GMA: Gene Therapy Helps Blind Dogs See

Scientists have injected new genes into the eyes of blind dogs and gave them sight for the first time. Now they are hoping the same technology can be used to bring vision to children who have been blind since birth.

A team of scientists led by University of Pennsylvania researchers produced sight in three puppies that were genetically blind from birth. It is the first time that congenital blindness has been reversed in an animal larger than a mouse. The researchers replaced a mutant gene that caused blindness with a gene that they had created in a lab.

Within a few weeks after the injection, the dogs could see enough to follow human movement and to negotiate a path around furniture.

"We didn't expect a result this spectacular," said Dr. Jean Bennett of the Scheie Eye Institute on today's Good Morning America.

"We were really very, very excited when we first got a glimmer that we had actually restored vision to these dogs which had been previously blind."

Could Help Blind Children

The findings have implications for the nearly 10,000 people with a genetic disease called Leber congenital amaurosis (LCA), the same disease that caused the blindness in the dogs. It could also help hundreds of thousands of others with similar forms of blindness.

Over time, the retina deteriorates and becomes dysfunctional in people with this disorder, so scientists say children would be the most likely beneficiaries of the gene therapy. Children with LCA are destined to a life of blindness: they will use guide dogs and read and write in Braille.

There is a lot to be done first before researchers can advance to human trials, said Dr. Gregory Acland, a research veterinarian at Cornell University. Acland says he expects it will take about four years to get to that point.

Researchers have to look at a variety of factors. Human vision is different from dog vision because there is a different sense of acuity. Researchers would also have to determine the dose, and the frequency of the treatments for humans.

Also, gene therapy has a 10-year history of raising false hopes, and the field has been under critical scrutiny since the November 1999 death of a teenager in a gene therapy experiment.

As a result, scientists would want to make sure that the therapeutic effect is long term without complications or side effects.

Next Step: Catching a Frisbee?

In the study, the gene was injected under the retina in one eye of each of the three Briard dogs, Acland said. The dogs are blind because of a genetic mutation acquired over the course of long-term breeding by humans.

It took a month or so for the gene to start working in the retina. Then, the scientists tested the functioning level using a technique known as elecro retinography, which measures the electrical activity in the retina.

In normal circumstances, with this condition, you would expect only very tiny responses, but after just eight weeks the first dog showed retinal activity was 35 to 40 percent of normal, a dramatic result, Acland said. Researchers only treated one eye because if something went wrong, it would only happen in one eye, he said.

In researchers' video of one of the dogs, it is obvious that he follows movement, and the dog's caretakers also noticed that the dog was watching them with his right eye, said Bennett. They hope one day he'll be able to catch a Frisbee.

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