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RLBP1
retinaldehyde binding protein 1
RLBP1 is located on the long (q) arm of chromosome 15, at band 15q26.1. Arm ratio per GRCh38 - banding schematic.
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Overview
RLBP1 encodes retinaldehyde binding protein 1, a small intracellular protein that functions within the visual cycle of the retina. The visual cycle is a series of biochemical reactions that regenerate the light-sensitive molecule 11-cis-retinal, which is required for phototransduction in rod and cone photoreceptor cells. This protein acts as a carrier for retinoids, moving them between different retinal cell types to ensure continuous visual function.
Pathogenic variants in RLBP1 can impair the efficient recycling of retinoids, leading to progressive degeneration of the retina. The gene is included on NHS clinical panels for retinal disorders, reflecting its importance in inherited eye conditions. Understanding RLBP1 function helps explain the molecular basis of certain forms of inherited vision loss.
What the gene does
Retinaldehyde binding protein 1 serves as an intracellular carrier for 11-cis-retinaldehyde and 11-cis-retinol, two forms of vitamin A that are critical intermediates in the visual cycle. After light exposure bleaches the visual pigment rhodopsin in photoreceptor cells, all-trans-retinal is released and must be converted back to 11-cis-retinal to restore light sensitivity. This conversion occurs through a series of enzymatic steps involving both photoreceptor cells and the adjacent retinal pigment epithelium.
The protein facilitates the movement of retinoids between these cellular compartments, protecting the hydrophobic retinoid molecules from the aqueous cellular environment whilst delivering them to the appropriate enzymes for processing. By binding retinaldehyde, the protein also prevents non-specific reactions that could generate toxic byproducts. This chaperoning function ensures that the visual cycle operates efficiently, maintaining the continuous supply of 11-cis-retinal needed for vision under varying light conditions. The protein is particularly abundant in the retinal pigment epithelium and in Müller glial cells, which provide metabolic support to photoreceptors.
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Chromosome location
RLBP1 is located on chromosome 15 at position 15q26.1, near the end of the long arm of the chromosome. This chromosomal region contains several genes involved in various metabolic and regulatory functions. The specific genomic context of RLBP1 at this location has been mapped through human genome sequencing efforts, allowing precise identification of variants within the gene.
Protein structure
The retinaldehyde binding protein 1 is composed of 317 amino acids and contains a CRAL-TRIO domain spanning amino acids 136 to 297. This domain is characteristic of proteins that bind small lipophilic molecules and is found in several retinoid- and tocopherol-binding proteins. The CRAL-TRIO domain forms a hydrophobic pocket that accommodates the retinaldehyde molecule, shielding it from the surrounding aqueous environment whilst allowing controlled release to target enzymes. The three-dimensional structure of this domain enables the protein to discriminate between different retinoid isomers, ensuring specificity in the visual cycle.
Key variants
Pathogenic variants in RLBP1 can disrupt the protein's ability to bind or transport retinoids effectively, leading to impaired visual cycle function. These variants may affect the stability of the protein, alter the binding pocket of the CRAL-TRIO domain, or interfere with protein folding. Both missense variants, which change single amino acids, and truncating variants, which produce shortened proteins, have been identified in affected individuals. The clinical consequences of RLBP1 variants typically manifest as progressive retinal degeneration.
No pathogenic or likely-pathogenic ClinVar variants recorded yet for this gene.
Associated conditions
Variants in RLBP1 are associated with inherited retinal disorders that present with night blindness and progressive vision loss. The specific pattern of retinal involvement and the age of onset can vary depending on the nature of the genetic variants and other modifying factors. These conditions are characterised by abnormalities in retinal structure and function that can be detected through clinical examination, imaging, and electrodiagnostic testing. Genetic testing for RLBP1 variants forms part of the diagnostic pathway for individuals with unexplained retinal disease.
No disease links recorded for this gene in our reference set.
UK clinical status
Within the NHS Genomic Medicine Service, RLBP1 is included on the Retinal disorders panel (panel R32) with a green classification, indicating strong evidence supporting its role in inherited retinal conditions. This classification means that RLBP1 is analysed as part of genomic testing for patients presenting with features of retinal disease through NHS clinical genetics services. The panel is regularly reviewed to ensure it reflects current evidence and best practice in clinical genomics.
Sources: NHS GMS PanelApp · Genomics England PanelApp · NHS National Genomic Test Directory
Frequently asked questions
What does the RLBP1 protein do in the eye?
The RLBP1 protein transports vitamin A derivatives called retinoids within the retina, ensuring the continuous regeneration of the light-sensitive molecule needed for vision. It acts as a protective carrier, moving retinoids between photoreceptor cells and supporting retinal cells.
How are RLBP1 variants inherited?
RLBP1-related conditions can follow different inheritance patterns depending on the specific variant and phenotype. Genetic counselling can help families understand the inheritance pattern relevant to their situation and the implications for future generations.
Is genetic testing for RLBP1 available on the NHS?
Yes, RLBP1 is included on the NHS Retinal disorders genomic test panel. Testing is available through clinical genetics services for individuals meeting specific clinical criteria, typically coordinated by ophthalmologists or clinical geneticists.