Genomics: Insight

Research Question: What are the benefits of CRISPR-Cas9 and what policies should be implemented to regulate the use of CRISPR-Cas9 for gene editing in diseases and gene therapy, and where should ethical boundaries be drawn to address societal inequalities?

Introduction: A brief overview of CRISPR-Cas9 technology and its transformative potential

CRISPR, short for ‘clustered regularly interspaced short palindromic repeat’, primarily  discovered by Dr. Jennifer Doudna and Dr. Emmanuelle Charpentier is one of the most advanced gene editing tools currently available to scientists. This 2020 Nobel Prize in Chemistry winning technology allows a researcher to target specific sequences on any organism’s DNA and modify it. CRISPR-Cas9, which is what will be discussed in this review specifically, has an enzyme called Cas9 that is specifically used to cut various DNA sequences. Cas9 binds to a three-nucleotide sequence that is abundant throughout the genome called “PAM” (prospector adjacent motif,) then it unwinds the DNA double helix. If the DNA at that location matches with the guide RNA, they will bind together through base pairing. This pairing instructs the Cas9 protein to change its structure and cleaves both DNA strands at a site upstream of the PAM, and this cleaving is one of the main functions of CRISPR-Cas9.

CRISPR-Cas9 offers the potential to address thousands of genetic mutations that cause diseases by precisely altering specific DNA sequences. This provides the opportunities to prevent, treat, and even eliminate these diseases entirely. Scientists have already taken advantage of CRISPR-Cas9 for all different types of diseases. Sickle Cell and Beta-Thalassemia, Retinal Dystrophies, and Hereditary Tyrosinemia, have all been treated by CRISPR-Cas9. Gene editing technology that was used prior to CRISPR-Cas9, such as Transcription Activator-Like Effector Nucleases (TALENs) and Zinc-Finger Endonucleases (ZFNs) were not nearly as efficient as Cas9 because of their time consuming, labor intensive processes ³, which is why CRISPR-Cas9 is such a revolutionary tool. However, the controversial topic of Designer Babies arises when CRISPR-Cas9 is discussed because using CRISPR-Cas9 to genetically modify embryos, children, and fetuses, all of which are considered distinct by the NASEM (National Association of Science, Engineering, and Math), before birth brings up ethical concerns within the science community.⁵

CRISPR-Cas9 in Medicine: Transformative Applications

Sickle Cell and β-Thalassemia

The BCL11A switch activates the creation of the BCL11A protein which regulates the production of gamma globin. Gamma-globin is produced instead of beta globin for fetal hemoglobin. After birth, BCL11A protein increases resulting in decreased production of gamma globin; therefore, the mutated beta globin is used to make most of the hemoglobin. In patients with Sickle cell and B Thalassemia where the Beta Globin genes are mutated, removing restrictions on the gamma globin protein by disrupting the BCL11A gene had proven to be an effective treatment. The disruption of this switch in a clinical trial through CRISPR-Cas9 led to one patient increasing fetal hemoglobin levels from 0.3 g per deciliter at baseline to 8.4 g per deciliter at month 3, 12.4 g per deciliter at month 12, and 13.1 g per deciliter at month 18 as well as an increase in F-cell expression from 10.1% at baseline to a static 99.7% at month 6. These increases led to a reduction in the need for transfusions that the patient had needed since childhood. The second patient suffered from sickle cell disease. After the treatment of replacing her stem cells with the genetically engineered ones with the BCL11A switch mutated, her sickle hemoglobin decreased by 21.8 percent and a 34.1 percent increase in fetal hemoglobin. As a result of the treatment, she had no vaso-occlusive episodes, a painful symptom of sickle cell disease.²

Tyrosinemia

Tyrosinemia is a genetic disorder recognized by problems breaking down tyrosine, an amino acid present in many proteins, leading to a harmful buildup of tyrosine in tissues and organs. Scientists working with rats with the condition targeted the mutated gene which causes the issue, a 10-base pair deletion in the Fah gene. Using CRISPR-Cas9 to break apart the mutated gene as well as delivering a repair template of the healthy gene. After a monitoring period of 9 months post-treatment, the treated rats gradually gained weight and liver damage markers such as AST and ALT were substantially decreased from baseline to normal levels. Contrastingly, none of the untreated control rats survived past day 40 of the beginning of the experiment, indicating the success in repairing the gene.⁴ Currently, this treatment has yet to be applied in humans as more research about potential adverse side effects needs to be done. One of the possible adverse effects is the potential to develop liver cancer as a result of the treatment. A study by scientists in the genetic and medical field found that rats cured by CRISPR Cas-9  were much more likely to develop liver cancer as a result of their treatment. Specifically 71%  of the rats, or 12 out of the 17, were found to have developed liver cancer as a result of the treatment.⁶

Herpetic Stromal Keratitis

Herpetic Stromal Keratitis is a condition that can develop from being infected with herpes simplex virus 1 (HSV-1) causing severe loss of vision. CRISPR-Cas9 targeted the UL8 gene, which is important for viral DNA replication, and the UL29 gene, which is critical for viral genome processing and replication in the viral DNA inside the corneas of three patients. After the injection of the herpes simplex virus I (HSV-1)-targeting CRISPR into the corneas, Patient 1 improved their vision from only having light perception to having 20/100 vision. Patient 2 improved from only visualizing hand motion to stabilizing a little under 20/100 vision. Patient 3 improved from hand motion visualization to being able to recognize a finger count. All three patients made vast improvements in the 12 months post treatment.⁷

Retinal Dystrophies

Retinal Dystrophies (RDs) are degenerative diseases in the retina of eyes which can lead to vision loss. This study looks to correct the mutation in the rhodopsin gene (Rho^S334) responsible for retinitis pigmentosa using the CRISPR-Cas9 system. Treated rats retained around 45% normal rod function while untreated rats only had around 20% normal rod function. Treated eyes retained about 4–5 rows of photoreceptor nuclei, while untreated eyes had only 1–2 rows at the same time point.¹

Stages of Treatment

Impact

As a result of CRISPR-Cas9, many debilitating illnesses and mutations have been addressed, therefore, allowing people to live normal lives despite these issues.
 

The Ethics of CRISPR-Cas9: Boundaries and Risks

A designer baby is a baby whose genetic makeup has been selected or altered, often to exclude a particular gene or to remove genes associated with disease. It involves modifying the genetic makeup of embryos, which is made easier with the use of CRISPR-Cas9.

The concept of designer babies introduces a series of ethical issues, one of the main ones being that unborn children cannot consent to any genetic modifications. Another issue that arises is that with designer babies, the medical field might start using children as commodities, such as in the case of “saviour babies”, where embryos are created to provide a cure for a sibling. Informed consent ensures that individuals fully understand the procedures, risks, and potential benefits of genetic modification is essential. There are also potential unknown risks or health issues from genetic modifications, such as cancer, allergens, and death.³ While CRISPR-Cas9 is an extremely useful tool, the need for regulation is needed in order to ensure that its usage remains ethical.
 

Policy Recommendations for Regulating CRISPR-Cas9

While CRISPR-Cas9 can be an incredible gene editing tool for medical issues and other areas, like genetically modified plants, it should not be used for aesthetic reasons. A possible policy regarding this issue might state that CRISPR-Cas9 should only be used in the case of serious health issues regarding genetic mutation. To ensure that CRISPR-Cas9 is used practically, regulations regarding informed consent should be upheld to the highest standard.
 

Conclusion

CRISPR-Cas9, discovered by Dr. Jennifer Doudna and Dr. Emmanuelle Charpentier, is a groundbreaking tool that enables precise gene editing to target genetic diseases. It has proved to be successful in case studies revolving Sickle Cell Disease and β-Thalassemia, Tyrosinemia, Herpetic Stromal, Keratitis, Retinal Dystrophies. While CRISPR-Cas9 offers the potential to treat thousands of genetic conditions, it raises ethical concerns about misuse for non-medical purposes. Despite its transformative potential, CRISPR-Cas9's application must carefully balance medical innovation with ethical considerations to prevent harm.

 "CRISPR's application must carefully balance medical innovation with ethical considerations."

References

1. Bakondi B, Lv W, Lu B, Jones MK, Tsai Y, Kim KJ, Levy R, Akhtar AA, Breunig JJ, Svendsen CN, Wang S. In Vivo CRISPR/Cas9 Gene Editing Corrects Retinal Dystrophy in the S334ter-3 Rat Model of Autosomal Dominant Retinitis Pigmentosa. Mol Ther. 2016 Mar;24(3):556-63. doi: 10.1038/mt.2015.220. Epub 2015 Dec 15. PMID: 26666451; PMCID: PMC4786918.
2. Frangoul H, Altshuler D, Cappellini MD, Chen YS, Domm J, Eustace BK, Foell J, de la Fuente J, Grupp S, Handgretinger R, Ho TW, Kattamis A, Kernytsky A, Lekstrom-Himes J, Li AM, Locatelli F, Mapara MY, de Montalembert M, Rondelli D, Sharma A, Sheth S, Soni S, Steinberg MH, Wall D, Yen A, Corbacioglu S. CRISPR-Cas9 Gene Editing for Sickle Cell Disease and β-Thalassemia. N Engl J Med. 2021 Jan 21;384(3):252-260. doi: 10.1056/NEJMoa2031054.
3. Gaj T, Sirk SJ, Shui S-L, Liu J. Genome-editing technologies: Principles and applications [Internet]. U.S. National Library of Medicine; 2016 [cited 2025 Mar 19]. Available from: https://pmc.ncbi.nlm.nih.gov/articles/PMC5131771/#:~:text=The%20core%20technologies%20now%20most,)%2C%20and%20(4)%20homing
4. Saravanan S, N HP [Internet]. [cited 2025 Feb 13]. Available from: https://www.researchgate.net/publication/372886989_Designer_Babies_Revealing_the_Ethical_and_Social_Implications_of_Genetic_Engineering_in_Human_Embryos_IJSR_Volume_12_Issue_7_July_2023
5. Shao Y, Wang L, Guo N, Wang S, Yang L, Li Y, Wang M, Yin S, Han H, Zeng L, Zhang L, Hui L, Ding Q, Zhang J, Geng H, Liu M, Li D. Cas9-nickase-mediated genome editing corrects hereditary tyrosinemia in rats. J Biol Chem. 2018 May 4;293(18):6883-6892. doi: 10.1074/jbc.RA117.000347. Epub 2018 Mar 5. Erratum in: J Biol Chem. 2019 May 24;294(21):8348. doi: 10.1074/jbc.AAC119.009120. PMID: 29507093; PMCID: PMC5936814.
6. Steynberg R. Evaluating the ethics of human gene editing [Internet]. [cited 2025 Feb 13]. Available from: https://journals.tulane.edu/ncs/article/view/3785/3553
7. Tong Chen, Mercedes Barzi, Nika Furey, Hyunjae R. Kim, Francis P. Pankowicz, Xavier Legras, Sara H. Elsea, Ayrea E. Hurley, Diane Yang, David A. Wheeler, Malgorzata Borowiak, Beatrice Bissig-Choisat, Pavel Sumazin, Karl-Dimiter Bissig, CRISPR/Cas9 gene therapy increases the risk of tumorigenesis in the mouse model of hereditary tyrosinemia type I, JHEP Reports, 2025, 101327, ISSN 2589-5559, https://doi.org/10.1016/j.jhepr.2025.101327.
8. Wei A, Yin D, Zhai Z, Ling S, Le H, Tian L, Xu J, Paludan SR, Cai Y, Hong J. In vivo CRISPR gene editing in patients with herpetic stromal keratitis. Mol Ther. 2023 Nov 1;31(11):3163-3175. doi: 10.1016/j.ymthe.2023.08.021. Epub 2023 Aug 31. PMID: 37658603; PMCID: PMC10638052.