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Genetics Home Reference: your guide to understanding genetic conditions
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CNGA3

Reviewed January 2015

What is the official name of the CNGA3 gene?

The official name of this gene is “cyclic nucleotide gated channel alpha 3.”

CNGA3 is the gene's official symbol. The CNGA3 gene is also known by other names, listed below.

What is the normal function of the CNGA3 gene?

The CNGA3 gene provides instructions for making one part (the alpha subunit) of the cone photoreceptor cyclic nucleotide-gated (CNG) channel. These channels are found exclusively in light-detecting (photoreceptor) cells called cones, which are located in a specialized tissue at the back of the eye known as the retina. Cones provide vision in bright light (daylight vision), including color vision. Other photoreceptor cells, called rods, provide vision in low light (night vision).

CNG channels are openings in the cell membrane that transport positively charged atoms (cations) into cells. In cones, CNG channels remain open under dark conditions, allowing cations to flow in. When light enters the eye, it triggers the closure of these channels, stopping the inward flow of cations. This change in cation transport alters the cone's electrical charge, which ultimately generates a signal that is interpreted by the brain as vision. This process of translating light into an electrical signal is called phototransduction.

Does the CNGA3 gene share characteristics with other genes?

The CNGA3 gene belongs to a family of genes called CNG (cyclic nucleotide-regulated channels).

A gene family is a group of genes that share important characteristics. Classifying individual genes into families helps researchers describe how genes are related to each other. For more information, see What are gene families? (http://ghr.nlm.nih.gov/handbook/howgeneswork/genefamilies) in the Handbook.

How are changes in the CNGA3 gene related to health conditions?

achromatopsia - caused by mutations in the CNGA3 gene

More than 100 mutations in the CNGA3 gene have been found to cause the vision disorder achromatopsia. These mutations underlie about 25 percent of cases of complete achromatopsia, a form of the disorder characterized by a total lack of color vision and other vision problems that are present from early infancy. CNGA3 gene mutations have also been identified in a few individuals with incomplete achromatopsia, a milder form of the disorder associated with limited color vision.

The CNGA3 gene mutations that underlie complete achromatopsia affect the production or function of the alpha subunit. In some cases, no protein is produced. In others, the protein is altered and does not function normally. CNG channels assembled without the alpha subunit or with an abnormal subunit are nonfunctional; they prevent cones from carrying out phototransduction. Researchers speculate that some defective channels allow a huge influx of cations into cones, which ultimately causes these cells to self-destruct (undergo apoptosis). A loss of cone function underlies the lack of color vision and other vision problems in people with complete achromatopsia.

A few mutations in the CNGA3 gene reduce but do not eliminate the function of CNG channels in cones. These mutations cause incomplete achromatopsia because the partially functioning cones can transmit some visual information to the brain.

Because these CNG channels are specific to cones, rods are generally unaffected by this disorder.

other disorders - caused by mutations in the CNGA3 gene

Mutations in the CNGA3 gene have also been identified in a small percentage of cases of progressive cone dystrophy. Like achromatopsia (described above), this condition affects the function of cones in the retina. However, unlike achromatopsia, progressive cone dystrophy is associated with cones that work normally at birth but begin to malfunction in childhood or adolescence. Over time, people with progressive cone dystrophy develop increasing blurriness and loss of color vision. It is unclear why some CNGA3 gene mutations cause achromatopsia and others result in progressive cone dystrophy.

Where is the CNGA3 gene located?

Cytogenetic Location: 2q11.2

Molecular Location on chromosome 2: base pairs 98,346,154 to 98,398,600

The CNGA3 gene is located on the long (q) arm of chromosome 2 at position 11.2.

The CNGA3 gene is located on the long (q) arm of chromosome 2 at position 11.2.

More precisely, the CNGA3 gene is located from base pair 98,346,154 to base pair 98,398,600 on chromosome 2.

See How do geneticists indicate the location of a gene? (http://ghr.nlm.nih.gov/handbook/howgeneswork/genelocation) in the Handbook.

Where can I find additional information about CNGA3?

You and your healthcare professional may find the following resources about CNGA3 helpful.

You may also be interested in these resources, which are designed for genetics professionals and researchers.

What other names do people use for the CNGA3 gene or gene products?

  • ACHM2
  • CCNC1
  • CCNCa
  • CCNCalpha
  • CNCG3
  • CNG3
  • CNGA3_HUMAN
  • cone photoreceptor cGMP-gated channel alpha subunit

See How are genetic conditions and genes named? (http://ghr.nlm.nih.gov/handbook/mutationsanddisorders/naming) in the Handbook.

What glossary definitions help with understanding CNGA3?

achromatopsia ; apoptosis ; cation ; cell ; cell membrane ; channel ; cones ; gene ; nucleotide ; photoreceptor ; protein ; retina ; rods ; subunit ; tissue

You may find definitions for these and many other terms in the Genetics Home Reference Glossary (http://ghr.nlm.nih.gov/glossary).

References

  • Gene Review: Achromatopsia (http://www.ncbi.nlm.nih.gov/books/NBK1418)
  • Johnson S, Michaelides M, Aligianis IA, Ainsworth JR, Mollon JD, Maher ER, Moore AT, Hunt DM. Achromatopsia caused by novel mutations in both CNGA3 and CNGB3. J Med Genet. 2004 Feb;41(2):e20. (http://www.ncbi.nlm.nih.gov/pubmed/14757870?dopt=Abstract)
  • Koeppen K, Reuter P, Ladewig T, Kohl S, Baumann B, Jacobson SG, Plomp AS, Hamel CP, Janecke AR, Wissinger B. Dissecting the pathogenic mechanisms of mutations in the pore region of the human cone photoreceptor cyclic nucleotide-gated channel. Hum Mutat. 2010 Jul;31(7):830-9. doi: 10.1002/humu.21283. (http://www.ncbi.nlm.nih.gov/pubmed/20506298?dopt=Abstract)
  • 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. (http://www.ncbi.nlm.nih.gov/pubmed/9662398?dopt=Abstract)
  • NCBI Gene (http://www.ncbi.nlm.nih.gov/gene/1261)
  • Patel KA, Bartoli KM, Fandino RA, Ngatchou AN, Woch G, Carey J, Tanaka JC. Transmembrane S1 mutations in CNGA3 from achromatopsia 2 patients cause loss of function and impaired cellular trafficking of the cone CNG channel. Invest Ophthalmol Vis Sci. 2005 Jul;46(7):2282-90. (http://www.ncbi.nlm.nih.gov/pubmed/15980212?dopt=Abstract)
  • Reuter P, Koeppen K, Ladewig T, Kohl S, Baumann B, Wissinger B; Achromatopsia Clinical Study Group. Mutations in CNGA3 impair trafficking or function of cone cyclic nucleotide-gated channels, resulting in achromatopsia. Hum Mutat. 2008 Oct;29(10):1228-36. doi: 10.1002/humu.20790. (http://www.ncbi.nlm.nih.gov/pubmed/18521937?dopt=Abstract)
  • Thiadens AA, Roosing S, Collin RW, van Moll-Ramirez N, van Lith-Verhoeven JJ, van Schooneveld MJ, den Hollander AI, van den Born LI, Hoyng CB, Cremers FP, Klaver CC. Comprehensive analysis of the achromatopsia genes CNGA3 and CNGB3 in progressive cone dystrophy. Ophthalmology. 2010 Apr;117(4):825-30.e1. doi: 10.1016/j.ophtha.2009.09.008. Epub 2010 Jan 15. (http://www.ncbi.nlm.nih.gov/pubmed/20079539?dopt=Abstract)
  • Tränkner D, Jägle H, Kohl S, Apfelstedt-Sylla E, Sharpe LT, Kaupp UB, Zrenner E, Seifert R, Wissinger B. Molecular basis of an inherited form of incomplete achromatopsia. J Neurosci. 2004 Jan 7;24(1):138-47. (http://www.ncbi.nlm.nih.gov/pubmed/14715947?dopt=Abstract)
  • Wissinger B, Gamer D, Jägle H, Giorda R, Marx T, Mayer S, Tippmann S, Broghammer M, Jurklies B, Rosenberg T, Jacobson SG, Sener EC, Tatlipinar S, Hoyng CB, Castellan C, Bitoun P, Andreasson S, Rudolph G, Kellner U, Lorenz B, Wolff G, Verellen-Dumoulin C, Schwartz M, Cremers FP, Apfelstedt-Sylla E, Zrenner E, Salati R, Sharpe LT, Kohl S. CNGA3 mutations in hereditary cone photoreceptor disorders. Am J Hum Genet. 2001 Oct;69(4):722-37. Epub 2001 Aug 30. (http://www.ncbi.nlm.nih.gov/pubmed/11536077?dopt=Abstract)

 

The resources on this site should not be used as a substitute for professional medical care or advice. Users seeking information about a personal genetic disease, syndrome, or condition should consult with a qualified healthcare professional. See How can I find a genetics professional in my area? (http://ghr.nlm.nih.gov/handbook/consult/findingprofessional) in the Handbook.

 
Reviewed: January 2015
Published: January 27, 2015