Jordan Garboski
jeg2005@wildcats.unh.edu

Abstract

  • Achromatopsia is the scientific name for colorblindness.
  • Characterized by monochromatic vision due to deficient photoreceptors of the retina.
  • There are currently no treatments for colorblindness.
  • Achromatopsia is a congenital condition that is caused by mutations to one or more genes.
  • Gene therapy research has been advancing over the past decade and has shown promising results in Ophthalmology.
  • Colored vision has been restored in test canines and mice using gene therapy. Also, it has partially improved color vision in a sample of test monkeys.
  • Further research is necessary before human gene therapy can be performed



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Figure 1: Comparative color spectrum of what color blind individuals can perceive (right) and the percentage of people who suffer from each condition (left). Deuteranomaly, Protanomaly, Protanopia and Deuteranopia are all forms of red-green color blindness (incomplete achromatopsia). Tritanopia and Tritanomaly are forms of blue-yellow color blindness (incomplete achromatopsia). The last bar shows the monochromatic vision of a patient with complete achromatopsia.
Source: Color, 2009

Introduction


Achromatopsia, also known as colorblindness, is a congenital condition of the nervous system that effects color vision. There are photoreceptors, called rods and cones, in the eye's retina that transmit light frequencies to the brain where it is then converted into colored visuals. A color blind individual does not experience proper light transduction due to deficient cones. Complete achromatopsia patients have monochromatic vision while incomplete achromatopsia patients have difficulty distinguishing between specific colors. In both cases, colorblindness can be determined by an ophthalmologist using simple testing and/or examining the retina. The retina of a colorblind individual is thinner than that of someone with normal vision and often colorblind individuals also suffer from poor visual acuity. The testing options either require the patient to identify numbers in a series of colored dots or to match light intensities of multiple color combinations. Are You Colorblind?


Four genes have been identified as being associated with colorblindness. These genes are CNGB3, CNGA3, GNAT2 and PDE6C, each named after their functional effects and what they encode. All of these genes effect the pigmented proteins of cones, called rhodopsin, in some way. It is mutations to these genes that cause achromatopsia, both complete and incomplete. Gene therapy is a process in which a short DNA sequence is inserted, through the use of vectors, into an existing genome. This allows the existing gene sequence to be adjusted with the goal of establishing normal conditions. For achromatopsia patients, this mean that successful gene therapy would restore photoreceptor and rhodopsin function and therefore would restore colored vision. This would be incredible considering the fact that there is currently no treatment available for people with this congenital condition. Gene therapy studies currently lack the evidence needed to prove the effectiveness and safety of the process which restricts the testing to non-human animals for ethical reasons. As technologies advance and new theories are tested, gene therapy is becoming more widely accepted for treatment of incurable diseases. Further research is necessary before the process becomes acceptable to experiment on humans, but with the current knowledge and consistently new findings in this field of research, the future of treatment for achromatopsia patients is looking upward.
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Figure 2: Variations in the sequence of the CNGA3 gene that can account for achromatopsia.
Source: GeneCard, n.d.



Materials and Methods
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Work Cited