Gene Therapy Cures Color-Blind Monkeys

After receiving injections of genes that produce color-detecting proteins, two color-blind monkeys have seen red and green for the first time.

Except in its extreme forms, color blindness isn’t a debilitating condition, but it’s a convenient stand-in for other types of blindness that might be treated with gene therapy. The monkey success raises the possibility of reversing those diseases, in a manner that most scientists considered impossible.

The team injected their monkeys’ eyes with viruses carrying a gene that makes L-opsin, one of three proteins released when color-detecting cone cells are hit by different wavelengths of light. Male squirrel monkeys naturally lack the L-opsin gene; like people who share their condition, they’re unable to distinguish between red and green.

At first, the two monkeys behaved no differently than before. Though quick to earn a grape juice reward by picking out blue and yellow dots from a background of gray dots on a computer screen, they banged the screen randomly when presented with green or red dots.

But after five months, something clicked. The monkeys picked out red and green, again and again. At the biological level, scientists can’t say precisely what happened — the monkeys, named Sam and Dalton, are alive and healthy, their brains unscanned and undissected — but their actions left no doubt.

Read more about the implications of the findings here.