New Therapy Holds Promise for Restoring Vision
Retinitis pigmentosa, a condition afflicting people of all ages, causes a gradual loss of vision. Sight is lost from the periphery to the center, usually leaving people with the inability to navigate their surroundings. Some 100,000 Americans suffer from this group of inherited retinal diseases. Now a new genetic therapy that employs a virus to insert a gene for a common ion channel into normally blind cells of the retina that survive after the light-responsive rod and cone photoreceptor cells die may hold hope for restoring vision, according to research led by the University of California, Berkeley and published early online in December 2014 in the journal Proceedings of the National Academy of Sciences.
A release from the university explains that the researchers attached photoswitches — chemicals that change shape when hit with light — to the channels in the eye to make them open in response to light, thus activating the retinal cells and restoring light sensitivity.
The scientists who invented the photo switch therapy and veterinary colleagues at the School of Veterinary Medicine of the University of Pennsylvania (UPenn) report that congenitally blind mice regained the ability to navigate a water maze as well as normal mice.
The treatment worked equally well to restore light responses to congenitally blind mice and dogs, indicating that it will be feasible to restore some light sensitivity in blind humans.
The release quotes lead researcher Ehud Isacoff, professor of molecular and cell biology at UC Berkeley, as saying, “The dog has a retina very similar to ours, much more so than mice, so when you want to bring a visual therapy to the clinic, you want to first show that it works in a large animal model of the disease. We’ve now showed that we can deliver the photoswitch and restore light response to the blind retina in the dog as well as in the mouse, and that the treatment has the same sensitivity and speed of response. We can reanimate the dog retina.”
Advantages over other gene therapies
The therapy has several advantages over other sight restoration therapies now under investigation, says vision scientist John Flannery, UC Berkeley professor of vision science and of molecular and cell biology. It uses a virus already approved by the Food & Drug Administration for other genetic therapies in the eye; it delivers an ion channel gene similar to one normally found in humans, unlike others that employ genes from other species; and it can easily be reversed or adjusted by supplying new chemical photoswitches. Dogs with the retinal degeneration provide a key test of the new therapy.
“Our ability to test vision is very, very limited in mice because, even in the healthy state, they are not very visual animals, their behaviors are largely driven by their other senses,” he says. “Dogs have a very sophisticated visual system, and are being used already for testing ophthalmic gene therapy.”