|http://ghr.nlm.nih.gov/ A service of the U.S. National Library of Medicine®|
The official name of this gene is “cyclic nucleotide gated channel beta 3.”
CNGB3 is the gene's official symbol. The CNGB3 gene is also known by other names, listed below.
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.
The CNGB3 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.
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.
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.
Cytogenetic Location: 8q21.3
Molecular Location on chromosome 8: base pairs 86,573,934 to 86,743,674
The CNGB3 gene is located on the long (q) arm of chromosome 8 at position 21.3.
More precisely, the CNGB3 gene is located from base pair 86,573,934 to base pair 86,743,674 on chromosome 8.
See How do geneticists indicate the location of a gene? (http://ghr.nlm.nih.gov/handbook/howgeneswork/genelocation) in the Handbook.
You and your healthcare professional may find the following resources about CNGB3 helpful.
You may also be interested in these resources, which are designed for genetics professionals and researchers.
See How are genetic conditions and genes named? (http://ghr.nlm.nih.gov/handbook/mutationsanddisorders/naming) in the Handbook.
achromatopsia ; amino acid ; apoptosis ; base pair ; cation ; cell ; cell membrane ; channel ; cones ; DNA ; gene ; mutation ; nucleotide ; phenylalanine ; photoreceptor ; protein ; retina ; rods ; serine ; subunit ; tissue
You may find definitions for these and many other terms in the Genetics Home Reference Glossary (http://ghr.nlm.nih.gov/glossary).
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.