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CNGB3
cyclic nucleotide gated channel subunit beta 3
The CNGB3 gene provides instructions for a key component of cyclic nucleotide-gated (CNG) channels, which are vital for proper cone photoreceptor function and colour vision in the eye. CNGB3 encodes the beta subunit of CNG channels, found exclusively in the cone photoreceptor cells of the retina.
CNGB3 is located on the long (q) arm of chromosome 8, at band 8q21.3. Arm ratio per GRCh38 - banding schematic.
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Overview
The CNGB3 gene, or cyclic nucleotide gated channel subunit beta 3, contains the genetic blueprint for a crucial part of the cyclic nucleotide-gated (CNG) channel. These channels are predominantly located in the cone photoreceptor cells within the retina of the eye. Cones are responsible for colour vision and visual acuity in bright light conditions.
Changes in the CNGB3 gene are frequently associated with inherited retinal disorders, affecting the ability of these cone cells to function correctly. Understanding CNGB3 is therefore important for diagnosing and researching conditions that impair sight.
What the gene does
The CNGB3 gene directs the production of the beta subunit, an essential component of the cyclic nucleotide-gated (CNG) channel. These specialised ion channels are situated in the cell membranes of cone photoreceptor cells in the retina. CNG channels facilitate the transport of positively charged ions into these cells, a process critical for initiating the visual signal.
In low light conditions, CNG channels generally remain open, allowing ions to flow. However, when light strikes the eye, these channels close, which alters the electrical charge of the cone cell. This change generates an electrical signal that is then transmitted to the brain. This entire mechanism, known as phototransduction, is how light is converted into the visual information we perceive. The CNGB3 subunit is integral to the proper functioning of this intricate visual pathway.
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Chromosome location
The CNGB3 gene is located on chromosome 8, specifically at position 8q21.3. This genomic address specifies the exact location of the gene within the human genome. The gene provides instructions for a protein that is 809 amino acids long.
Protein structure
The CNGB3 protein comprises several distinct functional regions. The N-terminal portion includes disordered regions at amino acids 1-121 and 153-178. Key functional elements include the ion conduction pathway, spanning amino acids 348-447, which is responsible for ion movement across the cell membrane. Within this pathway, the selectivity filter (amino acids 407-410) plays a role in determining which ions can pass through. Further along, a C-linker region (amino acids 450-526) connects to the cyclic nucleotide-binding domain (amino acids 530-646), which is crucial for channel regulation. Another disordered region is found towards the C-terminus, from amino acids 698-776.
Key variants
Genetic changes, often referred to as variants or mutations, within the CNGB3 gene can disrupt the normal function of the CNG channel beta subunit. These variants can lead to a non-functional or improperly functioning protein, thereby impairing the critical process of phototransduction in cone cells. The specific effect of a variant depends on its nature and location within the gene.
Sample of pathogenic variants
10 pathogenic / likely-pathogenic variants from ClinVar, ranked by review status (expert-panel-reviewed first). This is a sample; recurrent founder variants in a specific population may not appear here - see the full ClinVar listing via the link above.
| Variant (HGVS) | Protein change | Classification | Evidence | Associated condition |
|---|---|---|---|---|
c.1250del | p.Leu417fs | Pathogenic/Likely pathogenic | ★★☆☆ | CNGB3-related disorder |
c.1258_1277del | p.Ile420fs | Pathogenic/Likely pathogenic | ★★☆☆ | CNGB3-related disorder |
c.1318C>T | p.Gln440Ter | Pathogenic/Likely pathogenic | ★★☆☆ | Achromatopsia 3 |
c.1574_1575del | p.Leu524_Phe525insTer | Pathogenic | ★★☆☆ | Retinal dystrophy |
c.2105del | p.Lys702fs | Pathogenic | ★★☆☆ | Achromatopsia 3 |
c.2160_2163del | p.Glu722fs | Pathogenic/Likely pathogenic | ★★☆☆ | Achromatopsia 3 |
c.2168del | p.Asn723fs | Pathogenic/Likely pathogenic | ★★☆☆ | Achromatopsia |
c.372_375del | p.Ile124fs | Pathogenic/Likely pathogenic | ★★☆☆ | Achromatopsia 3 |
c.442_446delinsGAAAAT | p.Lys148fs | Pathogenic | ★★☆☆ | Achromatopsia 3 |
c.566G>A | p.Trp189Ter | Pathogenic | ★★☆☆ | not provided |
Evidence stars indicate ClinVar review status. Individual variant interpretation should always be performed by a qualified clinical laboratory - many variants remain classified as Variants of Uncertain Significance (VUS) pending more research.
Associated conditions
Variants in the CNGB3 gene are a common cause of inherited retinal disorders. Most notably, they are strongly associated with Achromatopsia. Achromatopsia is characterised by severe impairment of colour vision and reduced visual acuity, and in some cases, individuals may perceive only black, white, and shades of grey.
UK clinical status
The CNGB3 gene is included in several NHS Genomic Medicine Service national test panels. It is listed on the 'Retinal disorders' panel (R32) and the 'Albinism or congenital nystagmus' panel (R39), both of which are classified as 'green' genes, indicating strong evidence for their role in these conditions.
Sources: NHS GMS PanelApp · Genomics England PanelApp · NHS National Genomic Test Directory
Frequently asked questions
What is the main function of the CNGB3 gene?
The CNGB3 gene provides instructions for making a subunit of the cyclic nucleotide-gated (CNG) channel, which is crucial for how cone photoreceptor cells in the eye detect light and enable colour vision.
What condition is most commonly associated with CNGB3 variants?
Variants in the CNGB3 gene are frequently associated with Achromatopsia, a hereditary retinal disorder characterised by severely impaired or absent colour vision and reduced visual acuity.
Where are CNG channels located in the body?
Cyclic nucleotide-gated channels containing the CNGB3 protein subunit are found exclusively in the cone photoreceptor cells of the retina, which are responsible for vision in bright light and colour perception.
References
- Thiadens AA, Roosing S, Collin RW. Comprehensive analysis of the achromatopsia genes CNGA3 and CNGB3 in progressive cone dystrophy. Ophthalmology. 2010. PMID: 20079539
- 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. Human genetics. 2007. PMID: 17265047
- Kohl S, Varsanyi B, Antunes GA. CNGB3 mutations account for 50% of all cases with autosomal recessive achromatopsia. European journal of human genetics : EJHG. 2005. PMID: 15657609
- Johnson S, Michaelides M, Aligianis IA. Achromatopsia caused by novel mutations in both CNGA3 and CNGB3. Journal of medical genetics. 2004. PMID: 14757870
- Michaelides M, Aligianis IA, Ainsworth JR. Progressive cone dystrophy associated with mutation in CNGB3. Investigative ophthalmology & visual science. 2004. PMID: 15161866
- Sundin OH, Yang JM, Li Y. Genetic basis of total colourblindness among the Pingelapese islanders. Nature genetics. 2000. PMID: 10888875
- Kohl S, Baumann B, Broghammer M. 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. Human molecular genetics. 2000. PMID: 10958649
- Adam MP, Bick S, Mirzaa GM. Achromatopsia. 1993. PMID: 20301591