More Success With Gene Therapy for Blindness

Repeat treatment improves vision for three adults with rare eye disease

More Success With Gene Therapy for Blindness

WEDNESDAY, Feb. 8, 2012 (HealthDay News) -- As a child, Tami Morehouse had vision problems. She struggled to read the blackboard at school, and homework took hours.

Yet, she made it through high school and college, and became a social worker. Although she was never able to drive, she learned to ride a bike.

But in her 30s, with three young children, her vision took a turn for the worse. "I'd be reading a book and the words faded away," she said.

Morehouse was going blind, the result of Leber congenital amaurosis (LCA), a rare inherited eye disease that causes a progressive loss of vision. "As my kids needed me more and more, I was able to do less and less," Morehouse said.

That changed in 2009, when she was one of 12 people to undergo an experimental treatment using gene therapy in one eye. Now, scientists report even more progress, having successfully treated the second eye of three patients, including Morehouse. The new results are published Feb. 8 in Science Translational Medicine.

LCA is caused by a faulty gene, RPE65, that fails to produce an enzyme needed by the retina, the tissue in the back of the eye that converts light images into nerve signals that get sent to the brain.

Lack of the enzyme causes toxic byproducts to build up in the retinal cells, gradually killing them.

"It's inevitable and progressive, and people watch as they are losing more and more of their vision," said Dr. Jean Bennett, an ophthalmology professor at University of Pennsylvania Perelman School of Medicine and co-leader of the research team that pioneered the treatment. "By the time they're teenagers or young adults, they are severely impaired."

The treatment involved injecting a virus genetically engineered to carry a normal version of gene RPE65 into the retinal cells.

About two weeks later, with the eyes now producing the enzyme, the patients -- adults and children -- saw a marked improvement in their vision.

"They all gained vision in a very meaningful way," said Bennett, also a scientist at Children's Hospital of Philadelphia. "Children can read books, ride their bikes to their friends' houses -- things which they never could do before."

Initially, researchers only injected one eye because of safety concerns, Bennett explained. The fear was that the first injection would prime the immune system to recognize the virus and attack it when it was injected into the second eye. That would cause inflammation in the eye, potentially leading to more vision loss.

But animal studies showed that didn't happen, and so they decided it was safe to try the second eye in adults.

"It's amazing," Morehouse said. "I just feel so different. I used to wake up in the morning, so afraid and so anxious, that I would look over at the alarm clock and see nothing."

Prior to the treatments, she could see light and dark, but most of the world was hazy and gray. By night time, when her eyes were tired, she could see very little.

Today, her vision is still significantly impaired. She needs help finding her way to a table in a restaurant, for example, and reading isn't really possible. Yet, she can tell when someone is approaching, and she can make out a smile.

"Seeing my daughter walk across the basketball court. Seeing my son step up to the plate when he's playing ball -- it's phenomenal," Morehouse said.

Researchers verified that patients could see more by performing functional MRI scans before and after the second eye treatment. The brain imaging showed much more response to visual stimuli after their second eye was done.

At 47, Morehouse was the oldest patient. The prior study taught researchers that children improved the most, probably because their retinal cells had suffered less damage.

Now that researchers have established the procedure is safe in adults, they've started using gene therapy on the second eyes of children with the condition, Bennett said.

Though more research needs to be done and there are "technical" issues to be overcome, "we want to be able to use this approach in developing similar treatments for other more common blinding diseases," she said.

Dr. Richard Lewis, a clinical correspondent for the American Academy of Ophthalmology, called the results "exciting." Not only did the results show that treating the second eye is safe and effective, but that vision in the first eye also appears to improve as well.

"This is setting us up for the next step, which is to take the 5-year-old, the 8-year-old, or even the 6-month-old who has the mutation in this particular gene, and replace the enzyme using gene replacement therapy before permanent damage is done," said Lewis, who is a professor of ophthalmology at Baylor College of Medicine's Cullen Eye Institute in Houston.

More information

The Foundation Fighting Blindness has more on LCA.

SOURCES: Jean Bennett, Ph.D., M.D., F.M. Kirby professor of ophthalmology at Perelman School of Medicine, University of Pennsylvania, and Children's Hospital of Philadelphia; Richard Lewis, M.D., professor, ophthalmology, Baylor College of Medicine's Cullen Eye Institute, Houston; Feb. 8, 2012, Science Translational Medicine
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