Gene therapy restores significant vision in congenital blindness

US doctors have used gene therapy to restore significant vision in 12 patients who were previously blinded by a disease called Leber's congenital amaurosis. The study, conducted by researchers at the Children's Hospital of Philadelphia and the University of Pennsylvania School of Medicine, was published online in the Lancet on 24 October.

Leber's congenital amaurosis is a hereditary condition characterised by degeneration of the retina and loss of vision in the first few months of life. The disease affects one in 80,000 people and is caused by mutations in one of 13 different genes. All the study participants had a defective RPE65 gene, which codes for an enzyme that makes a vitamin A derivative that is essential for detecting light.

The researchers injected the patient's worst eye with normal copies of the gene inserted into an adenovirus vector- these are harmless viruses which help deliver the functional gene to the affected cells. Last year the team reported success of the treatment in four adult patients. They went on to treat a further nine patients, including five children. The results were most pronounced in four children aged 8-11. The children 'are now able to walk and play just like any normally sighted child', Dr Albert Maguire said, one of the lead authors of the study.

'These results are outstanding. We are delighted by not only the restoration of vision and the vision improvement that has been sustained, but also that the treatment has demonstrated an outstanding safety profile,' says Dr Stephen Rose, chief research officer of Foundation Fighting Blindness, which significantly funded the study.

Though vision has not been restored to normal, day to day tasks that previously severely restricted independency has now become possible: such as navigating around obstacles in dim lighting. The treatment is limited because damage has already occurred to the eye and only one eye was treated.

'The big elephant in the room is: Can you treat the other eye?' Rose said. The foundation will now fund research 'to make sure that if you go back and treat the other eye, it won't ablate the positive results in the first eye due to an immune reaction or something else'.

Further work will also involve optimising the dosage of the adenovirus used to carry the gene into the eye. There are also hopes that by using different genes, the scientists will be able to translate the results to other conditions causing blindness such as macular degeneration.

Dr Jean Bennett, Kirby professor of Ophthalmology at the University of Pennsylvania School of Medicine, said: 'The clinical benefits have persisted for nearly two years since the first subjects were treated with injections of therapeutic genes into their retinas. These remarkable results have laid a foundation for applying gene therapy not only to other forms of childhood-onset retinal disease, but also to more common retinal degenerations'.