Oct. 24 (HealthDay News) -- Gene therapy can improve the vision of people with a severe form of genetically inherited retinal degeneration called Leber congenital amaurosis (LCA), a new study shows.

People with LCA, which is caused by mutations in any of least 13 genes, have severe vision loss and abnormal eye movements in early infancy and during early childhood. Most people with the disease are blind by their 30s or 40s. There is no cure, according to background information provided in a news release.

The new phase I trial included 12 patients, aged 8 to 44 years, who were injected in one eye with genetic material meant to correct LCA. The gene therapy led to at least a 100-fold increase in pupillary light response (constriction of the pupil when it's exposed to light) in the participants. An 8-year-old patient developed nearly the same level of light sensitivity as a person with normal vision, the study authors reported.

In general, the greatest improvements were seen in children aged 8 to 11, all of whom gained ambulatory vision -- being able to see well enough to walk unaided.

"All 12 patients given gene therapy in one eye showed improvement in retinal function. The effect was stable during follow-up. The results support our hypothesis that the response to subretinal gene therapy depends on the extent of retinal degeneration and, therefore, the age of the patient," wrote Dr. Jean Bennett, of the University of Pennsylvania School of Medicine in Philadelphia, and colleagues.

"The most noteworthy result was the ability of children to navigate an obstacle course independently and accurately, even in dim light," the study authors wrote. "The visual recovery noted in the children confirms the hypothesis that efficacy will be improved if treatment is applied before retinal degeneration has progressed. Assessment of whether the treatment alters the natural progression of the retinal degeneration will be possible in follow-up studies," they added.

"The success of this gene therapy study in children provides the foundation for gene therapy approaches to the treatment of other forms of LCA and of additional early onset retinal diseases," the researchers concluded.

The study is published in the Oct. 24 online edition and in an upcoming print issue of The Lancet.

SOURCE: The Lancet, news release, Oct. 24, 2009