A temporary benefit to night vision

Final results from the first clinical trial of gene therapy for Leber congenital amaurosis (LCA) show that the benefits are temporary. Although the therapy can improve night vision it does not stop LCA from progressing.

LCA is a family of rare inherited retinal conditions. Faults in any of several genes can lead to a pattern of sight loss that starts with losing night vision in childhood and progresses to losing detailed, day vision over time.

In the current study, researchers targeted the gene RPE65. This gene is important for nourishing the light-sensitive cells in the retina that deal with night vision and peripheral vision. Without RPE65 these cells die and sight loss is present from birth.

The research was carried out at University College London's Institute of Ophthalmology and Moorfields Eye Hospital and was part-funded by Fight for Sight.

12 participants, aged 6-23, were given eye injections of a ‘viral vector’ – a virus (rAAV2/2) engineered to be harmless and to carry a healthy version of RPE65. Injections were given to the worst eye only so that the effect could be compared to the untreated eye. Four participants were given a lower dose and eight a higher dose.

Early results from the study were published in 2008. These showed that 1 of the first 3 participants reported better night vision soon after treatment.

Final results from all 12 participants show that half had some improvement to night vision for up to 3 years. The improvement was best 6-12 months after treatment and then reduced. However the effect was strong enough to be picked up by a test that records electrical activity from cells in the retina and day vision did not improve.

It works in principal

Dr Dolores M Conroy, Director of Research at Fight for Sight, said:

“While the early results from this study seemed very promising it’s now clear that we have quite a way to go. Gene therapy using rAAV2/2 can bring modest benefits that last up to three years, but the effects vary from person to person and the retina continues to lose cells.

“In principal, it can work. So what we need now is continued research to develop a better version of the therapy that gives a bigger increase in healthy RPE65 activity. The aim is still both to improve vision and to protect the retina.

“The team has now developed a new, more potent viral vector that produces higher levels of RPE65. This will be tested in a new second clinical funded by the Medical Research Council.”

The results were published in the New England Journal of Medicine. Results from a similar trial in the USA confirm the current findings.