Gene therapy is emerging as a promising tool in the fight against blindness in children and adults.
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Normally, cells in the retina at the back of your eyes sense and translate light rays into electrical signals. These travel your optic nerve to the brain, where they are processed into the images you see.
When gene mutations cause deterioration in the retina, as seen in hereditary retinal diseases like Leber congenital amaurosis (LCA) and Stargardt disease, eye experts can provide corrective lenses, low vision aids and related care.
However, the underlying genetic defect, which makes the cells unable to function well and eventually die, leads to progressive vision loss and eventual blindness.
“Research now underway promises a brighter future for these patients,” says Elias I. Traboulsi, MD, MEd. “We will see significant advances in gene transfer therapy, stem cell therapies and drug therapies for hereditary retinal diseases in the coming decades.”
To prepare for these emerging therapies, Cleveland Clinic eye experts work with genetic counselors and low vision specialists to assess, treat and actively track patients’ retinal diseases over time.
How gene therapy works
Patients with hereditary retinal diseases have a gene that does not work properly. In gene therapy, a normally functioning retinal gene is inserted into a vector (usually a weakened virus). The vector is injected in or near the patient’s retina in hopes of delivering a working copy of the gene to the patient’s retinal cells.
Research on this technique has begun. Its effects on retinal function and vision in patients with hereditary retinal diseases, including LCA, Stargardt disease and others are being discovered and will emerge over the next few years.
Before participating in a clinical trial of gene therapy, patients must have genetic testing to get a precise molecular diagnosis. “Advances in genetic testing and the availability of commercial tests at certified laboratories have made this easier,” says Dr. Traboulsi.
To help families understand what the results mean, genetic counseling always accompanies genetic testing.
Tracking diseases over time
The effects of mutations in genes controlling vision are complicated. Sometimes different mutations in one gene can cause slower or faster visual decline and lead to the diagnosis of different clinical disorders.
For instance, mutations in RPE65 can cause LCA in childhood or retinitis pigmentosa in adulthood. The same is true for ABCA4 mutations, which can cause Stargardt disease or cone-rod dystrophy.
Studies underway use new imaging technology as well as traditional visual acuity and visual field measurements to compare the speed of retinal degeneration in treated and untreated patients.
“For example, we are participating in ProgStar, a study sponsored by Foundation Fighting Blindness, to learn more about the progression of patients with untreated Stargardt disease,” says Dr. Traboulsi.
“Understanding the natural history of the disease will help assess the effect of treatments, such as gene therapy, by comparing the treated to the untreated patients.”
Once restricted to adults and involving only one eye, gene therapy trials have expanded to include children and involve both eyes.
The research will take time, though. Researchers must find a virus capable of carrying different genes and of different sizes. “Delivering gene therapy to the eye is technically challenging but perfectly doable with current surgical techniques,” notes Dr. Traboulsi.
The long-term effectiveness of gene therapy and the need for retreatment are also being examined.
The safety of delivering gene therapy to the eye is also a concern. “It is critical to avoid spreading the virus to the central nervous system or triggering an immune response that leads to eye inflammation and further impacts vision,” he says. “Such issues are major considerations in current treatment trials.”