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CNGB1
cyclic nucleotide gated channel subunit beta 1
The CNGB1 gene provides instructions for a protein that forms an essential part of cyclic nucleotide-gated (CNG) channels, predominantly found in the photoreceptor cells of the retina, which are crucial for light perception. CNGB1 encodes the beta subunit of a cyclic nucleotide-gated channel.
CNGB1 is located on the long (q) arm of chromosome 16, at band 16q21. Arm ratio per GRCh38 - banding schematic.
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Overview
The CNGB1 gene carries the genetic blueprint for a protein known as the cyclic nucleotide-gated channel subunit beta 1. This protein is a key component of ion channels that are predominantly active in the retina's photoreceptor cells, specifically rod photoreceptors responsible for vision in dim light. These channels are integral to the phototransduction cascade, which allows the eye to detect light and send visual information to the brain.
Dysfunction of the CNGB1 protein can disrupt this crucial process, leading to various inherited retinal diseases. Understanding the role of CNGB1 helps in comprehending the mechanisms behind these conditions and developing potential therapeutic strategies.
What the gene does
The protein produced from the CNGB1 gene is a beta subunit of a cyclic nucleotide-gated (CNG) ion channel. These channels are heteromeric, meaning they are composed of different protein subunits, typically alpha and beta. In photoreceptor cells, CNG channels are responsible for regulating the flow of ions, particularly calcium and sodium, into the cell following light stimulation. This ion flow is a critical step in converting light signals into electrical impulses that the brain can interpret as vision.
The CNGB1 protein itself does not form a functional channel alone but co-assembles with alpha subunits to create a complete, functional channel. It plays a significant role in modulating the channel's properties, including its sensitivity to cyclic guanosine monophosphate (cGMP), which is a key messenger in the phototransduction pathway. The beta subunit also contributes to the channel's trafficking and localisation within the photoreceptor cell, ensuring the channels are correctly positioned to respond to light effectively.
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Chromosome location
The CNGB1 gene is situated on chromosome 16 at band q21. This specifies its precise physical location on the long (q) arm of chromosome 16. The gene consists of multiple exons, which are the coding regions that are ultimately translated into the CNGB1 protein.
Protein structure
The CNGB1 protein is comprised of 1251 amino acids and exhibits a complex modular structure. It features several Disordered regions, including segments at amino acids 1-75, 121-151, 172-252, 314-561, 585-619, and 1151-1251. Distinct functional domains include two Calmodulin-binding regions known as CaM1 (amino acids 557-567) and CaM2 (amino acids 1148-1154). An IQ-like Motif is present from amino acids 568-578. The Ion conduction pathway spans amino acids 786-885, identifying the segment crucial for ion transport. A C-linker region is located between amino acids 888-964, connecting the transmembrane segments to the regulatory domain, which is a Cyclic nucleotide-binding domain from amino acids 968-1084, responsible for binding cGMP.
Key variants
Variants in the CNGB1 gene can occur in various forms, including single nucleotide changes, insertions, and deletions. These genetic alterations can affect the gene's ability to produce a functional CNGB1 protein or alter the protein's structure and activity. The specific impact of a variant often depends on its location within the gene and how it changes the protein's function within the cyclic nucleotide-gated channel.
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.16C>T | p.Gln6Ter | Pathogenic/Likely pathogenic | ★★☆☆ | Retinitis pigmentosa 45 |
c.1730_1731insC | p.Glu577fs | Pathogenic/Likely pathogenic | ★★☆☆ | Retinitis pigmentosa 45 |
c.1977G>A | p.Trp659Ter | Pathogenic/Likely pathogenic | ★★☆☆ | CNGB1-related disorder |
c.2030G>A | p.Arg677His | Pathogenic/Likely pathogenic | ★★☆☆ | CNGB1-related disorder |
c.2225del | p.Leu742fs | Pathogenic/Likely pathogenic | ★★☆☆ | Retinal dystrophy |
c.2305-34G>A | - | Pathogenic/Likely pathogenic | ★★☆☆ | Retinitis pigmentosa 45 |
c.2544del | p.Leu849fs | Pathogenic/Likely pathogenic | ★★☆☆ | Retinitis pigmentosa 45 |
c.2775G>A | p.Trp925Ter | Pathogenic | ★★☆☆ | Retinitis pigmentosa 45 |
c.2977-1G>A | - | Pathogenic/Likely pathogenic | ★★☆☆ | Retinitis pigmentosa 45 |
c.816_819del | p.His273fs | Pathogenic/Likely pathogenic | ★★☆☆ | Retinitis pigmentosa 45 |
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
Pathogenic variants in the CNGB1 gene are primarily associated with inherited retinal disorders. These conditions typically affect the photoreceptor cells, leading to progressive vision loss. The clinical presentation and severity can vary, but generally involve impaired vision, particularly in low light conditions, and can lead to significant visual impairment over time. The specific disease type is often classified based on the pattern of retinal degeneration observed.
No disease links recorded for this gene in our reference set.
UK clinical status
The CNGB1 gene is included in the 'Retinal disorders' panel (R32) within the NHS Genomic Medicine Service, indicated by a 'green' status. This means there is strong evidence supporting the gene's association with these conditions, and it is routinely tested in relevant clinical contexts in the UK.
Sources: NHS GMS PanelApp · Genomics England PanelApp · NHS National Genomic Test Directory
Frequently asked questions
What is the main function of the CNGB1 gene?
The CNGB1 gene provides instructions for a protein that forms a crucial beta subunit of cyclic nucleotide-gated (CNG) ion channels, primarily in the rod photoreceptors of the retina. These channels are essential for converting light into electrical signals, a process known as phototransduction, which enables vision.
Which types of conditions are associated with CNGB1 variants?
Variants in the CNGB1 gene are primarily associated with inherited retinal disorders. These conditions typically involve progressive degeneration of the retina's photoreceptor cells, which can lead to impaired vision and, in some cases, significant visual loss.
Is CNGB1 testing available in the NHS?
Yes, the CNGB1 gene is part of the 'Retinal disorders' panel (R32) offered by the NHS Genomic Medicine Service. This indicates that it is an established gene for testing in appropriate clinical scenarios within the UK.