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 worked together to test a CRISPR base-editing therapy the hospital developed, fast-tracking approval of the new therapy by the Food and Drug Administration.
Scientists expedited safety testing using cell cultures and computer programs for fast analysis in order to be able to treat KJ quickly.
KJ received the bespoke CRISPR treatment 6.5 months after birth, receiving three infusions of the therapy as of April 2025. Those delivered the gene-editing treatment, wrapped in fatty lipid molecules to protect it on its way to the liver.
The therapy targets the exact DNA mutation that needs to be changed, instructing cells to produce an enzyme that edits the gene.
It will take long-term monitoring to determine how successful the treatment was, but doctors have already reduced the amount of medication he needs to prevent ammonia buildup.
KJ’s parents also report other signs of improvement, including his ability to eat more protein and reach milestones like waving, rolling over and sitting up by himself, all things they feared he would never be able to do.
CRISPR shows promise for curing rare diseases that have no cure. KJ’s case is a landmark for researchers, who showed that bespoke therapy can be created and delivered to patients in a short period of time.
If KJ’s treatment shows long-term success, doctors could use the same method in other cases, only altering the instructions regarding what gene needs to be changed.
Doctors hope KJ will be the first of many patients who will receive CRISPR therapy individually tailored to address their genetic disease
