Gene Therapy Cures Color Blindness in Monkeys

By Eliza Strickland | September 16, 2009 7:25 pm

color-blind-monkeyFor two squirrel monkeys nicknamed Dalton and Sam, life has gotten a lot more colorful. Researchers used gene therapy to correct the color blindness of the two adult monkeys, giving them the ability to distinguish between red and green for the first time. The fascinating accomplishment suggests that scientists may someday be able to cure other kinds of blindness in humans. And because the treated monkeys were “middle aged”, it challenges the assumption that gene therapies cannot work in adults because their brain connections are too set in their ways to change beneficially [New Scientist].

The field of gene therapy, in which a malfunctioning gene in a patient’s body is replaced with a functional one, fell into disarray one decade ago following the death of an 18-year-old in a clinical trial. But since then scientists have regrouped, using animal studies to probe the technique’s safety. Last year, researchers progressed to the point of safety trials in humans for the treatment of one rare eye condition called Leber congenital amaurosis, and were able to dramatically improve the patients’ sight. Those results were stunning, but they were also achieved in children, whose still-growing brains can rewire themselves on the fly in response to new sources of visual stimuli [].

In the new study, published in Nature, the researchers used a type of squirrel monkey in which the males lack a visual pigment called L-opsin. Its absence renders the monkeys color-blind, unable to distinguish reds and green. Most of the females, on the other hand, see in full color. So the scientists got to wondering: what would happen if they gave a boy squirrel monkey the same opsin that girls have [Scientific American]. They used a harmless virus to ferry in the gene that makes opsin, injecting the virus behind the monkeys’ retinas.

color-blind-monkey-3The results were dramatic. The monkeys had already been trained to recognize patterns of blue and yellow dots against a gray screen in order to get a grape juice reward. About 20 weeks after the procedure, they began to also recognize the patterns of green and red dots that they had previously ignored. Two years on, the monkeys can still see the colors and have experienced no obvious side effects.

The researchers say that the work’s most interesting aspect is that the monkeys gained full-color vision even though their adult brains couldn’t grow new neural circuits. Instead the existing neural circuitry and visual pathways apparently adapted to make use of the new opsin pigment that was suddenly produced in the eye. This realization will open the way for new research on treating a wide range of eye disorders in adults.

Study coauthor Jay Neitz says the findings could, theoretically, lead to work that goes beyond curing eye diseases, and forges ahead into eye enhancements. One very speculative and futuristic possibility is that of using gene therapy to equip humans to see ranges of light invisible to them at present, such as ultraviolet or infrared light. Some birds and reptiles can sense UV light, for example, and some fish can sense wavelengths approaching those in the infrared. “I wouldn’t rule it out completely, but it’s very futuristic,” says Neitz [New Scientist].

But enough of the medical implications of the research. Here’s a pressing question: What must it have been like for the monkeys to suddenly see the world in full color? While we can’t get an answer from Dalton and Sam, Neitz is willing to speculate. “You go out and look at a rainbow, or the fall leaves, or sunset over the ocean, and it’s not something where you just say, ‘I can see colors.’ It has a deep effect on us,” he said. “These emotions are something we inherited from our evolutionary past. I think monkeys have that, too. I think these animals must have the real experience of, “Oh! Wow!” []

Related Content:
80beats: Gene Therapy Restores Sight to the Blind
DISCOVER: The Second Coming of Gene Therapy

Image: Neitz Laboratory

CATEGORIZED UNDER: Feature, Health & Medicine
  • nick

    “One very speculative and futuristic possibility is that of using gene therapy to equip humans to see ranges of light invisible to them at present, such as ultraviolet or infrared light. Some birds and reptiles can sense UV light, for example, and some fish can sense wavelengths approaching those in the infrared.”

    Put me down on the waiting list.

  • Christina Viering

    Fascinating study!

  • Andrew

    forget ultraviolet or infrared. i just want my color vision!

  • jesseca

    it’s exciting yes, but then you think about how many monkeys had to die for this study and it makes you wonder.

  • Hyldren Shelton

    I have Chordoma tumors in lower spine why can’t they do gene therapy on me? Look up on the internet for
    Thank you, if you can get back to me real soon…

  • Hyldren

    Because of risks of rampant immune response in non-eye gene therapy..Good luck…

  • Claire Warton

    To genetic scientists, I have a question. Is anyone willing to try Mimiviruses skills to create , with the use of stem cells, T-cell repellant Myelin? New undamaged/undamageable neuronal pathways for humans? New pathways have been achieved for mice and dogs, but not for humans. Would Pigs be the next mammal to try, since their heart valves are used in Human Cardiac Surgery with success? How far up the train of Species would one need to go before feeling it safe to try on Humans?

    I am living with the effects of Multiple Sclerosis, this my 28th year, at age 50. Perhaps people who have signed up as organ donors when they die could also have the option of artificial life sustenance. At that stage, if cause of coma or near death is a brain injury, when there is every sign that the brain is no longer viable, new neuronal pathways could be introduced. I do ask very sincerely as I know this would advance medicine for all sorts of Neurological damage. Perhaps Christopher Reeves did not have to die if scientists had been given more support to pursue new neuronal pathways. I do not know how the eyes can be selected for treatment as an isolated organ. Do the neurons diversify on their on to areas of malfunction or damage?

    I wish to create a Corporation to fund Neuroscience research in this area. This is impossible if their is no scientist globally who would like to take on the work. Much is being done in the way of stem cells to create new organs, but nothing to counteract vulnerable Myelin. Please contact me at You may also contact my husband Peter at Thank you. We look forward to your reply.

  • Chuck

    DARPA should probably fund studies on visual spectrum enhancement in squirrel monkeys (none need die; the monkey’s behavior tells all). I’d start with IR and then go for UV. The next step is human trials. As an artist, I volunteer so that I may convey the results visually; as a scientist, I volunteer for the sake of exploration; as an engineer, I volunteer for the sake of progress. I’ll offer my left eye only, with my right eye as a control. As for curing disease, let’s start with this project as a basis for further exlorations in enhanciing or repairing the human nervous system, starting with the retina.

  • Joel

    @jesseca If it wasn’t for numerous research on different animals everyone would have polio right now, please take the time to quit embracing your trees and broaden your knowledge on both sides of the table.

  • John Lerch

    I’ve been complaining about Discover’s reporting, so I need to send kudos too. The information that the monkeys somehow saw color without creating new neural pathways was right on.
    And relative to the silly comment that monkeys had to die for this experiment,–there certainly isn’t any evidence that any monkey died. And MORE IMPORTANTLY as the researcher commented if the same experiment were successfully done to a human, he’d be saying Oh WOW! I.E. instead of harming the monkeys they enhanced their quality of living.


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