Gene therapy cures colour blindness

Researchers in the United States have used gene therapy to allow colour blind monkeys to see in full trichromatic glory. It it hoped that similar techniques could be used to cure a spectrum of adult vision disorders.

The researchers focused on squirrel monkeys that were missing the L-opsin gene, which is involved with visual sensitivity to longer wavelengths of light. Some female squirrel monkeys have trichromatic colour vision whereas males lack the gene and are red-green colour blind.

They then introduced a human version of the L-opsin gene in to the male monkeys via a serotype 2/5 recombinant adeno-associated virus (rAAV) delivered by subretinal injections. The gene was regulated to preferentially express in medium wavelength M cones rather than short wavelength S cones, converting some of the M cones into effective L cones.

The monkeys were then tested on a Cambridge Colour Test adapted for animals and the treated monkeys were found to be able to distinguish colours that were not perceived by the dichromatic monkeys.

One surprising result was that adult monkeys who had developed dichromatically could still be treated and respond to the trichromatic tests. It was believed that trichromatic vision would have to be in place at a very early age in order for the brain to respond to it correctly. However, these monkeys were able to 're-wire' their brains even in adulthood.

It's possible that similar treatments might one day allow colour blind humans to be able to develop trichromatic vision.

The research was published in Nature and was led by Katherine Mancuso and colleagues at the Department for Ophthalmology at the University of Washington in Seattle, University of Florida and Medical College of Wisconsin.