January 16, 2014
New Gene Therapy For Blindness Shows Promise
Brett Smith for redOrbit.com - Your Universe Online
A newly developed genetic therapy for treating a type of inherited blindness called choroideremia is showing some promise and allowing patients to see incrementally more than they had before the treatment, according to a new report in The Lancet.
Six patients in the study had one eye treated with the gene therapy in operations at the Oxford Eye Hospital in the United Kingdom. After six months, the treated eye showed improved vision in dim light compared to the untreated eye, and two of the six patients could successfully read more lines on an eye chart than before the treatment.
“My left eye, which had always been the weaker one, was that which was treated as part of this trial,” said Jonathan Wyatt, the first patient to be treated. “Now when I watch a football match on the TV, if I look at the screen with my left eye alone, it is as if someone has switched on the floodlights. The green of the pitch is brighter, and the numbers on the shirts are much clearer.”
Caused by defects in the CHM gene on the X chromosome, Choroideremia affects approximately 1 in 50,000 people, almost all males. The first symptoms of the condition typically crop up in boys during the later stages of childhood. The incurable disease gradually advances until vision is completely gone. Without a protein coded by the CHM gene, pigment cells in the retina of the eye gradually stop functioning and then die off. As the condition advances, the retina slowly shrinks in size from cell loss, eliminating vision.
The new therapy utilizes a specially engineered virus to deposit a properly functioning CHM gene into the retina. Once the gene is delivered into the retina, it begins to produce protein and prevent cell die off.
“If we were able to treat people early, get them in their teens or late childhood, we'd be getting the virus in before their vision is lost," said study author Robert MacLaren of the Nuffield Laboratory of Ophthalmology at the University of Oxford. “If the treatment works, we would be able to prevent them from going blind.”
“'It is still too early to know if the gene therapy treatment will last indefinitely, but we can say that the vision improvements have been maintained for as long as we have been following up the patients, which is two years in one case,” he added.
McLaren added that the new treatment has potential for treating other retina conditions such as age-related macular degeneration, “because it has for the first time shown that gene therapy can be applied safely before the onset of vision loss.”
After the promising results were seen in the first six patients, three more patients were administered a higher dose of the gene therapy. Wayne Thompson, 43, was treated in April as part of the follow-up trial.
"One night in the summer, my wife called me outside as it was a particularly starry evening. As I looked up, I was amazed that I was able to see a few stars. I hadn’t seen stars for a long, long time,” he said. “For a long time I lived with the certainty of losing vision. Now I have uncertainty of whether the trial will work, but it is worth the risk.”