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Achromatopsia

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Description

Achromatopsia is a condition characterized by a partial or total absence of color vision. People with complete achromatopsia cannot perceive any colors; they see only black, white, and shades of gray. Incomplete achromatopsia is a milder form of the condition that allows some color discrimination.

Achromatopsia also involves other problems with vision, including an increased sensitivity to light and glare (photophobia), involuntary back-and-forth eye movements (nystagmus), and significantly reduced sharpness of vision (low visual acuity). Affected individuals can also have farsightedness (hyperopia) or, less commonly, nearsightedness (myopia). These vision problems develop in the first few months of life.

Achromatopsia is different from the more common forms of color vision deficiency (also called color blindness), in which people can perceive color but have difficulty distinguishing between certain colors, such as red and green.

Frequency

Achromatopsia affects an estimated 1 in 30,000 people worldwide. Complete achromatopsia is more common than incomplete achromatopsia.

Complete achromatopsia occurs frequently among Pingelapese islanders, who live on one of the Eastern Caroline Islands of Micronesia. Between 4 and 10 percent of people in this population have a total absence of color vision.

Causes

Achromatopsia results from changes in one of several genes: CNGA3, CNGB3, GNAT2, PDE6C, or PDE6H. A particular CNGB3 gene mutation underlies the condition in Pingelapese islanders.

Achromatopsia is a disorder of the retina, which is the light-sensitive tissue at the back of the eye. The retina contains two types of light receptor cells, called rods and cones. These cells transmit visual signals from the eye to the brain through a process called phototransduction. Rods provide vision in low light (night vision). Cones provide vision in bright light (daylight vision), including color vision.

Mutations in any of the genes listed above prevent cones from reacting appropriately to light, which interferes with phototransduction. In people with complete achromatopsia, cones are nonfunctional, and vision depends entirely on the activity of rods. The loss of cone function leads to a total lack of color vision and causes the other vision problems. People with incomplete achromatopsia retain some cone function. These individuals have limited color vision, and their other vision problems tend to be less severe.

Some people with achromatopsia do not have identified mutations in any of the known genes. In these individuals, the cause of the disorder is unknown. Other genetic factors that have not been identified likely contribute to this condition.

Inheritance

This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.

Other Names for This Condition

  • achromatism
  • rod monochromatism
  • total color blindness

References

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  • Kohl S, Marx T, Giddings I, Jägle H, Jacobson SG, Apfelstedt-Sylla E, Zrenner E, Sharpe LT, Wissinger B. Total colourblindness is caused by mutations in the gene encoding the alpha-subunit of the cone photoreceptor cGMP-gated cation channel. Nat Genet. 1998 Jul;19(3):257-9. Citation on PubMed
  • Sundin OH, Yang JM, Li Y, Zhu D, Hurd JN, Mitchell TN, Silva ED, Maumenee IH. Genetic basis of total colourblindness among the Pingelapese islanders. Nat Genet. 2000 Jul;25(3):289-93. Citation on PubMed
  • Thiadens AA, den Hollander AI, Roosing S, Nabuurs SB, Zekveld-Vroon RC, Collin RW, De Baere E, Koenekoop RK, van Schooneveld MJ, Strom TM, van Lith-Verhoeven JJ, Lotery AJ, van Moll-Ramirez N, Leroy BP, van den Born LI, Hoyng CB, Cremers FP, Klaver CC. Homozygosity mapping reveals PDE6C mutations in patients with early-onset cone photoreceptor disorders. Am J Hum Genet. 2009 Aug;85(2):240-7. doi: 10.1016/j.ajhg.2009.06.016. Epub 2009 Jul 16. Citation on PubMed or Free article on PubMed Central
  • Thiadens AA, Slingerland NW, Roosing S, van Schooneveld MJ, van Lith-Verhoeven JJ, van Moll-Ramirez N, van den Born LI, Hoyng CB, Cremers FP, Klaver CC. Genetic etiology and clinical consequences of complete and incomplete achromatopsia. Ophthalmology. 2009 Oct;116(10):1984-9.e1. doi: 10.1016/j.ophtha.2009.03.053. Epub 2009 Jul 9. Citation on PubMed
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