Washington, May 4 (IANS): Gene therapy for leber congenital amaurosis (LCA), an inherited disorder that causes blindness starting in childhood, improves patients' eyesight and the retina's sensitivity within weeks of treatment, says a new study.

The areas of treated retina rapidly gained visual sensitivity, expanded and then contracted. The new studies focus on trial participants who routinely underwent extensive tests of their vision and imaging of the retina from baseline up to six years after the treatment.

"Gene therapy for LCA demonstrated, we could improve vision in previously untreatable and incurable retinal conditions," said Samuel G. Jacobson, who led the clinical trial at the University of Pennsylvania's Scheie Eye Institute, Philadelphia.

About 10 percent of people with LCA carry a mutated form of the gene RPE65, protein critical for vision. This gene makes a key protein found in the retinal pigment epithelium, a layer of cells that nourish the light sensors or photoreceptor cells of the retina.

For the trial, 15 people with LCA received retinal injections of a harmless virus engineered to carry healthy RPE65 genes.

This gene therapy relies on viral vectors as a means to deliver instructions for making the desired protein. In this case, the virus was designed to produce healthy RPE65.

"Within days of the injections, some patients reported increases in their ability to see dim lights they had never seen before. It was remarkable for us to get this feedback that things were indeed changing positively," Jacobson pointed out.

Four of the 15 patients started relying on an area of the retina near the gene therapy injection site for seeing letters.

"We've been able to positively alter and extend the visual life of patients with LCA, and we now have to develop workable strategies for extending it even further," Jacobson concluded.

The results appeared online in the New England Journal of Medicine