Gene therapy has enabled dogs born blind because of an inherited disorder to have some of their sight restored. This is the first time that gene therapy of this type has proved to be successful in a large animal. The achievement might mean that the technique could be adapted to help the small number of children born with a similar disorder.

The human condition, called Leber congenital amaurosis, results in children being born nearly blind or with severely reduced vision. The condition is caused by a defect in the gene RPE65, which is vital in helping to correctly construct photo-receptors in the eye which convert light into nerve signals read by the brain. When the gene is defective, the retina gradually degrades. The condition is currently untreatable.

The researchers, from the University of Pennsylvania, took cells from the retina of dogs with the equivalent genetic disorder. These were then 'infected', using a non-infectious carrier virus, with a correct copy of the RPE65 gene. Because viruses reproduce by incorporating their own genes into the structure of the cells surrounding them, the gene entered the retinal cells.

The 'infected' retinal cells were then injected back into the eyes of the dogs, who were then tested to see how they performed. The eyes were found to start to respond to light and dark stimuli as healthy eyes do. The dogs also were able to avoid obstacles when tested in dim light.