Published August 12, 2009
Scientists believe the brain of a blind woman rewired itself and enabled her to see after partial vision was restored to sections of her retina through gene therapy.
The finding surprised scientists at the University of Florida College of Medicine and the University of Pennsylvania who two years ago began testing the safety of gene therapy in three patients born with Leber congenital amaurosis type 2, a rare blindness condition. The findings are contained in a study to be published Thursday in the New England Journal of Medicine.
“This was phase 1 of a National Eye Institute study and we wanted to measure whether gene therapy was safe for the eye and safe for the body,” said Dr. Artur Cideciyan, a research associate professor at the University of Pennsylvania. “We were hopeful that something positive would end up occurring as well.”
Scientists found that within weeks of adding healthy genes to the retinas of study participants (a woman and two men between the ages of 21 and 24), the three began to experience significant improvements, including improved sensitivity to light.
“We found that the improvements occurred only in the treated eyes and in the regions that were injected with the new genes,” Cideciyan said. “We also found that the improvements and the safety were maintained for 12 months after the initial injection.”
The tiny portions of the patients’ retinas that received gene therapy experienced restored function up to 1,000-fold during the day and 63,000-fold at night.
But it was the woman in particular who surprised researchers when she announced that a year after receiving treatment, her vision continued to make small improvements. She said she could read the digital clock in her parents’ car – something she had never done before.
“That prompted us to measure where her gaze was fixed while looking at a variety of dim targets,” said Dr. William W. Hauswirth, a professor in the ophthalmology department at the UF College of Medicine, who led the study. “This showed she now has two preferred centers of vision rather than one, depending on the brightness of the object.”
Cideciyan said healthy adults have a single preferred center of vision that they use to see objects. Based on their findings, researchers hypothesize that the female patient’s brain rewired itself to use two preferred centers, which it shifts back and forth between depending on the situation.
“I think that it is a very intriguing hypothesis … that she learned to use an area of her retina that was improved through gene therapy,” said Dr. Brian Brooks, an investigator with the National Institute of Health’s National Eye Institute.
“We don’t yet understand the precise mechanism that occurred to make this happen,” said Brooks, who did not participate in the NEI-supported study. “But the hope is that we will be able to use the finding to cold train patients to use new areas of their retinas that they’re not accustomed to using.”
The finding could also prove beneficial to others with degenerative retinal conditions similar to Leber congenital amaurosis, which is a leading cause of blindness in infants and children, Cideciyan and Brooks said.
Cideciyan said the safety trial will continue for the next three years and the participants will be followed for 15 years, as mandated by the U.S. Food and Drug Administration. The study also will be expanded to include other age groups and participants.