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K. Mancuso, M. Neitz, W. W. Hauswirth, Q. Li, T. B. Connor, J. A. Kuchenbecker, M. C. Mauck, J. Neitz; Long-Term Results of Gene Therapy for Red-Green Color Blindness in Monkeys. Invest. Ophthalmol. Vis. Sci. 2010;51(13):6292.
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Red-green color blindness, which results from the absence of either the long- or the middle-wavelength-sensitive visual photopigments, is the most common single locus genetic disorder. We reported previously that adding a third photopigment to the retinas of adult dichromatic squirrel monkeys (Saimiri sciureus)via gene therapy was sufficient to confer trichromatic color vision (Nature, 2009; 461: 784-7). The goal of the present study was to monitor long-term effects of the treatment.
Two male dichromatic squirrel monkeys, born with only short- and middle-wavelength-sensitive cones, received subretinal injections of a recombinant adeno-associated virus vector containing a human long-wavelength sensitive opsin gene. Their color vision capacities were assessed using a computerized color vision test, the Cambridge Colour Test, which was adapted for use with the monkeys. Effects of the treatment have been monitored over the 3.5 years since they were treated.
No negative side-effects from the treatment have been observed. While normal trichromats have four main hue percepts - red, green, blue, and yellow, - dichromats can discriminate blues and yellows from gray, but lack percepts of red and green. The treated dichromatic squirrel monkeys have continued to make color discriminations that are impossible for their untreated dichromatic counterparts. The dramatic gains in color vision remained stable 3.5 years after treatment.
The long-term success of treatment for red-green color blindness in adult primates is encouraging for the possibility of using gene therapy to treat a variety of cone photoreceptor-based vision disorders in humans. Treated monkeys will continue to be monitored with regular fundus exams, the wide-field color multifocal electroretinogram, and behavioral color vision testing.
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