A new gene therapy method can offer cure for the blind. Retinitis pigmentosa is a common form of blindness. This hereditary retinal blindness is caused by mutations in genes expressed in photoreceptors.
When University of Florida researchers replaced a malfunctioning gene in the eye with a normal working copy, vision was restored significantly. Their findings were published in the Proceedings of the National Academy of Sciences online on January 23, 2012.
About 100,000 people in the United States have X-linked retinitis pigmentosa. This common form of blindness is caused by a genetic defect which is passed from mothers to sons. Girls carry the trait, but boys end up losing their sight.
Affected children are usually born with normal vision and they gradually lose their vision. They usually go blind in the second decade of life.
Vision loss is caused by degeneration of photoreceptor cells, the light-sensitive cells in the eyes.
Gene therapy in mouse and dog models of a primary retinal pigment epithelium disease has already been done. Human clinical trials are showing encouraging results.
However, gene therapy for the common primary photoreceptor blindness has not been done. This study can have a big impact because it can treat a form of blindness that affects a lot of people.
What the team of scientists did:
Using a replication-defective recombinant adeno-associated virus as a vector, they delivered the retinitis pigmentosa GTPase regulator (RPGR) gene, which encodes a photoreceptor ciliary protein, by subretinal injection.
Imaging showed rescue of the damaged photoreceptor cells after subretinal injections.
Additional tests also showed that both rod and cone photoreceptor function were greater in treated eyes compared to untreated eyes. Normal photoreceptor structure and reversal of opsin mislocalization in treated areas expressing human RPGR protein in rods and cones were observed.
Results from the experiments were encouraging. Rescue of the damaged photoreceptor cells worked. Gene therapy cured photoreceptor blindness in dogs.
Safe and effective gene therapy in animal models of X-linked retinitis pigmentosa can pave the way for applying the treatment to human patients.
According to research co-author William W. Hauswirth, "providing the gene that's missing is one of the ultimate ways of treating disease and restoring significant visual function."
Improving the sight of people who can't see or can barely see can change their lives significantly.
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