Gene therapy partially restores sight in mice and dogs

Scientists have used gene therapy to restore some sight to animals with visual impairment similar to retinitis pigmentosa, a type of human blindness. The findings relate to restored light sensitivity, but may hold promise for restoring vision in the future.

Retinitis pigmentosa is a genetic disorder affecting approximately 1 in 4,000 people, in which retinal light-sensing cells degenerate, resulting in tunnel vision and eventually total sight loss.

Researchers at UC Berkeley, USA, performed experiments on mice with blindness caused by a genetic defect similar to retinitis pigmentosa. By inserting a gene followed by an injection of a chemical 'photoswitch', the authors of this study were able to genetically engineer nerve cells in mouse retinas at the back of the eye to become light-sensitive. Mice treated in this way were able to navigate a water maze like sighted mice.

The nerve cells targeted by the gene therapy, retinal ganglion cells, are not normally responsive to light, but are connected to the underlying nerves that relay visual information to the brain, and which remain functional in retinitis pigmentosa.

Following the success of experiments in mice, the researchers moved on to test the treatment in dogs with a genetic form of blindness.

'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', said lead researcher Ehud Isacoff, professor of molecular and cell biology at UC Berkeley.

Early experiments showed that the treated dog retinas responded to light in a similar way to the mouse retinas, although no experiments were conducted to establish if the dogs could see again, explains NHS Choices.

'Use of such a clinically relevant large animal model allows us to begin tackling the next challenges on the road to translating this novel therapeutic strategy to human patients', said William Beltran, an author on the paper and associate professor of ophthalmology at the UPenn School of Veterinary Medicine.

If this therapy could be shown to work in people, it could help patients with forms of blindness where there is degeneration of light-sensitive cells but the underlying nerve cells remain intact, such as retinitis pigmentosa. However, patients with blindness due to other causes, such as age-related macular degeneration, would not be candidates for treatment.