For the first time, a CRISPR drug treats a child’s unique mutation

Photograph: Children's Hospital of Philadelphia

May 15th 2025|4 min read

WITHIN DAYS after KJ was born in Philadelphia in August 2024 it was clear that something was wrong. He was not eating and slept too much. Blood tests revealed sky-high levels of ammonia, a toxic substance the body usually expels. Genome sequencing confirmed that he had a rare genetic disease called carbamoyl-phosphate synthetase 1 (CPS1) deficiency, which often kills in infancy, and for which no good neonatal treatment exists. Then one of his doctors suggested something radical: a gene-editing drug designed specifically for him.