Gene therapy could help cure gradual blindness - study

It was thought the loss of light-sensitive cones and rods would cause irreversible blindness. Photo / 123RF

Scientists may one day be able to help thousands of people in Britain with an inherited condition that leads to the loss of sight, after partially curing blind mice and dogs.

The study found that congenitally blind mice and dogs with a condition similar to the condition retinitis pigmentosa could regain some vision following therapy based on the addition of a human gene that enabled cells in the retina to become sensitive to light.

Retinitis pigmentosa involves the progressive loss of both kinds of photoreceptors in the retina - the rods and the cones - usually from the edge to the centre, leading to worsening tunnel vision caused by the loss of peripheral sight.

However, in addition to rods and cones there are other cells in the retina - called the ganglion and the bipolar cells - that can remain undamaged. The researchers used gene therapy to convert these cells to light-sensitive photoreceptors by inserting an additional gene for a protein known as an "ion channel" which helps to convert light into a nerve impulse.

Once the scientists had converted millions of retinal cells by gene therapy, they injected another chemical known as a "photoswitch" into the eye, which attached itself to the ion channel protein, enabling the full conversion of light into an electrical signal relayed to the brain.

It was thought the loss of light-sensitive cones and rods would cause irreversible blindness but the new approach suggests that it may be possible to convert the remaining healthy cells into working photo-sensitive cells.

Blind mice that underwent the treatment were able to navigate themselves around a maze that they had been unable to cross before the gene therapy, according to the study, published in the journal Proceedings of the National Academy of Sciences.

In addition, both the mice and a group of dogs with inherited blindness were able to distinguish between flashing and non-flashing light, the scientists said.

The blind dogs had inherited a genetic disease caused by the same gene defects as some of the human patients with retinitis pigmentosa. They were rescued from an animal breeding centre and are undergoing tests to see how much of their vision has been restored, the researchers said.

"We've shown we can deliver the photoswitch and restore light response to the blind retina of dogs as well as in the mouse, and that the treatment has the same speed of response," said Professor Ehud Isacoff of the University of California, Berkeley.

- Independent