A genetic disorder is a disease caused by a mutation or change in an individual’s DNA. Sometimes a whole or part of a gene is defective or missing from birth or can mutate later in life, which can disrupt how proteins are made. This affects the body’s systems and causes health problems and diseases, such as sickle cell, SCID, and cancer. Majority of treatment strategies, for genetic disorders, do not alter the underlying genetic mutation, however a few have been treated with gene therapy (U.S national library of medicine,2020). This experimental technique uses genes to treat or prevent diseases. It offers the possibility to alter the genes, inside or outside of a patient’s cells, with the aim to cure a disease or help the body better fight disease (SVAR life science, 2019).
The first clinical trials were initiated in 1990 and published in 1995. They consisted of ex vivo gene transfer to the umbilical cord blood cells, for children suffering with SCID (due to mutations in the ADA gene). In these early studies, gene transfer protocols were inefficient and unable to convert hematopoietic stem cells (HSC). Therefore, limiting the duration of gene transfer. Since 1990, approximately 1500 clinical trials have been approved globally, using both viral and non-viral vectors and targeting various organs, cell types and diseases (Ronald W Herzog etal, US national library of medicine,2010).
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The X-linked type of SCID (SCID-X1) is the product of common cytokine receptor mutations. Without intervention, patients have a very poor prognosis and typically die of chronic and opportunistic infections within the first year of life. Since 2000, 20 children in France and the United Kingdom took part in gene therapy trials. Cytoreductive conditioning was not used on patients as there was an expectation that in an otherwise empty area, gene-modified T-cell progenitors would have a high survival rate. Following up to the study, eighteen out of twenty participants were alive after an average follow up of 80 months in the U.K and nine years in France. Majority of the patients showed almost normal numbers and functioning of T cells. Nevertheless, recovery of humoral immunity varied as there was a divide amongst patients, with almost half of the patients being able to discontinue immunoglobulin replacement therapy. Furthermore, four out of ten children in the French trial and one out ten in the trial in the UK developed Leukaemia. Integration of the cancerous genes were shown near the LMO2 T cell oncogene. There is a high possibility that the growth of gene corrected T cells and LMO2 caused this result. Although retroviral vectors integrate spontaneously into the host genome, they evidently hold a preference for active genes (Ronald W Herzog, US National Library of Medicine, 2010).
On the other hand, retroviral transduction of HSC, continues to show positive therapeutic efficacy, without producing leukaemia. In an Italian trial eight of ten patients had been cured and they no longer require enzyme replacement therapy. The children continue to live normal healthy lives, no longer having to be sheltered heavily as “bubble children”. The treatment consisted of mild bone marrow conditioning with busulfan, meanwhile ADA enzyme replacement therapy was stopped to increase engraftment of modified gene cells and provide an advantage in growth over non modified gene cells. This led to a correction of many hematopoietic lineages. In lymphocytes and red blood cells, the ADA transgene was expressed, thereby contributing to systemic detoxification and immune function regeneration.
Most diseases treated with gene therapy are inherited genetic diseases, however gene therapy is also used to treat certain cancers and viral infections. Therefore, gene therapy currently at its best is only useful for a select subset of genetic disorders. Chromosomal aneuploidy, such as down syndrome is not currently curable by gene therapy (Rosenberg, Genetics and the law III, 2013). Down Syndrome affects around six million people worldwide. The genetic disorder hinders physical growth and intelligence, causing serious medical problems, such as heart defects and early dementia (R. Young, NPR,2013). Somatic avenues for treating Down Syndrome may be able to treat certain elements of the condition, such as the loss of nerve cells, which causes weak musculature. Nevertheless, difficulties arise in selecting the precise genes responsible for the characteristics, and then correctly and efficiently targeting them within the billions of relevant live cells to treat the condition. Researchers from the University of Massachusetts medical School faced this exact challenge, when devising a gene therapy treatment. In a study, conducted in 2014, researchers added an RNA gene (XIST) to human stem cells, which allowed them to “turn off” the extra chromosome, responsible for Down Syndrome. The XIST gene, added to the extra chromosome, ignited a build up of RNA, which eventually coated the extra chromosome and shut it down. However, for this study to be successful, the procedure would have to be replicated to across majority of cells in an organism- a task beyond current capabilities (Lennon, Labroots, 2019).
In conclusion, Gene Therapy has a very promising future, with the possibility of curing many life threatening and life altering diseases. It has had many clinical advancements over the past decade. LV and AAV vectors have had particularly positive advancements. Key information learned during recent trials will drive to many innovations to gene therapy approaches. Nevertheless, Gene Therapy is still at its early stages; a lot more research and trials are needed before it becomes a widely spread form of treatment.
Works Cited
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- “Gene Therapy Successes.” Utah.Edu, 2011, learn.genetics.utah.edu/content/genetherapy/success/.
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- “New Genetic Therapy Could Erase Down Syndrome.” NPR.org, www.npr.org/transcripts/203047251?t=1604062700145. Accessed 17 Nov. 2020.
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- Science, Svar Life. “What Is Gene Therapy and Which Diseases Can It Treat?” Www.Svarlifescience.com, www.svarlifescience.com/news/what-is-gene-therapy-definition. Accessed 17 Nov. 2020.
- “What Is Gene Therapy?: MedlinePlus Genetics.” Medlineplus.Gov, medlineplus.gov/genetics/understanding/therapy/genetherapy/#:~:text=Gene%20therapy%20is%20an%20experimental.
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- Zhang, L., et al. “Current Progress on Gene Therapy for Primary Immunodeficiencies.” Gene Therapy, vol. 20, no. 10, 1 Oct. 2013, pp. 963–969, www.nature.com/articles/gt201321, 10.1038/gt.2013.21. Accessed 17 Nov. 2020.
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