New Discoveries: Body, Health & Planet

How one baby’s personalized gene-editing therapy may help reshape treatment for rare genetic diseases Most medicines are developed for thousands or millions of people. But what if a treatment could be created for one child designed around the exact genetic change causing that child’s illness? ​ That possibility became real when physicians and researchers at Children’s Hospital of Philadelphia and the University of Pennsylvania developed a personalized gene-editing treatment for an infant named KJ Muldoon. KJ was born with a life-threatening condition called carbamoyl phosphate synthetase 1 deficiency, or CPS1 deficiency. In 2025, he became the first person to receive a gene-editing medicine designed specifically for his individual genetic variant. In 2026, researchers began working to turn what was learned from his treatment into a broader platform that could potentially help people with several related genetic conditions. ​ Why KJ’s Body Could Not Safely Process Protein ​ When the body breaks down protein, it produces ammonia. Ammonia is toxic, especially to the brain, so the liver normally changes it into urea, which can then leave the body through urine. This process is called the urea cycle. Because of a change in his CPS1 gene, KJ’s liver could not complete the first step of that cycle properly. Ammonia began accumulating in his blood shortly after birth, and he required dialysis when he was only days old. Without careful treatment, high ammonia levels can cause brain injury, developmental difficulties, coma, or death. A Treatment Created Around One Genetic Change Researchers studied KJ’s particular genetic variant and developed a customized form of CRISPR called base editing. Traditional CRISPR methods often cut both strands of DNA. Base editing works more like a highly precise spelling correction: it can change one DNA letter without making a complete double-strand break. The editing instructions were packaged inside tiny fat-like particles called lipid nanoparticles. These particles carried the treatment through the bloodstream to KJ’s liver, where the CPS1 gene needed to be corrected. KJ received three infusions beginning in February 2025. The initial medical report found that he was subsequently able to tolerate more dietary protein and reduce his ammonia-lowering medication to half of its original dose. No serious adverse events were reported during the initial observation period, including periods when he experienced viral illnesses. New England Journal of Medicine study summary At a National Institutes of Health event in 2026, KJ’s mother reported that he was eating more protein, meeting developmental milestones, and experiencing a growth spurt. NIH Rare Disease Day 2026 report The Larger Discovery: A Treatment Platform KJ’s treatment was created for one child, but the larger goal is to develop a reliable treatment platform that can be adjusted for different genetic variants. ​ In 2026, researchers reported early laboratory evidence for a customizable prime-editing platform aimed at seven different urea-cycle disorders and other genetic conditions centered in the liver. Prime editing is related to base editing but can make a wider range of precise DNA corrections. The technology remains experimental, but the platform approach could allow researchers to retain much of the same delivery and manufacturing system while changing the genetic instructions for different patients or conditions. 2026 research published in the American Journal of Human Genetics The U.S. Food and Drug Administration also released draft guidance in February 2026 describing how individualized genetic therapies might be evaluated when a condition affects so few people that a conventional large clinical trial is not possible. The guidance still requires evidence of safety, biological activity, clinical improvement, and manufacturing quality. It is a proposed framework—not automatic approval of these treatments. FDA draft guidance Why This Could Matter Beyond Rare Disease ​ KJ’s story demonstrates how several areas of the body and health are inseparable: A change in one gene altered an enzyme produced by the liver. The missing enzyme affected how the body processed protein. Protein metabolism caused ammonia to accumulate. Ammonia threatened the brain and childhood development. Correcting some liver cells helped the body manage food and waste more effectively. It also shows why research into rare conditions can benefit much larger areas of medicine. The delivery systems, safety testing, genetic tools, and regulatory pathways developed for one disorder may eventually contribute to treatments for other inherited metabolic, neurological, cardiovascular, immune, or childhood conditions. Important Questions Remain. ​ This treatment should not yet be described as a cure. It was created for one child, and researchers do not yet know how long its benefits will last or whether additional treatment or a liver transplant may eventually be needed. Gene editing can also carry risks, including unintended genetic changes, immune responses, inflammation, liver effects, and consequences that may not become visible for years. KJ will require long-term medical monitoring. Cost and access are also major concerns. A scientific method that works for one patient must still become safe, reproducible, and financially accessible before it can help families more widely.