The CNGB3 gene provides instructions for making one part (the beta 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.
Health Conditions Related to Genetic Changes
More than 40 mutations in the CNGB3 gene have been found to cause the vision disorder achromatopsia. These mutations cause 50 to 70 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. Worldwide, the most common mutation that causes this condition deletes a single DNA building block (base pair) from the CNGB3 gene. This mutation can be written as 1148delC.
Complete achromatopsia occurs frequently in Pingelapese islanders, who live on one of the Eastern Caroline Islands of Micronesia. Among the Pingelapese, this condition results from a mutation that changes a single protein building block (amino acid) in the beta subunit. This mutation replaces the amino acid serine with the amino acid phenylalanine at position 435 in the protein (written as Ser435Phe or S435F).
Most CNGB3 gene mutations prevent the production of any functional beta subunit, which alters the structure of CNG channels. The resulting channels are nonfunctional and prevent cones from carrying out phototransduction. Researchers speculate that the 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.
Because these CNG channels are specific to cones, rods are generally unaffected by this disorder.More About This Health Condition
MedlinePlus Genetics provides information about Cone-rod dystrophyMore About This Health Condition
Mutations in the CNGB3 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 CNGB3 gene mutations cause achromatopsia and others result in progressive cone dystrophy.
Other Names for This Gene
- cone photoreceptor cGMP-gated cation channel beta-subunit
- cyclic nucleotide-gated cation channel modulatory subunit
Additional Information & Resources
Tests Listed in the Genetic Testing Registry
Scientific Articles on PubMed
Catalog of Genes and Diseases from OMIM
- 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. doi: 10.1136/jmg.2003.011437. No abstract available. Citation on PubMed or Free article on PubMed Central
- Kohl S, Baumann B, Broghammer M, Jagle H, Sieving P, Kellner U, Spegal R, Anastasi M, Zrenner E, Sharpe LT, Wissinger B. Mutations in the CNGB3 gene encoding the beta-subunit of the cone photoreceptor cGMP-gated channel are responsible for achromatopsia (ACHM3) linked to chromosome 8q21. Hum Mol Genet. 2000 Sep 1;9(14):2107-16. doi: 10.1093/hmg/9.14.2107. Citation on PubMed
- Kohl S, Jagle H, Wissinger B, Zobor D. Achromatopsia. 2004 Jun 24 [updated 2018 Sep 20]. In: Adam MP, Feldman J, Mirzaa GM, Pagon RA, Wallace SE, Bean LJH, Gripp KW, Amemiya A, editors. GeneReviews(R) [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2023. Available from http://www.ncbi.nlm.nih.gov/books/NBK1418/ Citation on PubMed
- Kohl S, Varsanyi B, Antunes GA, Baumann B, Hoyng CB, Jagle H, Rosenberg T, Kellner U, Lorenz B, Salati R, Jurklies B, Farkas A, Andreasson S, Weleber RG, Jacobson SG, Rudolph G, Castellan C, Dollfus H, Legius E, Anastasi M, Bitoun P, Lev D, Sieving PA, Munier FL, Zrenner E, Sharpe LT, Cremers FP, Wissinger B. CNGB3 mutations account for 50% of all cases with autosomal recessive achromatopsia. Eur J Hum Genet. 2005 Mar;13(3):302-8. doi: 10.1038/sj.ejhg.5201269. Citation on PubMed
- Michaelides M, Aligianis IA, Ainsworth JR, Good P, Mollon JD, Maher ER, Moore AT, Hunt DM. Progressive cone dystrophy associated with mutation in CNGB3. Invest Ophthalmol Vis Sci. 2004 Jun;45(6):1975-82. doi: 10.1167/iovs.03-0898. 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. doi: 10.1038/77162. Citation on PubMed
- 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. Citation on PubMed
- Wiszniewski W, Lewis RA, Lupski JR. Achromatopsia: the CNGB3 p.T383fsX mutation results from a founder effect and is responsible for the visual phenotype in the original report of uniparental disomy 14. Hum Genet. 2007 May;121(3-4):433-9. doi: 10.1007/s00439-006-0314-y. Epub 2007 Jan 31. Citation on PubMed