Overview of CRISPR
CRISPR is an innovative tool making significant impacts in medicine and changing lives. CRISPR, an acronym for “Clustered Regularly Interspaced Short Palindromic Repeats,” exists in prokaryotes—tiny, single-celled organisms lacking organelles. These sequences can be found in the genomes of prokaryotes, where they collect a cell’s DNA in clusters.
As a gene-editing mechanism, CRISPR is utilized to alter specific DNA segments to address serious illnesses. It is especially valuable as it protects the body against viral attacks by integrating the foreign DNA into its own genome, equipping it to identify and eliminate the virus in subsequent encounters. Notably, in comparison to other gene editing techniques, CRISPR is significantly more accurate and easier to configure, facilitating a more straightforward sequence modification process. While traditional gene-editing tools usually rely on a single protein, CRISPR employs RNA-guided targeting along with the Cas9 enzyme.
Mechanism of CRISPR
CRISPR operates by leveraging a natural defense strategy observed in bacteria that enables them to detect and eliminate viral threats. Upon a viral invasion of a bacterial cell (a prokaryote), the bacterium retains a segment of the invader’s DNA in its own genome as a genetic “memory.” This allows the bacterium to identify and react more efficiently to subsequent infections.
In gene editing, this mechanism is modified with two essential elements: the Cas9 enzyme that acts like molecular scissors to cleave DNA, and guide RNA, which directs Cas9 to the particular genetic sequence intended for modification. After the targeted DNA is severed, the cell’s inherent repair systems take charge, allowing researchers to implement alterations to the genetic material.
In contrast to earlier tools which depended on difficult-to-reprogram proteins, CRISPR’s RNA-guided method is more adaptable, easier to create, and highly accurate. This combined simplicity and precision have enabled CRISPR’s application in disciplines such as medicine, agriculture, manufacturing, and microbiology—like designing microbes to enhance product yields. However, as this article discusses, the expansion of capabilities brings forth increasing ethical dilemmas, particularly concerning germline editing and genetic enhancement.
The World’s Pioneering Patient of Personalized CRISPR Therapy
In February 2025, the first-ever personalized CRISPR therapy was administered to an infant named KJ to address a deficiency in Carbamoyl Phosphate Synthetase 1 (CPS1)—an enzyme essential for converting ammonia (produced during protein metabolism) into urea. A research group led by Dr. Rebecca Ahrens-Nicklas and Dr. Kiran Musunuru at the Children’s Hospital of Philadelphia developed this therapy following extensive gene editing research and collaboration with other medical professionals.
Their research concentrated on conditions impacting the urea cycle, which results in toxic ammonia accumulation, causing harm to organs such as the brain and liver. They customized the therapy specifically for KJ’s variant of CPS1 deficiency, informed by preclinical studies on analogous variants.
To date, the only CRISPR therapies authorized by the U.S. FDA are for more prevalent conditions like sickle cell disease and beta thalassemia, which impact tens of thousands of individuals. KJ’s therapy was formulated within six months of his birth, focusing on his particular CPS1 variant. The team produced a base editing treatment delivered via lipid nanoparticles targeting his liver to rectify the malfunctioning enzyme.
The February treatment marked the first of three administrations; KJ received the subsequent doses in March and April of 2025. As of his last dose, he has not encountered any severe side effects, exhibits higher tolerance to dietary protein, and requires a reduced amount of medication to control ammonia levels. Although ongoing monitoring will be essential, Ahrens-Nicklas indicates that the outcomes thus far are encouraging.
Ethical Issues Surrounding CRISPR
Like any pioneering technology, CRISPR provokes intricate ethical discussions. While its main aim is to edit somatic cells to treat ailments, it can also be utilized on gametes, entering the contentious area of germline editing. Modifying DNA destined to be passed on to future generations is frequently deemed unethical—especially when aimed at enhancing specific traits rather