First-ever in vivo CRISPR gene edit saves newborn with fatal CPS1 deficiency

A US research team achieved the first documented in vivo (inside the body) CRISPR gene-editing therapy that rescued a newborn with a rare, life-threatening genetic disorder. The patient, identified as KJ, was diagnosed one week after birth with CPS1 deficiency, a metabolic condition that prevents ammonia removal and occurs in roughly 1 in 1.3 million births. Traditional treatment would be liver transplant, which was not feasible for the infant. Clinicians from Children’s Hospital of Philadelphia, UC Berkeley and the University of Pennsylvania developed a bespoke CRISPR therapy targeting KJ’s specific CPS1 mutation. After six months of rapid development and coordination, doctors administered the tailored treatment beginning 25 February 2025 in a series of infusions. Within two weeks the infant began tolerating protein, completed multiple dosing rounds, and stabilized enough to be discharged home. The team published results in the New England Journal of Medicine and called the case proof that decades of government-funded research can enable personalized in vivo gene therapies. While long-term outcomes (including future need for liver transplant) remain uncertain, investigators say the approach can be scaled and adapted for other patients with genetic diseases. Key figures: Rebecca Ahrens-Nicklas and Kiran Musunuru. Key facts: first in vivo personalized CRISPR therapy applied clinically, disease: CPS1 deficiency (~1/1.3M births), rapid development and multiple dosing in early 2025, published in NEJM.