So far, only in monkeys

Sep 17, 2009 05:30 GMT  ·  By

Experts at the University of Washington in Seattle have recently announced the first successful treatment of color blindness using gene therapy, in squirrel monkeys. The method has been applied on animals that were born with the condition, not that developed it over the course of their lifetimes. The new research brings forth new hope of finding a cure for the condition, which adversely affects the quality of life of many people suffering from it as well, Nature News reports.

“This is a truly amazing study. If we can target gene expression specifically to cones [in humans] then this has a tremendous implication,” University of Pennsylvania in Philadelphia veterinary ophthalmologist and vision researcher Andras Komaromy says. He has not been directly involved in the new study. Details of the amazing feat are published in the latest issue of the renowned scientific journal Nature. The paper shows how these experiments could be used on other visual impairments as well.

Saimiri sciureus, the squirrel monkey, is the perfect animal model for color blindness. In order for humans or monkeys to see green and red, they have to have two versions of a gene known as opsin. One of these versions codes the green photoreceptors on the retina, while the other codes the red ones. Because male S. sciureus monkeys have only one X chromosome, they see the world in just two tones. Females, on the other hand, carry two X chromosomes, and are therefore able to see both colors. “Here is an animal that is a perfect model for the human condition,” UWS team member Jay Neitz shares.

In their experiments, the scientists used the human form of the red-detecting opsin, and attached it to a viral agent, which they then injected behind the retina of the animals (one named Dalton, and the other Sam). Afterwards, the monkeys were made to identify patches of color on a screen, and were trained to touch it whenever they saw specific colors. After about 20 weeks, the experts report, both Dalton and Sam experienced a massive improvement in color-detection skills, and no negative side-effects could be traced back to the gene therapy more than two years after it was applied.

“It doesn't seem like new neural connections have to be formed. You can add an additional cone opsin pigment and the neural circuitry and visual pathways can deal with it,” Komaromy adds. “There is this plasticity still in the brain and it is possible to treat cone defects with gene therapy,” University College London molecular biologist and vision researcher Alexander Smith, who has not been directly involved in the research, concludes.