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Treating Two Eyes Safe and Effective, New Study Confirms
By Salynn Boyles
WebMD Health News
Reviewed by Laura J. Martin, MD
Feb. 8, 2012 -- Functionally blind for many years, Tami Morehouse calls the gene therapy that partially restored her sight nothing short of a miracle.
Morehouse was the first of 12 patients with a rare congenital retinal disease to receive the experimental treatment in one eye three years ago, and she is one of just three who has now had the gene therapy in both eyes.
The 47-year-old Ohio social worker and mother of three says before having the treatment she worried everyday that she would lose what little sight she had left.
"This treatment literally gave me a much brighter future," she says. "My world just lit up and I saw things much more clearly. Soon after the second treatment I went out to dinner with my husband and I looked down and thought, 'Oh my gosh, I can see the glass sitting in front of me.'"
Gene Therapy Targets Eye Mutation
The study Morehouse took part in was among the first to show that gene therapy can improve vision in people with inherited blindness.
The updated findings prove that treating both eyes is safe and beneficial, says researcher Jean Bennett, MD, PhD, of the University of Pennsylvania.
Patients received injections of healthy copies of a dysfunctional gene into their eyes in an effort to get the cells to work better.
The injections worked so well that Bennett and colleagues plan to treat the second eyes of the remaining five children and four adults who took part in the original study.
"There was some concern that the first injection would set up an immune response, causing the body to reject the second injection," Bennett says. "If that happened, the benefits to the first [treated] eye could be threatened."
But that is not what happened.
After having the injections in their second eye, the three patients were better able to see in dim light, and two of the three were able to navigate obstacles in low-light situations.
Half of Patients No Longer Legally Blind
All of the patients had an inherited, degenerative retinal disease called Leber congenital amaurosis (LCA), which is caused by a mutation in the RPE65 gene and generally progresses to blindness by mid-adulthood.
Morehouse says her vision became worse with each of her three pregnancies.
By the time she reached her early 40s, she saw little light or color, and most objects looked like "dark, hazy, blurry blobs," she says.
The treatment involved injections of a genetically engineered virus that carried a normal version of the RPE65 gene.
After the first injections, the vision of six of the 12 study participants improved to the point that they were no longer classified as legally blind.
"One of the children who took part in the original study was riding a bicycle within a year," says study co-author Manzar Ashtari, PhD, of the Children's Hospital of Philadelphia. "This is a child who used a cane and held on to adults to guide him before having the treatment."
Gene Therapy Might Prevent Blindness
The hope is that similar therapies targeting other mutations can be used to treat a large number of inherited diseases that cause blindness.
Katherine A. High, MD, of Children's Hospital of Philadelphia, who also worked on the study, says there are now 200 known genetic mutations that cause vision loss.
Because LCA is a degenerative disease, there is also hope that the treatment may one day be used in very young children, or even babies, before vision loss has occurred.
"For many genetic diseases -- not just this one -- early intervention will hold the key to optimal outcomes," High says.
Morehouse is most excited by this promise.
"If this treatment or treatments like this one can keep children from losing their vision in the first place and spare them the struggles that I had growing up, that is truly a miracle," she says.
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