Gene Therapy - Eye Health Nepal

Gene Therapy

What is Gene Therapy? 

Gene therapy is a technique used in modern medicine wherein a foreign Deoxyribonucleic Acid (DNA) is introduced into host cells to treat or prevent illness. Although still in development, Gene Therapy is one of the most promising ventures of modern medical science in regard to the treatment of persistent and dominant genetic conditions.


Gene Therapy


How does gene therapy work? 

Any gene needs a vector to be delivered into the cell. The process of gene delivery is known as transduction. The most common vector used are viruses, which are introduced into the body via injection, or grafted onto the patient. The viruses are modified to not cause diseases in the host’s body once injected. Viruses can integrate the genetic material into the chromosome (retrovirus), or infect the cell and inject their DNA into the nucleus without affecting the chromosome (Adenovirus), which can then synthesize the protein that was affected due to mutated gene.


How does gene therapy work?



History

While the theories of Gene therapy were already in discussion in scientific communities from the early 1970s, the first gene therapy trial was approved in 1990 for a 4-year-old girl named Ashanti DeSilva. Her body lacked a vital enzyme called Adenosine deaminase (ADA), and as a result, she was highly susceptible to fatal infections, a condition called Severe Combined Immunodeficiency (SCID). 

The viral vector was used to introduce the ADA gene into her T cells, which resulted in a successful treatment.  

However, the field suffered a massive setback when in 1999, 18-year-old Jesse Gelsinger suffering from ornithine transcarbamylase deficiency died after four days of being injected due to severe immune reaction.

Fast forward two decades, Gene therapy has been developed for many diseases considered untreatable, such as cancer, Sickle cell anaemia, haemophilia, and show promising outcomes for neurogenetic diseases as well as AIDS. 


Gene Therapy For The Eye

The eye is a closed system, which doesn’t let vectors to move outside into the body. This is a reason why the eye is considered to be a suitable model for gene therapy.

One of the first breakthroughs of gene therapy in ocular diseases has been for Leber’s congenital amaurosis (LCA). LCA is an autosomal recessive genetic disorder due to mutation in The research on the gene RPE65 led to innovative technologies like LUXTURNA ( It is the first FDA-approved gene therapy for a genetic disease) which improved visual function and thus improves the quality of life of the patients.


This breakthrough has paved a way for phase one research for various other degenerations and diseases of the retina. Phase I clinical trials have begun for various other diseases too.

Age-Related Macular Degeneration (ARMD) in the wet stage shows neovascularization in the retina. The with gene therapy named ‘Retinostat’ and ‘sLFT’ have proven to be safe in the first phase. While Retinostat targets o production of protein to inhibit abnormal blood vessel formation, sLFT creates VEGF blocker. 

Gene Therapy and the EYe

Similarly, researches regarding gene therapy for Retinitis Pigmentosa (RP) on the retina of mice, dogs, etc. show promise, with gene therapy preserving photoreceptor cells and in reducing the progression of the disease. Autosomal dominant RP in the canine retina, when injected with a healthy RHO gene, has prevented degeneration from worsening. Similarly, X linked RP in canine models showed improvement in Photoreceptor cell condition when treated with gene therapy.

Researches are ongoing for other retinal diseases too, namely choroideremia, usher’s syndrome, Stargardt disease, etc.

Challenges for gene therapy for eye include diseases occurring due to genes that are too large to be carried by a vector. Similarly, further research is required to establish prognosis and effectivity of the therapy for both long and short term.




Article By: Manashwi Karki, Optometrist, ForOptom Nepal


References: 

1) MithaF.The Return of Gene Therapy. Labiotech.eu. 
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2) Gene Therapy Net. Diseases treated by gene therapy. 
Available from https://shorturl.at/hHMPW (accessed 2020 september 8)
3) Samiy N, Gene Therapy for Retinal Diseases. J Ophthalmic Vis Res. 2014 Oct-Dec; 9(4): 506–509. doi: 10.4103/2008-322X.150831. 
available from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4329713/ (accessed 2020 september 8) 
4) Cideciyan et al. Mutation-independent rhodopsin gene therapy by knockdown and replacement with a single AAV vector. Proc Natl AcadSci U S A. 2018 Sep 4; 115(36): E8547–E8556.Published online 2018 Aug 20. doi: 10.1073/pnas.1805055115
Available from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3277562/ (accessed 2020 september 13)
5) Beltran J et al. Gene therapy rescues photoreceptor blindness in dogs and paves the way for treating human X-linked retinitis pigmentosa. Proc Natl AcadSci U S A. 2012 Feb 7; 109(6): 2132–2137.Published online 2012 Jan 23. doi: 10.1073/pnas.1118847109 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5360787/


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