PHILADELPHIA – One year after a trio of young adults received gene therapy for an inherited form of blindness, researchers have documented that the patients are still experiencing the same level of remarkable vision improvements previously measured within weeks. This is the first study to report one-year gene therapy safety and efficacy results in treating young adults with Leber Congenital Amaurosis (LCA), a hereditary condition that causes severe vision impairment in infants and children. The findings are published in Human Gene Therapy, now online, and in the New England Journal of Medicine (NEJM) this week.

The three patients – 22, 24 and 25 years old – who received the gene therapy have a specific type of LCA caused by a genetic mutation in the RPE65 gene. This gene normally makes a critical protein in the visual cycle. Without this RPE65 protein, light-sensitive photoreceptor cells are starved of a retina-specific form of vitamin A and cannot function, blocking vision.

To correct this genetic defect, researchers targeted retinal regions with impaired, but intact, photoreceptors and injected healthy copies of the RPE65 gene under the retina. One year after the single injection, the healthy genes continue to make this critical protein, increasing the retina’s sensitivity to light.

“We had previously shown that RPE65 gene therapy can completely reverse one of the two components of this complex disease and provide patients with increased day- and night-vision within weeks,” said Artur V. Cideciyan, PhD, Research Associate Professor of Ophthalmology at the University of Pennsylvania School of Medicine and lead author of the publications. “We now show that the longevity of the visual improvements extends to at least one year.”

The team of researchers from the University of Pennsylvania School of Medicine included Tomas S. Aleman, MD, Research Assistant Professor of Ophthalmology and Samuel G. Jacobson, MD, PhD, Professor of Ophthalmology at Penn Medicine’s Scheie Eye Institute and principal investigator of the clinical trial, along with additional colleagues at Penn and at the University of Florida, Gainesville.

One patient was able to read an illuminated clock for the first time, as reported in the NEJM article, one year after the treatment. This new ability was not caused by a further increase in light sensitivity, which remained unchanged from 1 to 12 months after the treatment, but likely by a slow change in the direction of focus to her treated retina. The change appeared 12 months after gene therapy, but not before.

“This fascinating finding shows that a person can adapt to the new vision resulting from gene therapy over a prolonged period of time,” said Jacobson. “We will look closely at whether these slow visual gains could be accelerated with visual training in future studies.”

As further reports of the safety and efficacy of ocular gene therapy in hereditary blindness come forth, treatment strategies in subsequent phases of the clinical trials can be refined.

This Phase I clinical trial is supported by the National Eye Institute (NEI) at the National Institutes of Health. For additional information about LCA, visit www.nei.nih.gov/lca. To view the NIH press release, visit http://www.nih.gov/news/health/aug2009/nei-12.htm. Find more information about this trial (NCT 00481546) at www.clinicaltrials.gov.