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RDH12
retinol dehydrogenase 12
RDH12 is located on the long (q) arm of chromosome 14, at band 14q24.1. Arm ratio per GRCh38 - banding schematic.
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Overview
RDH12 encodes retinol dehydrogenase 12, a member of the short-chain dehydrogenase/reductase enzyme family that functions specifically within the retina. This protein participates in the visual cycle, the biochemical pathway that regenerates light-sensitive pigments in rod and cone photoreceptor cells after light exposure. The enzyme catalyses the oxidation of all-trans-retinol to all-trans-retinal, a key step in maintaining the supply of chromophore necessary for continued vision.
Pathogenic variants in RDH12 represent an important cause of autosomal recessive retinal dystrophy, particularly forms that manifest during early childhood. The gene's specific expression pattern in photoreceptor inner segments reflects its specialised role in retinal vitamin A metabolism, distinguishing it from other retinoid-processing enzymes expressed elsewhere in the eye or body.
What the gene does
The RDH12 protein functions as an NADP-dependent retinol dehydrogenase, catalysing the conversion of all-trans-retinol (vitamin A alcohol) to all-trans-retinal (vitamin A aldehyde) within photoreceptor cells. This enzymatic activity forms part of the retinoid cycle that continuously regenerates 11-cis-retinal, the chromophore that binds to opsin proteins to form light-sensitive visual pigments in rods and cones.
The enzyme shows high substrate specificity for all-trans-retinol and preferentially uses NADP+ as a cofactor. RDH12 localises to the inner segments of photoreceptor cells, positioning it strategically to process retinoids returning from the retinal pigment epithelium. By maintaining appropriate retinoid flux through the visual cycle, the protein helps ensure photoreceptors can respond to repeated light stimulation.
Evidence suggests RDH12 may also play a protective role by reducing accumulation of toxic retinoid byproducts. The enzyme's activity helps prevent the formation of potentially harmful compounds that can damage photoreceptor membranes and contribute to cell degeneration when retinoid metabolism is disrupted.
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Chromosome location
RDH12 is located on the long arm of chromosome 14 at position 24.1, designated cytogenetically as 14q24.1. The gene spans approximately 12 kilobases of genomic DNA and contains six exons that encode the mature messenger RNA transcript. This chromosomal region contains several other genes involved in diverse cellular functions, though RDH12 itself shows highly restricted expression predominantly in retinal tissue.
Protein structure
Domain architecture has not been experimentally characterised in detail for this protein. The RDH12 enzyme comprises 316 amino acids and belongs structurally to the short-chain dehydrogenase/reductase superfamily, characterised by a conserved catalytic mechanism and nucleotide-binding fold. The protein likely adopts the typical SDR architecture featuring a central beta-sheet flanked by alpha-helices, creating the binding pocket for both substrate and cofactor, though specific domain boundaries have not been formally annotated.
Key variants
Pathogenic variants in RDH12 follow an autosomal recessive inheritance pattern, meaning affected individuals typically carry two altered copies of the gene. The variant spectrum includes missense changes, nonsense mutations, small deletions, and splice-site alterations distributed across the coding sequence. Certain populations show recurrent variants due to founder effects, whilst other changes appear to be private to individual families. The functional consequences of pathogenic variants generally involve loss of enzymatic activity or protein instability, compromising the visual cycle.
No pathogenic or likely-pathogenic ClinVar variants recorded yet for this gene.
Associated conditions
Variants in RDH12 cause a spectrum of inherited retinal dystrophies, most commonly presenting as Leber congenital amaurosis or early-onset severe retinal dystrophy. These conditions typically manifest in infancy or early childhood with profound vision impairment, nystagmus (involuntary eye movements), and markedly reduced electrical responses on electroretinography. The retinal degeneration is progressive, though the rate of vision loss varies among affected individuals. Some cases present with a slightly later onset and slower progression, occasionally classified as retinitis pigmentosa depending on clinical features and age at presentation.
No disease links recorded for this gene in our reference set.
UK clinical status
RDH12 is included in the NHS Genomic Medicine Service Retinal Disorders panel with green classification (R32), indicating strong evidence supporting its clinical validity for diagnostic testing in patients with inherited retinal disease. This panel status reflects the gene's well-established role in early-onset retinal dystrophies and supports its use in genomic testing for individuals presenting with relevant clinical features through NHS pathways.
Sources: NHS GMS PanelApp · Genomics England PanelApp · NHS National Genomic Test Directory
Frequently asked questions
What inheritance pattern do RDH12 variants follow?
RDH12-related retinal dystrophies follow an autosomal recessive inheritance pattern. This means an individual must inherit pathogenic variants in both copies of the gene (one from each parent) to develop the condition. Parents who each carry one variant are typically unaffected carriers.
At what age do RDH12-related eye conditions typically appear?
Vision problems associated with RDH12 variants most commonly begin in infancy or early childhood, often presenting as Leber congenital amaurosis or early-onset severe retinal dystrophy. Some individuals experience a slightly later onset with features more consistent with retinitis pigmentosa, though early childhood presentation is most characteristic.
How does RDH12 relate to vitamin A?
RDH12 encodes an enzyme that processes vitamin A derivatives (retinoids) within photoreceptor cells as part of the visual cycle. The protein converts retinol to retinal, helping regenerate the light-sensitive pigments necessary for vision. Loss of RDH12 function disrupts this vitamin A metabolism specifically in the retina.