A Medical Breakthrough: How CRISPR Gene Editing Saved Baby KJ*

*features TechTrek writers’ interview with Gina Kolata, the New York Times Reporter on the Baby KJ Case

Link to Podcast Interview with Gina Kolata

By Ananya Chopra and Olivia Allison,

The Lawrenceville School, NJ

In a medical first that could transform the treatment of rare genetic diseases, researchers at the Children’s Hospital of Philadelphia successfully used CRISPR gene editing technology to save an infant born with a severe metabolic disorder. TechTrek writers Ananya Chopra and Olivia Allison interviewed Gina Kolata, the New York Times reporter who met with the researchers and doctors on baby KJ’s case to cover the story. Baby KJ was born with carbamoyl phosphate synthetase 1 (CPS1) deficiency, a rare and devastating genetic disorder that affects the body of one in 1.3 million babies’ ability to process ammonia. Without treatment, half of all babies born with this rare enzymatic deficiency suffer severe brain damage and die within a week, and the other half endure severe developmental and mental setbacks, requiring a liver transplant later in life. As toxic ammonia accumulated in Baby KJ’s body through protein metabolism, doctors limited his protein intake to a miniscule amount, just barely enough to support his physical development. Consequently, he was in the 7th percentile in weight at 6 months old. 

Image of Baby KJ, recipient of the unprecedented personalised gene therapy

The clock was ticking, and researchers needed to act swiftly before irreversible neurological damage occurred. What made this case extraordinary was not just the urgency, but the unprecedented approach taken by the medical team. Baby KJ was saved from a grim prognosis in the nick of time using CRISPR technology. They created a personalized gene therapy specifically for Baby KJ’s unique genetic mutation, a feat which they accomplished in less than a year, compared to the typical seven to eight years such development usually requires. “This was the first time ever that somebody had done a gene editing,… one that was precisely made to cure his particular mutation and nobody else's,” explains Kolata.

The treatment used CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats) technology in which the Cas9 protein acts as an enzyme or a pair of “scissors” to make a precise, single-base change in Baby KJ’s DNA. CRISPR was first discovered in bacteria and archaea as part of their acquired immunity. Research found the complementary DNA strand for viruses that bacteria had been previously exposed to sandwiched in between repetitive sequences of DNA. The CRISPR enzyme would move along the bacteria’s DNA until it found the repeated sequence and then lyse the DNA. The enzyme would then move to the virus’ DNA and if the template strand was detected, the CRISPR enzyme would cut the DNA, preventing it from replicating and spreading the virus.

Since then, researchers were able to apply this discovery to the development of CRISPR-Cas9 technology. Since the entire human genome has been sequenced, doctors are able to pinpoint the exact spot where a mutation has occurred and create a complementary strand. This complementary strand is put into the CRISPR enzyme which allows it to crawl along the DNA until it precisely locates the targeted DNA sequence. From that point, there are two ways to proceed. If the DNA needs to be cut in that location to disable the DNA from being transcribed, translated, and duplicated, the CRISPR enzyme will lyse the DNA. However, if a single nitrogenous base needs to be modified, the CRISPR enzyme will stay attached to the mutation’s location and allow a base editor to replace the nitrogenous base, correcting the mutation.

In Baby KJ’s case, researchers proceeded with the second option, changing a single base in his DNA to treat his rare disorder. The gene editing machinery was delivered through lipid nanoparticles, similar to those used in mRNA COVID-19 vaccines, which protected the technology while it traveled through the bloodstream to target liver cells where the defective gene is expressed. Kolata describes CRISPR as a “GPS system, [which] points you to exactly that base, and then the machinery comes in and makes exactly one base change.” The lipid nanoparticles naturally migrate to the liver, where enzymes strip away the protective coating, allowing CRISPR machinery to begin working to correct the genetic defect. This is a significant advancement that improves patient safety and comfort, as opposed to traditional gene therapies that often require incredibly harsh treatments like chemotherapy to wipe out bone marrow before introducing modified cells. In direct contrast, Baby KJ’s treatment was very gentle, involving a simple infusion followed by monitoring and recovery. 

Behind the scientific breakthrough lies a story of extraordinary dedication. Researchers across the country worked around the clock, driven not by academic glory but by a genuine passion and singular mission to save a child's life. "One guy said he was in California and he said, 'we burned midnight oil like the size of the San Francisco Bay getting this done,'" Kolata recalls from her interviews with the research team. "All of us said this was the proudest moment in our lives to get this done." The emotional weight of the endeavor was equally immense. Baby KJ’s doctor purportedly looked his parents in the eye and conveyed the uncertainty of the experimental nature of this therapy. The alternative, doing nothing, would mean that they would have to watch their child suffer severe brain damage or death, which is why the parents agreed to this last resort. “For the doctors, everything was on the line," Kolata notes. "They worked like crazy night and day for months and months all over the country, and they didn't know for sure whether it was going to actually make a difference.”

New York Times Senior Reporter Gina Kolata who is responsible for the Baby KJ case

However, the Baby KJ case raises important ethical questions about experimental treatments, informed consent, and the responsibilities of medical researchers. When facing a terminal diagnosis with no established treatment options, how much risk is acceptable? How do doctors adequately convey both hope and uncertainty to desperate families? "One of the questions is always safety and how much information can you give people about safety," Kolata observes. She points out that the parties involved often have to grapple with the fact that “sometimes doing nothing is a better option for you than doing something.” It is a question of informed consent. How do you tell people who only want to hear 'you can help me' that maybe they should think about the risks?" 

The case also highlights the broader ethical landscape surrounding genetic editing. While Baby KJ's treatment focused on correcting a life-threatening defect, the same technology could theoretically be used for genetic enhancement—making children taller, smarter, or more attractive. These “designer babies”—babies who are modified genetically for aesthetic purposes and not due to medical need would require edits to be made to an embryo. While you cannot edit the genetics of a pregnant woman’s fetus, you can modify the genetics of an IVF (in vitro fertilization) embryo—a fertilized egg that has gone through the early stages of cellular division in a laboratory. Nevertheless, Kolata reminds us that “this is all hypothetical” as “scientists don’t know of single genes or small groups of genes that could be modified to make a person smarter or more beautiful or even to make them thinner.” Moreover, since this editing would affect the germ line cells, this change would become heritable. Due to the risks involved with modifying heritable traits, many countries have banned gene-editing on germ line cells and some have outright banned genetic editing on human embryos. Such applications that require editing genes in embryos during in vitro fertilization will inevitably continue to raise questions about safety, equity, and the very nature of human improvement.

Baby KJ's treatment signals a new era in personalized medicine, particularly for rare diseases. His successful treatment gives hope to over 30 million patients in the U.S. that suffer from 1 of over 7,000 rare diseases. Given the rarity of these diseases, pharmaceutical companies are unwilling to spend extensive resources and years on an expensive treatment that will only benefit a tiny fraction of the population. With the ease and lower costs of CRISPR technology, gene-editing could save these patients’ lives with its personalized treatment. The approach taken, using CRISPR’s modular nature to target specific genetic defects, could be adapted for numerous conditions. "When you know what the gene is, you have the basic structure, you can just change the instructions of where it's going to go," Kolata explains. This modularity makes the technology remarkably versatile and potentially cost-effective once the basic infrastructure is established. Emerging techniques like "prime editing" offer even greater precision, allowing researchers to replace entire gene segments rather than just single bases. This advancement could address more complex genetic disorders like cystic fibrosis, where multiple different mutations can cause the same disease.

Despite much promise, significant obstacles remain and must be addressed before gene editing therapies become widely available. Funding is perhaps the biggest challenge, particularly for rare diseases that affect small patient populations. Small biotechnology companies developing these treatments struggle to secure adequate investment, while larger pharmaceutical companies often wait until technologies are more proven before entering the market. Regulatory uncertainty adds another layer of complexity. The FDA's requirements for approving gene editing therapies remain unclear, particularly for rare diseases where traditional large-scale clinical trials are impossible due to limited patient numbers. Kolata expresses hope that the FDA might scale back on the requirements for these therapies, owing to the small population. 

Public understanding and acceptance of gene editing technology is also a great barrier. Misconceptions about genetic modification, often fueled by social media misinformation, create resistance to potentially life-saving treatments. "People hear gene editing and they think somehow somebody's going to change all your genes instead of just fix one that's not working and cure a horrible disease," Kolata observes. The challenge lies in educating the public about the precision and limited scope of therapeutic gene editing while addressing legitimate safety concerns.

A particular case that has gained much traction with bioethicists was when Chinese scientist He Jiankui from the Southern University of Science and Technology in Shenzhen, China attempted to alter the cells of twin baby girls to make them resistant to HIV (Normile, 2018). He genetically modified the embryos of 7 families, and was able to have 2 embryos implanted into two mothers. One mother gave birth to twin girls, but it is not clear whether the other mother’s child was born. In each case, the father was infected with HIV while the mothers were HIV-negative. His goal was to introduce a rare genetic variation that hinders the HIV from infecting its most common target, white blood cells. He used the CRISPR-Cas9 technique to delete an area of a receptor on the surface of a white blood cell known as CCR5. However, the CCR5 gene is also related to major brain functions, so editing this gene risked damage to the girls’ brain function.

He was not attempting to prevent the rare event of HIV transmission to the embryo from the father’s sperm. Rather, he was simply trying to make the girls HIV resistant. Even so, his attempt garnered much backlash from the scientific and ethics community. Many were concerned that these otherwise completely healthy baby girls would suffer side-effects from the unnecessary treatment since gene editing is experimental and associated with unintended mutations both early on and later in life. Others also expressed concerns over whether or not the parents were adequately informed of the risks of this treatment, including the low probability of HIV transmission from the father to the girls. Furthermore, since he altered the genome in the early stages of the embryo, the treatment affected the germ line cells, making the trait heritable. Consequently, any side effects or health issues that result from this treatment could be inherited which may cause issues for future generations. 

All of this controversy led the university to launch an investigation into He’s research. Because he misled doctors into implanting genetically edited embryos, He Jiankui was later found guilty of “illegal medical practices” and sentenced to 3 years in prison. This case may quell the nerves of those with anxieties about the treatment of embryos, as He’s experiment was widely condemned, creating stricter medical legislation in many countries including China, the United States, Canada, and Sweden.

Meanwhile, Baby KJ went home for the first time on June 3rd—a simple sentence that represents a medical miracle. His successful treatment demonstrates that personalized gene therapy is not science fiction but present-day reality. The case establishes a new paradigm for treating rare genetic disorders, one that could benefit thousands of children born with previously incurable conditions. The broader implications extend beyond rare diseases. As our understanding of genetics advances and gene editing technologies become more sophisticated and accessible, we may be witnessing the dawn of truly personalized medicine—treatments designed not just for specific diseases, but for specific individuals. The story of Baby KJ reminds us that behind every medical breakthrough are dedicated researchers, courageous families, and children whose lives hang in the balance. It represents hope for countless families facing genetic diseases, while also challenging us to thoughtfully navigate the ethical and practical complexities of our rapidly advancing genetic capabilities.

As gene editing technology continues to evolve, the questions raised by Baby KJ's case will only become more pressing: How do we ensure equitable access to these therapies? How do we balance innovation with safety? Additionally, how do we help society understand and embrace the responsible use of technologies that can literally rewrite the code of life? The answers to these questions will shape not just the future of medicine, but the future of humanity itself. Baby KJ's story is just the beginning.

References

Gostimskaya I. (2022). CRISPR-Cas9: A History of Its Discovery and Ethical Considerations of Its Use in Genome Editing. Biochemistry. Biokhimiia, 87(8), 777–788. https://doi.org/10.1134/S0006297922080090

Kolata, G. (2025, June 3).

Normile, D. (2018, November 26). CRISPR bombshell: Chinese Researcher Claims to Have Created gene-edited Twins. Www.science.org; Science. https://www.science.org/content/article/crispr-bombshell-chinese-researcher-claims-have-created-gene-edited-twins

Redman, M., King, A., Watson, C., & King, D. (2016). What is CRISPR/Cas9?. Archives of disease in childhood. Education and practice edition, 101(4), 213–215. https://doi.org/10.1136/archdischild-2016-310459