A research team has successfully treated a human with personalized gene therapy for the first time. In only seven months, researchers in Philadelphia (USA) developed a therapy using CRISPR/Cas9 gene scissors. They treated a six-month-old boy named KJ who was born with a rare genetic defect.
KJ suffered from a CPS1 deficiency (carbamoyl phosphate synthetase I). This genetic defect results in the absence of a vital enzyme. Without this enzyme, ammonia produced during the breakdown of proteins cannot be excreted from the body. As a result, ammonia accumulates in the blood, which can damage the brain. According to one of the study authors, Rebecca C. Ahrens-Nicklas, more than half of children born with CSP1 deficiency die.
The research team had already developed treatments for such diseases that target the liver. Building on this, they developed a base-editing therapy, a form of CRISPR technology. This made it possible to specifically correct one of the two copies of the defective CPS1 gene in KJ.
The researchers developed the appropriate genetic tool within two months. In the following three months, they tested its efficacy and safety on mice and monkeys. Due to the critical state of KJ's health, the US Food and Drug Administration (FDA) granted approval for the drug in just one week.
In February 2025, KJ received the first, smaller, dose of the drug at the age of six months. Two further, larger, doses followed in March and April. The treatment was effective: KJ is now able to breakdown more proteins with fewer ill effects. Although he will have to be monitored medically for the rest of his life, the researchers are encouraged by the initial results.
Cardiologist and study author Kiran Musunuru is confident that "the promise of gene therapy that we've heard about for decades" is now becoming a reality. "It's going to utterly transform the way we approach medicine."
Read more about CRISPR/Cas therapy in our overview article.
Sources
1. Musunuru K, Grandinette SA, Wang X et al. New England Journal of Medicine. DOI: 10.1056/NEJMoa2504747
2. World's First Patient Treated with Personalized CRISPR Gene Editing Therapy at Children’s Hospital of Philadelphia. https://www.chop.edu/news/worlds-first-patient-treated-personalized-crispr-gene-editing-therapy-childrens-hospital (accessed June 25th, 2025)
Image: Luke Jones / Unsplash
