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IN A dramatic demonstration of the power of gene therapy, dogs with a rare
inherited form of blindness have had their sight restored. The work could be an
important step towards the treatment of eye diseases in humans.

鈥淚t is the sort of result, that if you are lucky, you see once in your
career,鈥� says Jean Bennett of the University of Pennsylvania in Philadelphia.
鈥淲e are really excited.鈥�

The dogs in the study had a naturally occurring eye disease called Leber
congenital amaurosis (LCA), which causes the light-sensing tissue of the retina
to malfunction and degrade. LCA also occurs in people. Sufferers usually lose
their vision in infancy.

The condition can be caused by a mutation in one of three known genes.
Defects in other, as yet unknown, genes may also cause the condition. The dogs
in the study had a defect in the gene for a protein called RPE65, which helps
create a pigment necessary for normal vision.

So Bennett and her colleagues engineered a good copy of the gene into an
adeno-associated virus and injected it directly into the retina of the right
eye of three dogs. The result was an enormous boost in electrical activity and
pupil function in the right eyes.

As controls, the virus was injected only into the eyeball fluid of the left
eye of two of the dogs, while the left eye of the third dog was not given any
injections. These eyes showed no signs of improvements.

But the moment of truth came when the dogs had to navigate a poorly lit
obstacle course of tables and chairs. The animals were able to deftly steer
around objects in front of them and to their right. 鈥淲ithout the treatment, they
bumped into things like a pinball in a machine,鈥� says Bennett.

So far, there don鈥檛 appear to be any side effects or strong immune responses
to the treatment. 鈥淚t鈥檚 a really excellent paper, a large contribution to the
field,鈥� says John Flannery, who works on eye gene therapy at the University of
California, Berkeley.

The work could lead to a treatment for LCA in people. However, it鈥檚 not yet
clear whether such treatments would work for older people whose retinal
structures may have degenerated beyond repair.

The lessons learned about virus delivery and gene activation should also help
researchers develop treatments for more common diseases such as age-related
macular degeneration, which is responsible for half of all blindness in people
over 50. Bennett and her colleagues are following the dogs to see if any
problems develop and how long the treatment will last.