A baby known as KJ is the first person in the world to receive a customized CRISPR therapy designed to fix a specific mutation.

PHILADELPHIA, PA - Doctors used personal gene therapy to treat an infant with a deadly genetic disease in a medical first. KJ Muldoon was born in August 2024, and DNA sequencing revealed he had inherited two gene mutations that prevented him from breaking down proteins in food. That leads to a buildup of ammonia that destroys the liver and can cause neurological damage with lifelong consequences. His condition, known as CPS1 deficiency, is one of a group of metabolic diseases with no cure. Half of all babies born with the condition die in their first week of life. Patients who survive are usually treated with drugs to reduce the ammonia in their bodies, but that is usually only partially effective. Babies born with CPS1 deficiency can receive liver transplants, but not until they are a year old, long enough that many have already suffered irreversible brain damage. Getting treatment to KJ quickly was critical for doctors. Researchers at the University of California, Berkeley and the Children’s Hospital of Philadelphia…