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Gene Therapy a Step Closer to Restoring Eyesight to Some Blind Patients

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Researchers have moved a step closer toward fully restoring the eyesight of people with a rare genetic disorder.  A new study shows the treatment is safe and effective, and could pave the way for helping cure more common causes of blindness.

Leber's congenital amaurosis is an extremely rare condition that causes blindness in approximately 4,000 people in the United States.  

Approximately five to seven babies are born each year with the progressive inherited disorder, according to Jean Bennett, a professor of ophthalmology at the University of Pennsylvania in Philadelphia. "It's probably one of the most severe forms of retinal degeneration, most severe because it affects infants, and it's usually the parents who first notice that their children aren't seeing the way most normal children do at approximately six weeks of age," Bennett said.

LCA is caused by a single defective gene. This defect prevents normal function of the retina, the light-sensitive layer of cells at the back of the eye. This results in severely impaired vision from a very young age and there are currently no effective treatments available.

A recent study done on animals has shown that tests on both eyes are safe and effective and improve vision. This clears the hurdle for trials in humans to receive treatments in both eyes.

In a groundbreaking clinical trial last year, researchers repaired the gene and injected it into the retinas of the single eye of 12 people, where it started to produce healthy cells.  Bennett says the patients experienced a dramatic improvement in their eyesight in the single eye, particularly among younger patients whose vision had not deteriorated to near blindness. "It now allows them to be able to read books and sit in the front of a classroom and see what a teacher is writing on a blackboard and to riding their bike around the neighborhood by themselves, whereas before they enrolled in the study, they were learning braille. They sat in the back of a classroom looking at computer monitors which magnified the teacher's image and they were dependent upon canes or holding on to people to walk around," Bennett said.

Bennett, one of the researchers, says the study participants have been clamoring to have their other eye treated with the gene therapy.  But before researchers did that, they wanted to make sure the treatment was safe.

Now researchers are waiting for the green light to treat the second eye of Leber's congenital amaurosis patients, to significantly restore their sight in both eyes.

Bennett says a similar strategy could someday be used to treat age-related macular degeneration, which is responsible for vision loss in more than 14 million older adults worldwide each year.  The disease is the result of damage to the macula, a part of the retina in the eye,  which results in central vision loss.

Scientists have identified several gene candidates involved in the disease.

Although there are currently no gene therapy trials under way to treat macular degeneration, Bennett says her study shows that using a virus to repair defective genes involved in the disease is safe. "If a strategy is developed to deliver a corrective gene to the eyes of patients with AMD, it may be possible to correct the defect in the second eye of the person at a later time point," she said.

An article on gene therapy by the University of Pennsylvania's Jean Bennett and colleagues is published this week in the journal Science Translational Medicine.

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