Promises and Pitfalls of Gene Therapy
Saanvi Mazumdar, Staff Writer
Photo source: ‘Miracle’ baby saved by medical breakthrough goes home
IN MAY 2025, a breakthrough in scientific innovation changed the future of personalized medicine. For the first time ever, a customized CRISPR-based gene-editing therapy was approved for in vivo use in a child. A nearly 10-month-old KJ Muldoon received three doses of this treatment that corrected a mutation hindering his body’s ability to process a specific protein. This gene therapy didn’t take place in a lab dish; instead, it was delivered in vivo, meaning it was inserted directly into his body.
KJ was born with a rare disorder called carbamoyl phosphate synthetase 1 (CPS-1), which caused his body to produce abnormal forms of an essential enzyme. This impaired his ability to process nitrogen-containing compounds produced by his body, leading to unusually high levels of ammonia, a highly toxic substance. Although there is a treatment for this condition, CPS-1 disorder typically requires a liver transplant. In Muldoon’s case, however, he would have had to wait months or even years for a suitable donor. Each day KJ had to wait increased the risk of brain damage that could have been fatal.
Instead of waiting for a liver transplant, the Children’s Hospital of Philadelphia offered a different solution. They suggested trying a technique that had never been performed in vivo before. Using a gene editing technology known as CRISPR, the physicians aimed to locate the mutation responsible for the disorder and correct it by repairing the impaired gene. The treatment was delivered by injecting three doses of lipid nanoparticles—a type of fat molecule—into KJ’s bloodstream. These nanoparticles contained RNA encoding editing tools capable of cutting out the mutation from the DNA and repairing it.
Although the researchers weren’t able to directly take liver samples from KJ due to the risks associated with performing a biopsy on such a young child, the decrease in CPS-1 symptoms indirectly indicated that the treatment was successful. Doctors were able to reduce KJ’s reliance on medication to process proteins and successfully manage his blood ammonia levels.
CRISPR therapy has achieved some success in treating genetic disorders, notably sickle cell disease. However, those treatments were administered to adults and designed to be effective for a broad population with the condition. KJ’s case was revolutionary because, for the first time, gene editing was tailored to a single individual’s genome. While this level of specificity has been tested in many model organisms, it has never been attempted in humans due to ethical concerns. As this case marked a major advancement in genetic medicine, it also reignited debates about whether such treatments remain within the bounds of medicine or cross into the area of “designer babies” and eugenics.
What truly differentiates this case from concerns about genetic enhancement is that, in KJ’s situation, the goal was survival—not improvement. This treatment wasn’t about editing physical traits for aesthetic purposes, such as changing eye colour, hair type, or height. Eugenics, rooted in the desire to engineer a “superior” human, has led to discriminatory policies and marginalization. In contrast, gene editing in this case was used to correct a single mutation responsible for a serious health condition in an infant—one that, if left untreated, could have been fatal. This technique avoided the ethical concerns associated with embryonic gene editing. Instead of questioning whether this crosses ethical boundaries, perhaps we should ask ourselves: can saving a life truly be placed in the same category as pursuing genetic perfection?
It’s important to acknowledge the rigorous steps taken to review the use of CRISPR before it was approved for use on a human. As a recently developed method, it underwent extensive safety testing to ensure the therapy was both effective and precise. It had to pass multiple laboratory and clinical trials before being approved for human testing. Additionally, the doctors presented KJ’s parents with all available treatment options, and after careful evaluation, they chose to pursue gene editing.
These preventative methods are extremely important, as they not only protect patients but also help build public trust, especially during clinical trials. Without proper testing or regulatory criteria, the dangers of such treatments can significantly outweigh the benefits.
Although concerns about CRISPR’s unpredictability were valid in its early years, the technology has advanced significantly since its development in the early 2010s. The risk of off-target effects has been dramatically reduced, and newer methods allow genome editing without compromising the integrity of DNA strands. KJ’s recovery is still being closely monitored. Although his condition has improved significantly, the long-term outcomes remain uncertain.
This case has opened the door to a new era in science. Millions of people live with pain and suffering from incurable disorders, and CRISPR has finally offered them hope. Of course, it will take years for this technology to be widely implemented across various diseases—but this is a crucial first step, one that has set medicine on a promising new path.
