Gene therapy's 'temporary benefits' for retina disease
Two trials of gene therapy on an inherited form of blindness in children have shown some patients' eyesight can be improved - but only temporarily.
Gene therapy injections increased the retina's light sensitivity, showing potential for the treatment.
Children with Leber's congenital amaurosis (LCA) lack night vision and lose daylight vision.
Scientists from the UK and the US published their study results in the New England Journal of Medicine.
Leber's congenital amaurosis affects the functioning of the retina, the light-sensitive tissue at the back of the eye.
About 10% of people with LCA carry a mutated form of the gene RPE65 which is normally essential for vision.
But in people with LCA, the light-detecting cells eventually die and disrupt communication between the retina and the brain, leading to loss of vision.
Researchers at University College London's Institute of Ophthalmology and Moorfields Eye Hospital studied the effects of injecting healthy genes into the retinas of 12 young patients over six years.
They found that although half of patients experienced some improvements in their night vision, this peaked at six to 12 months after the treatment.
Also, their daytime vision did not appear to improve.
Prof Robin Ali, head of genetics at UCL's Institute of Ophthalmology, said: "Gene therapy improves night vision but there is no evidence that it slows progression of the disorder.
"We now need a more potent gene therapy vector."
He said the research team had developed a new, more powerful way of carrying and delivering the gene to its target cells.
The team is aiming to test the new vector soon in a second clinical trial funded by the Medical Research Council.
Another smaller trial, led by scientists from the University of Pennsylvania, found a similar pattern of improving eyesight in some patients lasting between one to three years after treatment with gene therapy.
Dr Samuel Jacobson, from the University of Pennsylvania's Scheie Eye Institute, in Philadelphia, said the trial results were important, even though the therapy doesn't appear to be a permanent treatment.
"The gain in knowledge about the time course of efficacy is an opportunity to improve the therapy so that the restored vision can be sustained for longer durations in patients."
He said the results highlighted the potential benefits of gene therapy as well as the problems still to be solved - for LCA and other diseases of the retina.