By: Lauren Wilkes, Biological Sciences ‘27
Brittle Bones Disease, as its name suggests, may seem like an arthritis-related problem easily resolved with some physical therapy or painkillers. However, Brittle Bones Disease, scientifically referred to as Osteogenesis imperfecta (OI), is generally classified as an incurable genetic disease. Despite innovations in biomedical technology, one may wonder why genetic cures on the cellular level for Brittle Bones Disease have not been developed yet. A quick Google search, however, will reveal that active research is being conducted to explore the potential for using CRISPR, a gene-editing technology, to help “fix” the mutated gene causing Brittle Bones Disease.
Osteogenesis imperfecta is a genetic disease in which bones are more susceptible to breaking easily [1]. The disease can result in numerous complications, from minimal hairline fractures to detrimental breakages [1]. In unaffected individuals, normal bone strength comes from and is maintained via collagen; the production of which is controlled by a specific gene, called COL1A1. Brittle Bones Disease has been traced back to a genetic mutation in this gene in humans, leading to either an absence of or impaired collagen production. The mutation prevents COL1A1 from producing the same amount of collagen as is necessary to maintain high bone mineral density to prevent easy breakages [2]. The lack of collagen production, therefore, leads to weaker bones that are more susceptible to fractures. Because this has been identified as a genetic mutation, active research is underway to investigate the potential for using the gene-editing technology CRISPR-Cas9 to edit and splice out the mutated genome, thereby correcting it [3].
CRISPR, short for “Clustered Regularly Interspaced Short Palindromic Repeats,” is a gene editing technology that has proven useful in recent years in correcting errors in genetic sequences [4]. The functionality of the CRISPR complex works in stages including the recognition, cleavage, and repairing stages, respectively. CRISPR uses an enzyme, Cas9, which is the driving force behind the ability for CRISPR to actually cut, splice, and correct these erroneous sequences. Cas9 is a protein that has the ability to recognize a specific binding side on a DNA sequence [5]. Upon binding to that sequence, the enzyme executes the cleavage stage by splicing out a piece of the genome. The repair stage is then executed through Cas9 either inserting a new piece of a sequence, or repairing the broken sequence to complete the newly edited DNA strand [6]. CRISPR-Cas9 has opened up a myriad of opportunities for curing previously incurable genetic diseases, particularly due to the fact that it has demonstrated its efficacy in mammalian organisms [6]. In the recent past, in May 2017, for instance, researchers at Temple University successfully demonstrated that CRISPR could be utilized to excise the genome of the HIV-1 virus to completely shut down the replication of the HIV virus in animals [6]. In this way, the efficacy of CRISPR has been demonstrated on occasions in the recent past and thus provides us with insight into its efficacy in humans. However, one of the reasons for research regarding CRISPR’s application for treating genetic diseases like OI is the need to confirm its efficacy and safety for use on humans.
In the case of correcting the COL1A1 mutation in OI patients, the pathway would proceed as follows: since the COL1A1 collagen-producing gene is dominant, it will have a higher likelihood of being passed on from generation to generation. Furthermore, the COL1A1 mutation that causes Osteogenesis imperfecta presents itself as a switch to a different protein that causes abnormal collagen to be distributed to bones, reducing bone strength. To correct this, CRISPR-Cas9 will cut and delete the mutated gene, changing the frame of the COL1A1 sequence to produce the normal protein which allows for normal collagen production to resume [7].
Given that COL1A1 is a dominant gene, this procedure would have especially vital implications for Osteogenesis Imperfecta patients in that the corrected gene would be the one most likely passed on to the next generation due to its dominance. If, ultimately, after conducting research to verify the safety to the surrounding cellular environment in addition to the targeted cells, using CRISPR-Cas9 as a curative measure is determined to be safe and effective, CRISPR-edited and corrected COL1A1 would be placed in pluripotent stem cells, or cells that “have the ability to undergo self-renewal and to give rise to all cells of the tissues of the body,” to then be given to Brittle Bones Disease patients [8].
CRISPR falls into that vast and highly debated category of gene editing, making CRISPR a novel yet controversial technique due to bioethical concerns surrounding our lack of knowledge on its effects in humans, as it has been mainly researched in model mammalian organisms. However, when applicable and efficacious for curing the incurable, it is more than worth a shot [9].
Although it is estimated that only around one in every 10,000 individuals is affected by Brittle Bones Disease, its incurable and more importantly, hereditary nature makes it more than worth furthering our exploration of this genetics-based cure [10]. Individuals affected by Osteogenesis imperfecta would have a chance now to re-engineer the problem that is inevitably already engineered against them and their bodies. Thus, not only would CRISPR play an instrumental role in curing OI for the currently affected patients, but the many future generations that would have been affected.
References
[1] Botor, M., Fus-Kujawa, A., Uroczynska, M., Stepien, K. L., Galicka, A., Gawron, K., & Sieron, A. L. (2021). Osteogenesis Imperfecta: Current and Prospective Therapies. Biomolecules, 11(10), 1493. https://doi.org/10.3390/biom11101493
[2] Seto, T., Yamamoto, T., Shimojima, K., & Shintaku, H. (2017). A novel COL1A1 mutation in a family with osteogenesis imperfecta associated with phenotypic variabilities. Human Genome Variation, 4(1), 17007. https://doi.org/10.1038/hgv.2017.7
[3] Jung, H., Rim, Y. A., Park, N., Nam, Y., & Ju, J. H. (2021). Restoration of Osteogenesis by CRISPR/Cas9 Genome Editing of the Mutated COL1A1 Gene in Osteogenesis Imperfecta. Journal of clinical medicine, 10(14), 3141. https://doi.org/10.3390/jcm10143141
[4] Questions and answers about crispr. (n.d.). The Broad Institute. https://www.broadinstitute.org/what-broad/areas-focus/project-spotlight/questions-and-answers-about-crispr
[5] Uslu, M., Siyah, P., Harvey, A. J., & Kocabaş, F. (2021). Chapter Six—Modulating Cas9 activity for precision gene editing. In V. Singh (Ed.), Progress in Molecular Biology and Translational Science (Vol. 181, pp. 89–127). Academic Press. https://doi.org/10.1016/bs.pmbts.2021.01.015
[6] Asmamaw, M., & Zawdie, B. (2021). Mechanism and Applications of CRISPR/Cas-9-Mediated Genome Editing. Biologics : targets & therapy, 15, 353–361. https://doi.org/10.2147/BTT.S326422
[7] The COL1A1 Gene. (n.d.). National Library of Medicine: Medline Plus . https://medlineplus.gov/genetics/gene/col1a1/#conditions
[8] Romito, A., & Cobellis, G. (2016). Pluripotent Stem Cells: Current Understanding and Future Directions. Stem cells international, 2016, 9451492. https://doi.org/10.1155/2016/9451492
[9] Ayanoğlu, F. B., Elçin, A. E., & Elçin, Y. M. (2020). Bioethical issues in genome editing by CRISPR-Cas9 technology. Turkish journal of biology = Turk biyoloji dergisi, 44(2), 110–120. https://doi.org/10.3906/biy-1912-52
[10] Osteogenesis imperfecta. (2022, July 19). https://www.hopkinsmedicine.org/health/conditions-and-diseases/osteogenesis-imperfecta
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