Gene therapy could help blind people see again

Washington, Oct 17 : Researchers relied on gene therapy to restore vision to mice which suffered from degeneration of the light-sensing retinal rods and cones, a common cause of human blindness, because of lack of protein.
"This is a proof of principle that someday we may be able to repair blindness in people with conditions like retinitis pigmentosa and macular degeneration," said Richard Masland, director of Cellular Neurobiology Lab at the Massachusetts General Hospital (MGH).

"There are several limitations we need to overcome before we can begin clinical trials, but I'm optimistic that this work may someday make a big difference for people who otherwise would have no vision at all."

The study was designed to investigate the effect of light-sensitive protein melanopsin in retinal ganglion cells of the eye. These specialised neurons receive light signals from the rods and cones and convey them to the brain via the optic nerve.

Melanopsin is usually produced in a set of cells involved with establishing circadian rhythms but not with vision.

The MGH team used the standard viral vector to deliver the gene encoding melanopsin throughout the retinas of mice whose rod and cone receptors had degenerated from lack of a crucial protein.

Four weeks after delivery of the gene, melanopsin - normally produced in one percent of retinal ganglion cells - was found in about 10 percent of ganglion cells in the treated eyes but not in eyes that received a sham injection, according to a MGH press release. Examination of the melanopsin - expressing cells revealed that all responded to light, although the neuronal signal was delayed and persisted after the light signal had stopped, which is typical for a melanopsin - mediated signal.

Two behavioural tests verified that the treated mice - which otherwise would have been essentially blind - had enough vision to find a darkened refuge in an otherwise brightly - lit area and to successfully learn that a light indicated a safe platform to which they could swim.

"The same level of melanopsin expression in a human retina might allow someone who otherwise would be totally blind to read newspaper headlines, but the slowness of the response would be a problem," Masland said.

These findings were published in Tuesday's edition of the Proceedings of the National Academy of Sciences.