These improvements to vision have lasted at least four years, and it is hoped that the technique could be extended to other more common forms of inherited blindness.
'There have recently been questions about the long-term efficacy of gene therapy, but now we have unequivocal proof that the effects following a single injection of viral vector [carrying the genes] are sustained,' said Professor Robert MacLaren of Oxford University, who led the study.
His team treated six patients with choroideremia, which affects around 1 in 50,000 people. The condition is caused by a mutation of the CHM (Choroideremia (Rab Escort Protein 1)) gene, which results in progressive damage to light-responsive retinal cells. The team used a harmless virus to inject a properly functioning version of the CHM gene into the retina to try to stimulate the regeneration of cells and halt visual loss.
The study, which was published in the New England Journal of Medicine, found significant improvements in the vision of two out of the six patients treated, and these have lasted nearly four years. As the vision in their treated eye improved, their untreated eye showed continued deterioration. Three patients, who were less severely affected by the disorder, also displayed preserved vision over the same time period.
'To permanently restore sight to people with inherited blindness would be a remarkable medical achievement. This is the first time we've seen what appears to be a permanent change in vision after just one round of treatment,' said Dr Stephen Caddick of the Wellcome Trust, which partly funded the study.
Jonathan Wyatt, the first patient to be treated with the gene therapy, has maintained twice the level of vision in his treated eye. 'The left eye is much improved to such an extent that I use it mostly to get about these days… Without it I think I would be tapping with a white stick.'
If the next round of clinical trials is successful, gene therapy for choroideremia could be available within the next three years, and the technique could be extended to other inherited forms of blindness, such as retinitis pigmentosa and genetic-related macular degeneration. Although these disorders have a more complex genetic basis than choroideremia, Professor MacLaren is already preparing for clinical trials as early as next year, with the potential for treatments in the next five to ten years.
'As we learn more about genetics we realise that correcting faulty genes even before a disease starts may be the most effective treatment. This is the breakthrough we have all been waiting for,' said Professor MacLaren.
Chief executive of the UK charity RP Fighting Blindness, Tina Houlihan, commented: 'Advances made in genetic therapies are extremely encouraging for people living with inherited eye conditions. We look forward to even greater steps forward being made in the future as treatments are refined ever further.'