Researchers used gene therapy to cure two squirrel monkeys of colour blindness - the most common genetic disorder in people. The work, in this week's Nature, demonstrates the potential for gene therapy to cure adult vision disorders involving cone cells - the most important cells for vision in people.
Adding new sensory information, such as visual receptors sensitive to different wavelengths of light, to the brain would only be possible in the early years of life, when the brain is at its most plastic. The scientists now show that, in the case of distinguishing colours, this may not be true.
The team tested male squirrel monkeys that are known to be red-green colour blind. Using a variety of biophysical and behavioural tests they showed that by introducing genes for photopigments present in some female monkeys, although never in males, into photoreceptor cells in their retina, male monkeys can be given the ability to distinguish between red and green colours, which they previously could not.
By showing that it is possible to add sensory abilities to primates, the finding indicates that the brain may be able to re-wire itself with completely new information, even when the assumed critical period for brain plasticity and development is over. Although it may be some distance off, this could lead to opportunities for adding or restoring functions to the eye.
The finding is likely to intrigue millions of people around the world who are colour blind, including about 3.5 million people in the United States, more than 13 million in India and more than 16 million in China. The problem mostly affects men.