Cutting Edge Gene Therapy Provides Hope for Patients with Inherited Eye Conditions

April 25, 2017

Imagine stepping out into a bright South Florida morning — and literally being so sensitive to light that it causes painful blindness. Imagine, too, being unable to discriminate between colors and slowly (and reluctantly) adapting to losing your sight.

For those suffering from achromatopsia (ACHM), a rare inherited condition with no cure, these situations are a reality. But now a clinical trial at four different U.S. sites, including University of Miami’s Bascom Palmer Eye Institute, is providing, quite literally, a ray of hope for those who suffer from this gene mutation.

The trial will evaluate a cutting-edge concept: gene therapy. While there are no gene therapy products currently approved for use in the U.S., researchers are experimenting to see if they can provide a solution to alleviate hereditary diseases. Gene therapy has become one of the more exciting areas of biotechnology.

“For years, patients who had hereditary retinal diseases didn’t really have much hope,” said Dr. Byron Lam, a neuro-opthalmologist who specializes in hereditary retinal degenerations at UM’s Miller School of Medicine. “They were diagnosed, but there wasn’t anything anyone could do about it. Now there is hope. It’s the first time we can say, ‘We might be able to do something about this.’”

Lam, who is also a professor of ophthalmology, and his colleagues are recruiting volunteers for a study that evaluates a gene therapy product, AGTC 402, developed by Applied Genetic Tecnnologies Corp. in the treatment of ACHM. The clinical trial is in its early stages, so it will look at the safety and efficacy of the therapy for about two to three years. 


Those who inherit ACHM suffer from decreased vision, light sensitivity and the absence of color vision. In the U.S., the condition affects about 1 in every 33,000 people, and it is typically diagnosed by the time children are 2. Some patients have no family history of the condition, Lam said. Currently, ACHM patients are treated with prescription eyeglasses or contacts to improve vision and red-colored lenses to reduce sensitivity to light.

Achromatopsia is caused by mutations in any of several genes that result in a retinal abnormality. “Before the discovery of these genes [in the late 1990s],” Lam said, “the condition had been recognized for decades, but we knew little about addressing it. There was no gene technology.”

Two of the genes that cause ACHM — CNGB3 and CNGA3 — account for at least 75 percent of ACHM cases. The Bascom Palmer trial will evaluate CNGB3 by using a novel therapy to treat the mutated gene.

Typically, a mutated gene provides incorrect information to a cell, which, in turn, produces an abnormal protein. The idea of gene therapy is to deliver a correct, or functional, copy of the gene into a patient’s cell and have the normal protein produced by the functional gene correct the causes of the disease. The therapy uses engineered viruses to deliver these functional genes. In the case of the ACHM trial, the functional genes will be injected under the retina.

Gene therapy for AGTC has already been tried in dogs and sheep with the condition, Lam said. In those cases, the normal copy of the defective gene restored enough vision for the animals to navigate a maze.

The upcoming multi-site clinical trial is good news not just for those with ACHM but for all who have hereditary retinal conditions. Success with one could lead to breakthroughs in others.

Delray Beach mother Suzi Ford is South Florida director for MOMS for Sight, a nonprofit that raises money for sight-saving research. One of her two sons has choroideremia, a progressive inherited condition that leads to vision loss and ultimately to complete blindness. Choroideremia has affected four generations of Ford’s family and now her 26-year-old son is going blind. She believes gene therapy is the closest medical research has come to a cure.

“If it works, it can have a domino effect,” she said. “What they discover [for ACHM] can be modified and then applied to other retinal degenerative diseases — or any disease caused by a gene mutation. It can really open the world for people. It’s hard to describe how huge this can be.”

Lam, however, has a word of caution. Even if this initial clinical trial on humans is successful, the road to market is still a long one.

“Nobody really knows how long [before the therapy is on the market],” he said. “It could be eight, nine, 10 years from now, if everything goes superbly.”

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