Penn researchers report gain in using gene therapy to battle blindness

Four years ago, teams of researchers at the University of Pennsylvania and elsewhere made headlines by restoring some sight to blind people, though it was a form of blindness few had heard of.

Now some of the same researchers are making progress with a far more common kind of blindness, retinitis pigmentosa, which strikes many thousands.

This week, the scientists reported success in treating four dogs with forms of the disease. And they are optimistic that their findings will, like the earlier study, translate to humans.

As before, the new effort involved injecting healthy genes into the retina to compensate for mutated, malfunctioning genes. Known as gene therapy, this concept is fairly young but is starting to show promise with a few diseases, including a type of hemophilia.

In the dogs, the gene injections stopped the eye disease in its tracks - preventing the onset of severe symptoms and, to some extent, reversing early signs of damage, the scientists reported in Proceedings of the National Academy of Sciences.

The research was led by Gustavo D. Aguirre and William A. Beltran of Penn's School of Veterinary Medicine, along with ophthalmologists Artur V. Cideciyan and Samuel G. Jacobson of Penn's Perelman School of Medicine. Scientists at the University of Florida created the "vector" - a modified virus - that was used to deliver the corrective genes to the dogs' eyes.

While it isn't the first time researchers have used gene therapy to treat blindness, the latest effort is significant in that it tackled a disease that afflicts two kinds of cells - rods and cones, said a scientist in the same field who was not involved with the work.

"This is a big advance," said John G. Flannery, a professor of neurobiology at the University of California, Berkeley.

It's unclear just how many people have the kind of blindness that was treated in the dogs, but the number is apparently in the many thousands.

The animals were born with mutations in a gene called RPGR, which is a rare occurrence in dogs but relatively common in people. Such mutations account for most human forms of a kind of retinitis pigmentosa known as "X-linked" - meaning that the defective gene is located on the X chromosome.

X-linked retinitis pigmentosa is one of the most common kinds of retinitis pigmentosa, which has been estimated to affect tens of thousands of people in the United States, though Penn's Jacobson said a reliable total was not available.