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Using a virus to deliver new genes to vision cells unable to produce a protein necessary for sight, researchers turned on the dogs' ability to produce the protein, giving them back their ability to see.
Within the next six months US researchers will embark upon the first trial of gene therapy to treat genetic blindness in humans, Professor John Flannery, from the University of California, Berkeley, said at a recent lecture in Cape Town.
Watch the dogs in this video
Here's the proof. Watch this video of two dogs, one untreated and still blind, while the second dog can see after gene therapy. In order to view the video, you need to download Quicktime. Then click here to watch a video of the dogs. Be patient, the download may take a few minutes, but the wait is worth your while. Note how the black dog (still blind) struggles at the beginning of the video to find his way. He is unsure, and bumps into all obstacles to his left and right. The white dog (treated in his right eye), does not bump into any obstacles to his right, but only on his left (blind) side. We bring you this video, thanks to Dr Jean Bennett, associate professor of ophthalmology at the University of Pennsylvania in Philadelphia, USA and the woman behind the research. Send the video to a friend.
The specific condition is called Leber's congenital amourosis (LCA), and is similar to the condition that was successfully treated in dogs.
LCA is a rare genetically inherited condition that leads to dysfunction of the retina. It usually causes severe visual impairment, often from birth.
Damage to the film
The retina can be thought of as the film in your eye. Thus, if the retina is damaged, no adaptation with glasses or lenses can fix the problem – the retina itself needs to be treated.
The process by which visual information is transferred from the front of the eye, the cones and rods, through the eye, and to the brain is an extremely complex one. Gene defects can cause problems anywhere along the line, and figuring out which genes cause which problems is keeping researchers very busy at present.
In the specific form of LCA that is to be treated in the coming trial, there is a defect in the gene that tells the eye to reshape vitamin A molecules at a particular point during its journey in the eye. As a result, the vitamin A molecules cannot do their work, and the functioning of the retina is impaired.
LCA causes a variety of other eye-related abnormalities, including roving eye movements, deep-set eyes and sensitivity to bright light. Some patients with LCA also experience central nervous system abnormalities.
It is estimated that about 2000 South Africans may suffer from the disease, from extrapolated figures.
Restoring normal vision
The aim of the gene therapy would be to introduce the correct gene into the eye. This will, one hopes, instruct the eye to reshape the vitamin A molecules in the correct way, and the normal process of vision would hopefully be restored.
Bennett and her team tested the gene therapy on three dogs with a genetic disease that mimics Leber congenital amaurosis (LCA).
Using a virus
Bennett and her colleagues used a virus to deliver new genes to the dogs' rod and cone cells by loading
up a recombinant virus with the gene. (Rod and cone cells are at the back of the eye. They sense light, color, and shape and send messages to the brain.) The gene then enters the nucleus of the target cells, which then begin to process the appropriate protein, Health Day News reported.
- "We placed a contact lens on the dog's eye, and then flashed light at the eye and measured electrical response. That's a test that's routinely given to humans. The test showed electrical signals where they didn't exist before.”
- The second test demonstrated that vision was actually processed by the brain. Prior to gene therapy the pupil did not grow smaller when light was shone into the dogs’ eyes , but after the therapy, it did.
- Finally, the dogs were able to walk around without bumping into things. The dogs were at first mystified. But after a while they became very happy and began wagging their tails, according to Bennett.
"This borders on the miraculous," says Tom Hoglund, communications director for the American Foundation for Fighting Blindness, according to Health Day News.
– (Marcus Low, Health24)
Read more:
Eye Centre
To wish upon a Stargardt miracle
September 2006
Useful resources:
South African Optometric Association
Tel: 011 805 4517
South African National Council for the Blind
Tel: 012 452 3811
Retina South Africa
Tel: 011 622 4904
