Scientists Cure Color Blindness in Monkeys

(Ivanhoe Newswire) -- Researchers from the University of Washington and the University of Florida have used gene therapy to cure two monkeys of color blindness.

Scientists cast a rosy light on the potential for gene therapy to treat adult vision disorders involving cone cells, which are the most important cells for human vision. "We've added red sensitivity to cone cells in animals that are born with a condition that is exactly like human color blindness," William W. Hauswirth, Ph.D., a professor of ophthalmic molecular genetics at the University of Florida College of Medicine was quoted as saying. "Although color blindness is only moderately life-altering, we've shown we can cure a cone disease in a primate, and that it can be done very safely. That's extremely encouraging for the development of therapies for human cone diseases that really are blinding."

Color blindness affects about 3.5 million people in the U.S., more than 13 million in India and more than 16 million in China. The problem is more prevalent in men, leaving about 8 percent of Caucasian men in the U.S. incapable of identifying red and green hues -- important for routine activities like getting dressed and recognizing traffic lights.

"People who are colorblind feel that they are missing out," Jay Neitz, Ph.D., a professor of ophthalmology at the University of Washington, was quoted as saying. "If we could find a way to do this with complete safety in human eyes, as we did with monkeys, I think there would be a lot of people who would want it. Beyond that, we hope this technology will be useful in correcting lots of different vision disorders."

The discovery comes about 10 years after Neitz and his wife Maureen Neitz, Ph.D., a professor of ophthalmology at the University of Washington and senior author of the study, began training two squirrel monkeys named Dalton and Sam. In addition to teaching the animals, the Neitz research group worked with the makers of a standard vision-testing technique called the Cambridge Color Test to perfect a way the monkeys could "tell" them which colors they were seeing.

The tests are similar to ones given to school children, in which students are asked to identify a specific pattern of colored dots among a field of dots that vary in size, color and intensity. The researchers devised a computer touch screen the monkeys could use to trace the color patterns. When the animals chose correctly, they received a reward of grape juice.

Meanwhile, Hauswirth and colleagues at the University of Florida were developing a gene-transfer technique that uses a harmless adeno-associated virus to deliver corrective genes. The researchers sought to produce in the retinas of the monkeys a substance called long-wavelength opsin, a colorless protein that works in the retina to make pigments that are sensitive to red and green.

"We used human DNAs, so we won't have to switch to human genes as we move toward clinical treatments," said Hauswirth. About five weeks after the treatment ended, the monkeys began to acquire color vision.
 
"Nothing happened for the first 20 weeks," Neitz said. "But we knew right away when it began to work. It was if they woke up and saw these new colors. The treated animals unquestionably responded to colors that had been invisible to them."

"We've had Dalton and Sam for 10 years. They are like our children," Neitz said. "This species are friendly, docile monkeys that we just love. We think it is useful to continue to follow them — it's been two years now that they've been seeing in color, and continuing to check their vision and allowing them to play with the computer is part of their enrichment."

With the discovery, the researchers are the first to address a vision disorder in primates in which all photoreceptors are intact and healthy, providing a hint of gene therapy's full potential to restore vision.
Even in common types of blindness, such as age-related macular degeneration and diabetic retinopathy, vision could potentially be rescued by targeting cone cells, said Neitz.

"The major thrust of the study is you can ameliorate if not cure color blindness with gene therapy," Gerald H. Jacobs, Ph.D., a research professor of psychology at the University of California, Santa Barbara, who was not involved in the research, was quoted as saying. "This is also another example of how utterly plastic the visual system is to change. The nervous system can extract information from alterations to photopigments and make use of it almost instantaneously."

SOURCE: Nature, September 16, 2009