A simple gene therapy injection could cure colour blindness, a condition that affects one in 12 men and one in 230 women, often preventing them from taking on careers as pilots, police and electricians, as well as limiting their night vision, and putting themselves and others at risk.
The work is a culmination of more than eight years by researchers at the Eye Institute of the University of Washington in collaboration with laboratories at the University of Florida and the Medical College of Wisconsin.
The researchers have successfully used gene therapy to cure colour blindness in adult monkeys. Prior to treatment, the monkeys were trained to touch the location of a coloured patch hidden among grey dots similar to the well-known testing books in which coloured numbers or symbols are concealed in a pattern of dots. Similar to colour-blind humans, the monkeys could not distinguish red or green, but following treatment that added the missing visual pigment gene, they passed the test easily for all colours.
A popular belief has been that ‘critical periods’ for the development of many capacities end prior to adolescence, implying that treatments involving the adult visual system would be impossible. To the contrary, the results of Mancuso and colleagues reported in Nature indicate that in the case of colour vision, the nervous system is capable of responding to newly-added sensory input, allowing adult monkeys to respond to colours that they could not see previously.
“the encouraging results of both studies open the way to treatments for a broad range of
eye diseases…
According to the researchers, this success in treating colour blindness complements ongoing gene therapy trials for the blinding disorder, Leber’s congenital amaurosis (LCA), a progressive disease that causes cell death and retinal degeneration. The initial phases of the LCA trials are safety studies in which a therapeutic gene was administered to patients with advanced disease. Early results indicate that the treatment is safe; however, the effectiveness of the therapy for LCA will not be known until younger patients with healthier retinas are treated. In contrast to LCA, retinal degeneration is not associated with colour blindness and its successful treatment demonstrates the full potential of gene therapy to restore a visual capacity.
As most vision disorders have a genetic component involving the retina, the encouraging results of both studies open the way to treatments for a broad range of eye diseases.
The prospect of ameliorating the problems caused by colour blindness makes it an attractive future target for human gene therapy. Because the monkey visual system is similar to that of humans, and a human gene was used to replace the missing visual pigment of the monkeys, the scientists are optimistic about the possibility of gene therapy to cure colourblindness in humans. While no adverse side-effects were observed in the monkeys, the most important barrier in moving the treatment forward will be ensuring its safety for use in humans.
