Gene Therapy Cures Color Blindness in Monkeys

Thanks to gene therapy, this monkey can distinguish shades of red and green.
Thanks to gene therapy, this monkey can distinguish shades of red and green.

If nature gave you some bum genes, you’ve got a chance of fixing them. Genetic treatments have allowed researchers to cure color blindness in two squirrel monkeys. As published this month in Nature, gene therapy allowed two males to begin producing the L-opsin protein that allowed them to finally see reds and greens. Besides viewing the world in color, what’s the benefit of genetic treatments? Endless supplies of grape juice. Check out the short video below of one of the monkeys getting a reward for identifying red spots during a test.

When any form of blindness has a genetic cause, the promise of restored sight through genetic treatment lingers. We saw the first such case of gene therapy restoring sight when it was used to cure Leber’s congenital amaurosis (LCA) in human children. Those tests were revolutionary, but monkey technicolor vision is remarkable as well. Most scientists believed that adult brains do not have the same rewiring capabilities and plasticity as young brains. Yet the two adult monkeys, Sam and Dalton, started receiving and comprehending new signals once the L-opsin gene was introduced into their retinas.

All male squirrel monkeys are color blind, making them ideal for the test. Furthermore, the mechanism for their color blindness (the lack of L-opsin protein) is similar to many cases of human color blindness. The same method of gene therapy that was used in the LCA tests, was adapted to help monkeys produce opsin. First, scientists knew which gene codes for L-opsin production. A virus was created to carry that gene. The virus was then injected into the monkey’s retina. Like any self-respecting virus, it infected cells and in the process passed on the new gene. These upgraded cells in the retina now had the gene to produce L-opsin and boom…monkeys see in full color.

While the research was only recently published, it took place over several years. After gene therapy, it took five months of rewards-based testing (like that in the video) to discover that the squirrel monkeys could detect shades of red. It is unclear if that time was due to the slow development or adaptation of neural pathways, or the cognitive progression of the monkeys. In fact, the mechanism for how the monkeys’ brains were changed to receive the new input is not well understood at all. The change is likely very stable – the monkeys have retained their new color perception for the more than two years that have passed since testing began.

The fact remains that we are years from seeing color blind gene therapy being offered to humans. It is obviously still in the animal testing phase. The LCA treatment was for safety testing, not efficacy testing, so there are years of study ahead in that field as well. Still, genetic treatments are advancing and could one day be used to cure advanced macular degeneration (AMD), and other common forms of blindness.

And gene therapy isn’t just limited to the eye. Cures for almost any genetic condition could be done in a similar manner to the blindness treatments. In theory, all it takes to fix an illness is finding the responsible gene and replacing it. We could see these treatments rise in availability in the next ten to twenty years.

Gene therapy could also allow us to update our genes so that we could view colors outside our natural range, or develop low-light vision as good as other animals. Enhancements for oxygen absorption could make super athletes out of everyone.  Such possibilities are likely decades away, but they’re not out of the question.