Tuesday, 3 April 2012

A Possible Cure for X-linked Retinitis Pigmentosa

Lisa Song (42895000)

Imagine knowing that you’re becoming increasingly blinder with each passing day and thinking that there was nothing you could do about it. This is what the 1.5 million patients of the current leading cause of inherited blindness, Retinitis Pigmentosa, go through on a daily basis [2]. The term Retinitis Pigmentosa is used to classify a group of genetic eye diseases which cause the loss of light-receptor cells, known as photoreceptors, in the retina [2]. As a result of the photoreceptor degeneration, the brain becomes unable to detect visual signals leading to visual impairment and occasionally blindness. X-linked Retinitis Pigmentosa is a common and severe form of Retinitis Pigmentosa which causes the majority of its patients to become legally blind by the time they’re 40 [5].

Figure 1 – Difference in photoreceptors (rods and cones) between a normal retina and the retina of a Retinitis Pigmentosa patient [7]

This disease is currently incurable. However, a study completed by scientists at the University of Florida and the University of Pennsylvania has made remarkable progress in changing this. The study resulted in the development of a potential cure for a common strand of X-linked Retinitis Pigmentosa [4]. This strand of X-linked Retinitis Pigmentosa is caused by a defect in the RTPase regulator (RPGR gene), which prevents the encoding of the photoreceptor ciliary protein [1]. Without the production of this protein, the photoreceptor cells degenerate and die, thus damaging the retina and causing the loss of vision. The scientists also believe that the deformity found in the RPGR gene is carried by females, who do not show the symptoms of vision loss, but are instead likely to pass this deformity onto their male offspring, who do suffer the repercussions of the disease [4].

The study was conducted on dogs, a species which shares many similarities in its eye structure with humans, and it was found that the disease was both preventable and curable [6]. This result was reached by replicating a working copy of the RPGR gene in humans. Afterwards, this gene was transported to the photoreceptors using a viral vector, which is a non-pathogenic virus that is unable to divide. In addition, to ensure the safety of this gene therapy, the healthy RPGR gene was attached to a ‘promoter’ which enabled the working gene to switch on and begin producing its proteins only when the virus had reached its destination [4]. After an injection was made below the retina of the dog with the viral vector, which was carrying both the promoter and the working RPGR gene, the researchers observed that the dog’s vision slowly began to restore. Therefore, this suggests that the working RPGR gene reached its destination and began producing photoreceptor ciliary proteins thus stopping the degeneration of photoreceptors in the retina.

Although the study is a step in the right direction, many future developments must first be made before the RPGR strand of X-linked Retinitis Pigmentosa can be deemed curable. The scientists responsible for the study suggest that the study should first be repeated over a longer period of time with more subjects [4]. Then the viral vector needs to be checked for safety for use on humans. Only then can a pharmaceutical version be made and the therapy progress to clinical trials. Therefore, it could be a while before an actual cure is produced. However, there is no doubt that this study has given hope to the many sufferers of this disease as well as  opening up the possibility of treating previously thought to be incurable eye diseases.

References:

1. Beltran, WA & et al 2012, ‘Gene therapy rescues photoreceptor blindness in dogs and paves the way for treating human X-linked retinitis pigmentosa’, Proceedings of the National Academy of Sciences of the United States of America, vol 109, no. 9,  pp. 2132-2137.
  
2. Bionic Vision Australia n.d., Retinitis Pigmentosa, viewed 17 March 2012, <http://www.bionicvision.org.au/eye/vision_impairment/rp>.

3. Dubuc, B 2002, Photoreceptors, viewed 18 March 2012, <http://thebrain.mcgill.ca/flash/d/d_02/d_02_m/d_02_m_vis/d_02_m_vis.html>.

4. University of Florida Health Science Center 2012, Researchers develop gene therapy that could correct a common form of blindness, viewed 14 March 2012, <http://esciencenews.com/articles/2012/01/23/researchers.develop.gene.therapy.could.correct.a.common.form.blindness>.

           5. University of Illinois 2011, Retinitis Pigmentosa, viewed 17 March 2012, <http://www.uic.edu/com/eye/LearningAboutVision/EyeFacts/RetinitisPigmentosa.shtml>.

           6. University of Pennsylvania 2012, Gene Therapy Research Team from Penn Vet and Scheie Eye Institute Cures Retinis Pigmentosa in Dogs, viewed 14 March 2012, <http://www.upenn.edu/pennnews/news/gene-therapy-research-team-penn-vet-and-scheie-eye-institute-cures-retinitis-pigmentosa-dogs>.

         7. National Eye Institude 2009, Damaged Rods and Cones, viewed 19 March 2012, <http://www.nei.nih.gov/eyeonnei/snapshot/archive/0909.asp>

1 comment:

  1. At present, there is no Retinitis Pigmentosa Treatment for long term to stop the movement of any retinal dystrophies. Natural treatment of Retinitis Pigmentosa with Herbal Remedies is useful to fight with this disease.

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