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What is Retinitis Pigmentosa?
Retinitis Pigmentosa (RP) is a set of hereditary retinal diseases demonstrating clinical features similar to LCA and characterized by degeneration or rod and cone photoreceptors. By current epidemiological estimates, there at least 300,000 patients with RP worldwide, of which less than 3% carry the inherited deficiencies of either RPE65 or LRAT.
What causes RP?
To date, 36 gene defects have been found to cause RP. Two of these gene defects are of interest to QLT: those due to defects in retinal pigment epithelial protein 65 (RPE65) and lecithin-retinoid acyltransferase (LRAT) genes, which are part of a biochemical pathway called the visual cycle. The visual cycle is responsible for supplying the rod and cone cells of the retina with a chemical 11-cis-retinal. When these genes are defective 11-cis-retinal is not produced at adequate levels. Without 11-cis-retinal, the rods and cones cannot sense light, and this results in vision loss.
What are the current treatments for RP?
Current treatment of RP is supportive and includes periodic ophthalmic evaluation. Treatments under investigation include gene therapy, neuroprotection, and retinal implants. QLT is investigating a synthetic retinoid replacement, QLT091001, as a potential treatment for RP.
The retinas in patients with RP still have relatively normal appearance, both on physical and histological examination, even though they lack normal function. There may, therefore, be a potential to use a treatment intervention to stop the degeneration before much of the permanent damage takes place.
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