Gene therapy reverses ‘untreatable’ sight loss in young men

British scientists have developed a new therapy which improves the vision of people with a rare genetic disorder called choroideremia.

Similar methods could be used to treat more common forms of blindness in the future, according to the authors of the study, which has been published in the New England Journal of Medicine.

The condition, which only affects young men, is caused by a faulty gene that kills light-detecting cells in the back of the eyes. The therapy involves injecting working copies of the gene into the eyes, which allow the faulty cells to regenerate.

Early clinical trials, carried out over the last four years on 32 patients, have demonstrated that the change is ‘long-lasting’, and therefore suitable to be offered as a treatment.

Choroideremia is estimated to affect one in 50,000 people. Those with the condition generally notice a gradual loss of peripheral vision, leading to ‘tunnel vision’ and eventually complete loss of their sight. The condition was previously considered untreatable.

The new therapy has been shown to not only halt the progress of the disease, but in some cases improve the patients’ vision.

Robert MacLaren, the Oxford University eye surgeon leading the trial, told the BBC: ‘The concept of gene therapy is that it corrects gene defects. Ideally, we should only have to do that once, because once the DNA is corrected and inserted into the correct cell, that cell should be able to continue its function as normal.

‘We seem to have achieved this concept of one single treatment that does not need to be repeated which is unlike traditional medicines.’

The professor says that he anticipates a gene therapy for choroideremia being licensed within three years.

Instant analysis
Vision is a complex neurological process, involving the falling of light on the retina, transmission of nerve impulses to the brain, the integration of the information received, then reverse signals to the muscles of the eye to allow the focusing of the lens and the movement of the eye itself. And that is the simplified version of the story.

An injury or lesion anywhere along this pathway can render a person impaired of sight or blind. A perfectly healthy person can suffer a stroke that affects the visual centres of the brain, leaving the retina and optic nerves intact; conversely, a patient may have a degenerative eye disorder that robs them of their sight via breakdown of the retina, again leaving the rest of the system unimpaired. An otherwise heathy individual may suffer from an unexpected cataract or glaucoma and be rendered visually impaired.

We cannot, therefore, say the cure for blindness is nigh. This new finding applies only to a subset of people who are blind.

There have been many promising advances in the treatment of developing or established blindness. We are taking small steps closer to the day when all those who are blind or visually impaired will have the chance to receive definitive treatment.