born with the disorder die within their first week of life. Those who survive often suffer from severe neurological damage and require a liver transplant.

Refusing to give up, his parents, Kyle and Nicole Muldoon, chose to pursue treatment. That decision led to a historic collaboration between academic researchers, biotech companies, and federal regulators. Their work resulted in a personalised CRISPR-based gene-editing therapy created in record time, and it may signal a new frontier in treating rare diseases, the New York Times reported.

A race against time with unprecedented collaboration

The effort began with an email in August 2023 from KJ’s doctors at the Children’s Hospital of Philadelphia to Dr. Kiran Musunuru, a gene-editing expert at the University of Pennsylvania. In a field where developing and testing therapies can take a decade or longer, researchers had just months to design a treatment to correct the baby’s mutation—an incorrect DNA letter that disrupts his ability to eliminate ammonia, a deadly byproduct of protein metabolism.

The therapy, built on decades of federally funded research, used base editing technology to correct the genetic error. Wrapped in protective lipid particles, the treatment was designed to travel to KJ’s liver, target the faulty gene, and repair it with pinpoint precision using a modified version of CRISPR.

To ensure safety and accuracy, Dr. Musunuru collaborated with Dr. Fyodor Urnov at UC Berkeley and a coalition of companies under the Danaher Corporation, which produced the treatment-grade compound. The FDA fast-tracked approvals, and all companies involved agreed to charge only for raw materials. More than 50 researchers worked around the clock, driven by the urgency of KJ’s condition.

Treatment results and a glimpse of the future

KJ received his first low-dose infusion in February. He slept through the two-hour procedure. In the following weeks, he began tolerating more protein, an early sign of success. Over the next two months, he received two more doses. He no longer experiences the dangerous ammonia spikes that once threatened his life. His medication dosage has been halved, and doctors are now preparing to discharge him home.

The success of KJ’s treatment suggests that personalized gene-editing therapies could become viable for ultra-rare conditions. “Only the CRISPR instructions would need to change for other patients,” said Dr. Peter Marks, former head of gene therapy regulation at the FDA. Costs could be reduced by “an order of magnitude at least.”

A triumph of public investment

Researchers emphasised that this achievement would not have been possible without decades of US government support—from the Human Genome Project to CRISPR’s discovery. “I don’t think this could have happened in any country other than the US,” Dr. Urnov said.

While it's still uncertain if KJ will eventually need a liver transplant, his story marks a turning point in genetic medicine. “This is the most significant thing we have ever done,” said Dr. Urnov. For KJ, and potentially millions of others with rare genetic diseases, the future may now look a little brighter.