Disappointing results from gene therapy trials for blindness

5 May 2015

Two trials to test the safety and efficacy of gene therapy for an inherited form of blindness have shown only temporary improvements in vision.

Leber’s congenital amaurosis (LCA) is a group of progressive, degenerative forms of eye disease caused by mutations in at least 19 different genes; it causes loss of night vision, with progressive loss of daytime vision. In some patients it is caused by mutations in the RPE65 gene, which disrupt normal retinal function.

Early trials of a new form of gene therapy for the condition to deliver healthy RPE65 genes showed promising results with improvements in vision, but the latest results published in the New England Journal of Medicine have proved disappointing.

Half of the twelve trial patients at the University College London's Institute of Ophthalmology and Moorfields Eye Hospital, who were followed over six years, experienced initial improvements in their night vision over up to three years, with the greatest improvements observed between six and twelve months following treatment. However, these improvements did not persist, and none were observed for daylight vision. Three patients experienced inflammation of the eye and two showed ‘clinically significant deterioration’ of vision.

However, trial researcher and Head of Genetics at the Institute of Ophthalmology Prof Robin Ali commented: "We now need a more potent gene therapy vector"; one is reportedly already in development.

An even smaller US trial at the University of Pennsylvania's Scheie Eye Institute had similar results, reported in the same journal. Researcher Dr Samuel Jacobson said that findings would help develop improved, longer-lasting gene therapeutics and better ways of using them to achieve optimal benefits for patients – for example, repeated treatment, combination of gene therapy with medication, or individually targeted administration of gene therapy to the most suitable parts of the retina.

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