Friday, 25 May 2012

Gene Therapy Technique to Cure Retinitis Pigmentosa

Just earlier this year, scientists from the University of Pennsylvania have discovered a gene therapy technique that could potentially cure a common retinal genetic disease. The study, which results from more than ten years of collaboration between scientists from various universities, is yet to be published in the ‘Proceedings of National Academy of Sciences’ journal. The soon to be released journal proposes gene therapy as a therapeutic strategy on dogs that have the Retinitis Pigmentosa disease (Science Daily 2012).

Figure 1: Tunnel vision view as from perspective of person with
Retinitis Pigmentosa (Gelder, Joosten & Sminia)
Retinitis Pigmentosa is basically an X – linked ocular genetic disease caused by a mutation on the Retinitis Pigmentosa GTPase Regulator (RPGR) gene. It is the leading cause of all retinal inherited blindness, affecting 1.5 million people worldwide. The defect gene basically denotes the loss of vision (Science Daily 2012). In the early stages of Retinitis Pigmentosa, the loss of peripheral and night vision is most commonly experienced, followed by the narrowing of the eye’s visual field (also known as tunnel vision) before the individual becomes completely blind (Science Daily 2012).

Figure 2: Microscopic view of cells in healthy retina (left) and retina after
onset of Retinitis Pigmentosa (Fariss & Milam 2009) 

Usually, our ability to ‘see’ begins in the photoreceptor cells. In order for this to happen, the rods and cones in our retinas need to absorb photons from light to trigger a change in the cell membrane’s potential. It is the difference in the cell membrane’s potential that acts as information for the brain to make representations of the visual world (Darling). However, with the gradual degeneration of photoreceptive cells as characterized by Retinitis Pigmentosa, the retina no longer remains viable to process or send visual information to the brain, resulting in partial or complete 
blindness (Bionic Vision Australia). 
Figure 3: (a)  Interior surface of a normal human retina (left) and (b) interior surface of retina of a patient diagnosed with Retinitis Pigmentosa (right) – pigmentation represents clumping of epithelium cells from degeneration of photoreceptive cells (Creel 2007)

To rectify this problem, scientists cloned a functioning copy of the RPGR gene and injected it into a viral vector that delivered the working RPGR gene to only the infected rod and cone photoreceptive cells in the retina of a dog. This effectively replaced the malfunctioning RPGR gene primarily involved in the degeneration of the photoreceptive cells. Additionally, a promoter (a sequence of nucleotides) was cloned which enabled the activation of the working RPGR gene once the virus penetrated into the target cells.

By the end of the study, results revealed that the administered injection of the virus led to functional and structural recovery of the photoreceptor cells in the dog’s retina. The cells that contained the new working gene expressed normal functioning which meant that not only did scientists find a way to prevent the disease onset, but also restore the defective cells that existed in the retina. In order for the treatment to be used in humans, more tests must be conducted on long – term efficiency and safety before it moves into clinical trials.

Reference List:
 Darling, D, Photoreceptor Cell, viewed 18 March 2012, <>
Science Daily 2012, Gene Therapy Cures Retinitis Pigmentosa in Dogs, Viewed 16 March 2012,
 Science Daily 2012, Researchers Develop Gene Therapy That Could Correct a Common Form of Blindness, Viewed 16 March 2012, <>
 Bionic Vision Australia, Retinitis pigmentosa, Viewed 17 March 2012,
Stieger, K 2010, ‘Gene Therapy for Vision Loss – Recent Developments’, Discovery Medicine, viewed 17 March 2012,

National Institutes of Health, National Human Genome Research Institue1999, Understanding Human Genetic Variation, viewed 15 March 2012, <>

Figure 1:
Gelder, C, Joosten, R & Sminia, H n.d., Retinitis pigmentosa, bioinformatics@school, Netherlands, viewed
Figure 2:
Fariss, R & Milam,  A 2009,  Damaged Rods and Cones, Nataional Eye Institute, USA, viewed 17 March 2012, < >
Figure 3(a):
Creel, D. 2011, Fundus photo of a normal human retina, Webvision, USA, viewed 16 March 2012, <>
Figure 3(b):
Creel, D. 2011, Fundus photo of a patient with retinitis pigmentosa, Webvision, USA, viewed 16 March 2012, <>


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