Baby Receives First Personalized CRISPR Gene Therapy and Is Thriving

Medical Breakthrough Changes Everything

A six-month-old baby named KJ has become the first person in medical history to receive a completely personalized CRISPR gene therapy, marking a revolutionary moment in precision medicine. The infant was successfully treated with a customized CRISPR gene editing therapy by a team at Children's Hospital of Philadelphia (CHOP) and Penn Medicine, making this the first known case of a personalized CRISPR-based medicine administered to a single patient. The treatment was administered safely, and he is now growing well and thriving.

KJ was born with a rare metabolic disease known as severe carbamoyl phosphate synthetase 1 (CPS1) deficiency. CPS1 deficiency prevents the liver from fully breaking down protein byproducts, causing toxic levels of ammonia accumulation. High levels of ammonia can cause coma, brain swelling and may be fatal or cause permanent brain damage. Unable to convert ammonia to urea, newborn KJ was in serious risk of brain or liver damage, and had to be kept on medications and an extremely restrictive diet to avoid protein metabolism.

Racing Against Time

After years of preclinical research with similar disease-causing variants, Ahrens-Nicklas and Musunuru targeted KJ's specific variant of CPS1, identified soon after his birth. Within six months, their team designed and manufactured a base editing therapy delivered via lipid nanoparticles to the liver in order to correct KJ's faulty enzyme. The speed was crucial since babies with this condition face constant danger while waiting for traditional treatments like liver transplants.

In late February 2025, KJ received his first infusion of this experimental therapy, and since then, he has received follow-up doses in March and April 2025. The researchers were cautious about safety, starting with low doses. "We were very concerned when the baby got sick, but the baby just shrugged the illness off," said Penn geneticist Kiran Musunuru.

Revolutionary Technology Platform

CRISPR (clustered regularly interspaced short palindromic repeats)-based gene editing can precisely correct disease-causing variants in the human genome. What makes this case extraordinary is that previous CRISPR therapies have only targeted common diseases affecting thousands of patients. So far, the only FDA-approved and standardized CRISPR therapies target two diseases found in tens of thousands of patients. CRISPR is an incredibly complex tool and expensive to wield, leaving its magic beyond the reach of millions of children and adults worldwide who collectively suffer from extremely rare genetic disorders.

The multi-institutional group collaborated to design, test, manufacture, and coordinate regulatory review by the US Food and Drug Administration (FDA), so that the therapy could be delivered as quickly as possible. This collaboration demonstrates how academic institutions, biotech companies, and regulatory agencies can work together to save lives when time is critical.

Hope for Rare Disease Patients Everywhere

Since K. J. received the first dose of his customized therapy in February, he has been able to eat more protein and has needed less ammonia-lowering medication. Although K. J. remains under observation at the Children's Hospital of Philadelphia, he's growing well and can roll over and wave, his parents said at the press briefing.

Years and years of progress in gene editing and collaboration between researchers and clinicians made this moment possible, and while KJ is just one patient, we hope he is the first of many to benefit from a methodology that can be scaled to fit an individual patient's needs," said Rebecca Ahrens-Nicklas, director of the Gene Therapy for Inherited Metabolic Disorders Frontier Program at CHOP. "I don't think I'm exaggerating when I say that this is the future of medicine," said Kiran Musunuru. "My hope is that someday no rare disease patient will die prematurely from misspellings in their genes, because we'll be able to correct them."