Fundus albipunctatus: review of the literature and report of a novel RDH5 gene mutation affecting the invariant tyrosine (p.Tyr175Phe)

Definition of the transcriptional units of inherited retinal disease genes by meta-analysis of human retinal transcriptome data

BACKGROUND

Inherited retinal diseases (IRD) are genetically heterogeneous disorders that cause the dysfunction or loss of photoreceptor cells and ultimately lead to blindness. To date, next-generation sequencing procedures fail to detect pathogenic sequence variants in coding regions of known IRD disease genes in about 30-40% of patients. One of the possible explanations for this missing heritability is the presence of yet unidentified transcripts of known IRD genes. Here, we aimed to define the transcript composition of IRD genes in the human retina by a meta-analysis of publicly available RNA-seq datasets using an ad-hoc designed pipeline.

RESULTS

We analysed 218 IRD genes and identified 5,054 transcripts, 3,367 of which were not previously reported. We assessed their putative expression levels and focused our attention on 435 transcripts predicted to account for at least 5% of the expression of the corresponding gene. We looked at the possible impact of the newly identified transcripts at the protein level and experimentally validated a subset of them.

CONCLUSIONS

This study provides an unprecedented, detailed overview of the complexity of the human retinal transcriptome that can be instrumental in contributing to the resolution of some cases of missing heritability in IRD patients.

A Novel Pathogenic Variant in the RDH5 Gene in a Patient with Fundus Albipunctatus and Severe Macular Atrophy

Purpose

To report a novel 11-cis retinol dehydrogenase gene (RDH5) variant discovered in a 57-year-old male with fundus albipunctatus (FA) complicated by severe macular atrophy.

Methods

The patient was evaluated with a complete ophthalmic examination, optical coherence tomography (OCT), color fundus photography, green wavelength fundus autofluorescence, visual field testing, full-field ERG (ffERG), and multifocal ERG (mfERG). Genetic analysis investigating gene variants involved in inherited retinal disorders was performed.

Results

The patient presented with a rapid decline in visual acuity and a history of poor night vision. On fundoscopy, he exhibited a phenotype characteristic of FA accompanied by severe macular atrophy bilaterally. Heterozygous variants in the RDH5 gene were identified, including a novel missense variant, c.814_815del (p.Leu272Aspfs^∗63), and a known pathogenic nonsense variant, c.160C > T (p.Arg54^∗). Fundus autofluorescence demonstrated bull's eye maculopathy and hyperautofluorescent perifoveal rings bilaterally. OCT showed foveal atrophy of the outer retina and scattered hyper-reflective lesions in the peripheral macula. The ffERG results showed a severely diminished scotopic and photopic response. The mfERG results demonstrated minimal response in the central macula.

Conclusions

Fundus albipunctatus is a rare, congenital form of stationary night blindness caused almost exclusively by the RDH5 gene. This patient's clinical presentation, diagnostic studies, and genetic testing confirmed the diagnosis of FA. Additionally, he exhibited severe macular atrophy, not typically found in FA. Two RDH5 gene variants were identified, one of which is the novel variant, c.814_815del (p.Leu272Aspfs^∗63). We suggest that this RDH5 genotype may be associated with a more progressive phenotype of FA contributing to macular atrophy.

Novel variants in the RDH5 Gene in a Chinese Han family with fundus albipunctatus

Background

The aim of this study is to identify the genetic defects in a Chinese family with fundus albipunctatus.

Methods

Complete ophthalmic examinations, including slit-lamp biomicroscopy, dilated indirect ophthalmoscopy, fundus photography, autofluorescence, swept source optical coherence tomography (SS-OCT) and full-field electroretinography (ffERG) were performed. Genomic DNA was extracted from blood samples and whole genome sequencing was performed. Variants were validated with Sanger sequencing.

Results

Six members in this Chinese family, including three affected individuals and three controls, were recruited in this study. The ophthalmic examination of three recruited patients was consistent with fundus albipunctatus. Three variants, a novel frameshift deletion c.39delA [p.(Val14CysfsX47] and a haplotype of two rare missense variants, c.683G > A [p.(Arg228Gln)] along with c.710A > G [p.(Tyr237Cys], within the retinal dehydrogenase 5 (RDH5) gene were found to segregate with fundus albipunctatus in this family in an autosomal recessive matter.

Conclusion

We identified novel compound heterozygous variants in RDH5 responsible for fundus albipunctatus in a large Chinese family. The results of our study further broaden the genetic defects of RDH5 associated with fundus albipunctatus.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12886-022-02301-5.

The Role of Vitamin A in Retinal Diseases

Vitamin A is an essential fat-soluble vitamin that occurs in various chemical forms. It is essential for several physiological processes. Either hyper- or hypovitaminosis can be harmful. One of the most important vitamin A functions is its involvement in visual phototransduction, where it serves as the crucial part of photopigment, the first molecule in the process of transforming photons of light into electrical signals. In this process, large quantities of vitamin A in the form of 11-cis-retinal are being isomerized to all-trans-retinal and then quickly recycled back to 11-cis-retinal. Complex machinery of transporters and enzymes is involved in this process (i.e., the visual cycle). Any fault in the machinery may not only reduce the efficiency of visual detection but also cause the accumulation of toxic chemicals in the retina. This review provides a comprehensive overview of diseases that are directly or indirectly connected with vitamin A pathways in the retina. It includes the pathophysiological background and clinical presentation of each disease and summarizes the already existing therapeutic and prospective interventions.

Gene therapy in retinal diseases: A review

Over 2 million people worldwide are suffering from gene-related retinal diseases, inherited or acquired, and over 270 genes have been identified which are found to be responsible for these conditions. This review article touches upon the mechanisms of gene therapy, various enzymes of the visual cycle responsible for different genetic diseases, Luxturna—the first US Food and Drug Administration (FDA)-approved therapeutic gene product, and several ongoing trials of gene therapy for age-related macular degeneration. Gene therapy has tremendous potential for retinal conditions due to its ease of accessibility, immune-privileged status, and tight blood-retinal barriers, limiting systemic side effects of the drug. In recent years, advances in gene therapy in retinal conditions have increasing significantly, with progress in cell-specific targeting and transduction efficiency of gene products through the use of adeno-associated viral vectors (AAVs), suggesting that even greater success in future clinical trials is possible.

The electroretinogram in the genomics era: outer retinal disorders

The inherited retinal diseases (IRDs) have traditionally been described phenotypically with the description evolving to incorporate more sophisticated structural and functional assessments. In the last 25 years there has been considerable advances in the understanding of underlying genetic aetiologies. The role of the ophthalmologist is now to work in a multi-disciplinary team to identify the disease-causing genotype, which might be amenable to gene-directed intervention. Visual electrophysiology is an important tool to assist the ophthalmologist in guiding the clinical geneticist to reach a final molecular diagnosis. This review outlines the physiological basis for the ISCEV standard electrophysiology tests, the role of electrophysiology in localising the functional deficit, correlation with structural findings to guide diagnosis and finally management of IRDs in the era of genomics with emphasis on the outer retina.

Chromosome-level genome assembly of the endangered humphead wrasse Cheilinus undulatus: Insight into the expansion of opsin genes in fishes

Wrasses are dominant components of major coral reef systems. Among wrasses, Cheilinus undulatus is an endangered species with high economic and ecological value that exhibits sex reversal of females to males, while sexual selection occurs in breeding aggregations. However, the molecular-associated mechanism underlying this remains unclear. Opsin gene diversification is regarded as a potent force in sexual selection. Here we present a genome assembly of C. undulatus, using Illumina, Nanopore and Hi-C sequencing. The 1.17 Gb genome was generated from 328 contigs with an N50 length of 16.5 Mb and anchored to 24 chromosomes. In total, 22,218 genes were functionally annotated, and 96.36% of BUSCO genes were fully represented. Transcriptomic analyses showed that 96.79% of the predicted genes were expressed. Transposons were most abundant, accounting for 39.88% of the genome, with low divergence, owing to their evolution with close species ~60.53 million years ago. In total, 567/1,826 gene families were expanded and contracted in the reconstructed phylogeny, respectively. Forty-six genes were under positive selection. Comparative genomic analyses with other fish revealed expansion of opsin SWS2B, LWS1 and Rh2. The elevated duplicates of SWS2B were generated by gene conversions via transposition of transposons followed by nonallelic homologous recombination. Amino acid substitutions of opsin paralogues occurred at key tuning sites, causing a spectral shift in maximal absorbance of visual pigment to capture functional changes. Among these opsin genes, SWS2B-3 and 4 and Rh1 are expressed in the retina. The genome sequence of C. undulatus provides valuable resources for future investigation of the conservation, evolution and behaviour of fishes.

RDH5-Related Fundus Albipunctatus in a Large Japanese Cohort

Purpose

To investigate clinical characteristics of RDH5-related fundus albipunctatus (FAP) in a Japanese cohort.

Methods

Twenty-five patients from 22 pedigrees with RDH5-related FAP were studied. Ophthalmic medical records were reviewed. For genetic analysis, either Sanger sequencing of the RDH5 gene or whole-exome sequencing was performed.

Results

Genetic analysis identified eight different RDH5 variants, including seven known RDH5 variants (p.G35S, p.G107R, p.R167H, p.A240GfsX19, p.R278X, p.R280H, and p.L310delinsEV) and a novel variant: c.259C>T (p.Q87X). The most frequently observed variant was p.L310delinsEV (65.2%, 30/46 alleles). Of 50 eyes examined, 44 eyes (88.0%) showed logMAR best-corrected visual acuity (BCVA) of 0.10 or better. In optical coherence tomography, macular involvement was observed in 12 patients (24 eyes). Ten patients (83.3%) who had good BCVA (0.10 or better) exhibited diffuse disruption of the outer retina with foveal sparing, and two patients (16.7%) exhibited diffuse disruption throughout the macula and decreased BCVA. Among the 24 eyes, ring-or crescent-shaped hyperautofluorescence or irregular autofluorescence around the fovea was observed in 15 eyes (83.3%) of 18 eyes examined by fundus autofluorescence imaging. Full-field electroretinography showed extinguished or severely decreased rod responses in all 23 examined patients, whereas decreased cone responses were seen in 17 patients (73.9%).

Conclusions

Multimodal imaging and electroretinography of RDH5-related FAP revealed high frequencies of macular involvement in older patients and decreased cone responses. Our findings suggest that progressive macular/cone dysfunction, as well as delayed rod function, may be key phenotypic features of RDH5-related FAP.

A novel homozygous frameshift variant in the cellular retinaldehyde-binding protein 1 (RLBP1) gene causes retinitis punctata albescens

BACKGROUND

Retinitis punctata albescens is a form of retinitis pigmentosa characterized by white fleck-like deposits in the fundus, in most cases caused by pathogenic variants in RLBP1 gene. The purpose of this work is to report the phenotypic and genotypic data of a patient with retinitis punctata albescens carrying a deletion in the RLBP1 gene.

RESULTS

An 8-year-old Caucasian female has been complaining of nyctalopia for the last 2 years. No other ocular symptoms were present. No relevant past medical or familiar history was described. At clinical examination, the patient's best-corrected visual acuity was 20/20 in both eyes. Anterior segment evaluation and intraocular pressure were normal in both eyes. At fundoscopy, multiple punctate whitish-yellow fleck-like lesions were observed in the proximity of temporal superior and inferior vascular arcades. Scotopic electroretinogram demonstrated severely reduced rod response, without improvement or recovery of rod system function after prolonged dark adaptation. Blood DNA samples of this patient and from her parents were screened for causal variants in RLBP1, RDH5, and PRPH2.

CONCLUSION

A probable pathogenic frameshift variant was identified in homozygosity in the RLBP1 gene with an autosomal recessive transmission as another cause of retinitis punctata albescens. This DNA variant will aid ongoing functional studies and add to our understanding of the molecular pathology about RLBP1-associated retinopathies.

A spectral-domain optical coherence tomographic analysis of Rdh5-/- mice retina

PURPOSE

To investigate the longitudinal findings of spectral-domain optical coherence tomography (SD-OCT) in relation to the morphologic features in Rdh5 knockout (Rdh5-/-) mice.

MATERIALS AND METHODS

The mouse retina was segmented into four layers; the inner retinal (A), outer plexiform and outer nuclear (B), rod/cone (C), and retinal pigment epithelium (RPE)/choroid (D) layers. The thickness of each retinal layer of Rdh5-/- mice was longitudinally and quantitatively measured at six time points from postnatal months (PM) 1 to PM6 using SD-OCT. Age-matched C57BL/6J mice were employed as wild-type controls. The data were statistically compared using Student's t-test. The fundus appearance was assessed, histologic and ultrastructural examinations were performed in both groups.

RESULTS

Layers A and B were significantly thinner in the Rdh5-/- mice than in the wild-type C57BL/6J mice during the observation periods. Layers C and D became thinner in the Rdh5-/- mice than in the wild-type mice after PM6. Although no abnormalities corresponding to whitish fundus dots were detected by SD-OCT or histologic examinations, the intracellular accumulation of low-density vacuoles was noted in the RPE of the Rdh5-/- mice by electron microscopy. The photoreceptor nuclei appeared less dense in the Rdh5-/- mice than in the wild-type mice.

DISCUSSION

The results from the present study suggest that although it is difficult to detect qualitative abnormalities, SD-OCT can detect quantitative changes in photoreceptors even in the early stage of retinal degeneration induced by the Rdh5 gene mutation in mice.

A founder RDH5 splice site mutation leads to retinitis punctata albescens in two inbred Pakistani kindreds

Background: Retinitis punctate albescens (RPA) is a rare form of retinal dystrophy characterized by congenital stationary night blindness and a characteristic fundus appearance. Missense or nonsense mutations in RDH5 in homozygous or heterozygous state have been implicated in RPA.Material and methods: Two consanguineous Pakistani kindreds with the highly variable manifestation of RPA were studied. Whole-exome sequencing was applied to the index subjects in both families. Sanger sequencing of the candidate RDH5 variant was carried out. Pathogenicity of the detected variant was assessed through bioinformatics tools.Results: The ophthalmic examination through full-field electroretinogram of affected patients in both families was consistent with RPA. A novel splice donor variant at the first exon/intron boundary of RDH5 (NM_002905.3: c.-33 + 2dup) segregated in recessive fashion with the clinical phenotype in both families. One of the heterozygous variant carriers was also observed to have a milder expression of retinal flecks. Haplotype analysis surrounding the splice variant and pattern of runs of homozygosity were suggestive of common ancestry in these families.Conclusion: This is the first report of any pathogenic splice variant at first exon/intron boundary implicated in RPA and suggests another mechanism through which RDH5 variants could be associated with eye phenotype. This study also highlights the importance of a thorough phenotypic evaluation of heterozygous mutation carriers who may exhibit milder symptoms.

Retinal dehydrogenase 5 (RHD5) attenuates metastasis via regulating HIPPO/YAP signaling pathway in Hepatocellular Carcinoma

Retinal dehydrogenase 5 (RDH5) is an important enzyme in the visual cycle. Several studies have reported that the RDH family may play crucial roles in tumor prognosis. However, the role of RDH5 in tumor prognosis is still unclear. We examined the mRNA level of RDH5 by using q-PCR in hepatocellular carcinoma (HCC) and adjacent non-cancerous tissues. The proliferation rate of HCC cells was detected by MTS assay, and the invasive ability was examined by transwell and scratch wound assays. The YAP protein localization and expression were visualized by immunofluorescence in two different cell lines. CpG islands in the promoter region were predicted by using the methprimer database. Clinical characteristics of a patient cohort data came from The Cancer Genome Atlas database. RDH5 was significantly downregulated in hepatocellular carcinoma tissues, and low RDH5 expression was associated with metastasis and poor patient prognosis. Functional assays revealed that the RDH5 promoter is methylated in HCC cell lines. Moreover, overexpressing RDH5 can suppress metastasis by reversing the epithelial-mesenchymal transition (EMT) process, and RDH5 also inhibits cell proliferation in HCC cell lines. Furthermore, suppressing RDH5 can activate the Hippo/YAP signaling pathway and promote the nuclear translocation of YAP. Clinical data demonstrated that RDH5 is an independent prognostic factor in HCC. In our study, we provided the first evidence that RDH5 plays a crucial role in suppressing proliferation and metastasis, and the RDH5 promoter is methylated in hepatocellular carcinoma. And as an important regulator, RDH5 can suppress the Hippo/YAP signaling pathway. Taken together, it revealed that RDH5 might be a potential therapeutic target in HCC patients.

Rhythmic Regulation of Photoreceptor and RPE Genes Important for Vision and Genetically Associated With Severe Retinal Diseases

Purpose

The aim of the present study was to identify candidate genes for mediating daily adjustment of vision.

Methods

Genes important for vision and genetically associated with severe retinal diseases were tested for 24-hour rhythms in transcript levels in neuronal retina, microdissected photoreceptors, photoreceptor-related pinealocytes, and retinal pigment epithelium-choroid (RPE-choroid) complex by using quantitative PCR.

Results

Photoreceptors of wildtype mice display circadian clock-dependent regulation of visual arrestins (Arr1, Arr4) and the visual cycle gene Rdh12, whereas cells of the RPE-choroid exhibit light-dependent regulation of the visual cycle key genes Lrat, Rpe65, and Rdh5. Clock-driven rhythmicity of Arr1, Arr4, and Rdh12 was observed also in rat pinealocytes, to persist in a mouse model of diabetic retinopathy (db/db) and, in the case of Arr1, to be abolished in retinae of mice deficient for dopamine D₄ receptors. Therefore, the expression rhythms appear to be evolutionary conserved, to be unaffected in diabetic retinopathy, and, for Arr1, to require dopamine signaling via dopamine D4 receptors.

Conclusions

The data of the present study suggest that daily adjustment of retinal function combines clock-dependent regulation of genes responsible for phototransduction termination (Arr1, Arr4) and detoxification (Rdh12) in photoreceptors with light-dependent regulation of genes responsible for retinoid recycling (Lrat, Rpe65, and Rdh5) in RPE. Furthermore, they indicate circadian and light-dependent regulation of genes genetically associated with severe retinal diseases.

Potential Mutations in Chinese Pathologic Myopic Patients and Contributions to Phenotype

Purpose

Pathologic myopia is a leading cause of visual impairment in East Asia. The aim of this study was to investigate the potential mutations in Chinese pathologic myopic patients and to analyze the correlations between genotype and clinical phenotype.

Method

One hundred and three patients with pathologic myopia and one hundred and nine unrelated healthy controls were recruited from Zhongshan Ophthalmic Center. Detailed clinical data, including ultra-widefield retinal images, measurements of best-corrected visual acuity, axial length, refractive error and ophthalmic examination results, were obtained. Blood samples were collected for high-throughput DNA targeted sequencing. Based on the screening results, phenotype-genotype correlations were analyzed.

Results

The study included 196 eyes of 103 patients (36 men and 67 women) with an average age of 52.19 (38.92 – 65.46) years, an average refractive error of -11.80 D (-16.38 – -7.22) and a mean axial length of 28.26 mm (25.79 – 30.73). The patients were subdivided into three groups: myopic chorioretinal atrophy (190 eyes of 101 patients), myopic choroidal neovascularization (17 eyes of 15 patients), and myopic traction retinopathy (71 eyes of 61 patients). Systematic analysis of variants in the 255 genes revealed six potential pathogenic mutations: PEX7, OCA2, LRP5 (rs545382, c.1647T>C), TSPAN12 (rs41623, c.765G>T), RDH5 (rs3138142, c.423C>T) and TTC21B (rs80225158, c.2385G>C). OCA2 mutations were primarily observed in patients with myopic traction maculopathy.

Conclusion

Genetic alterations contribute to various clinical characteristics in Chinese pathologic myopic patients. The study may provide new insights into the etiology of pathologic myopia and potential targets for therapeutic interventions.

Structural biology of 11-cis-retinaldehyde production in the classical visual cycle

The vitamin A derivative 11-cis-retinaldehyde plays a pivotal role in vertebrate vision by serving as the chromophore of rod and cone visual pigments. In the initial step of vision, a photon is absorbed by this chromophore resulting in its isomerization to an all-trans state and consequent activation of the visual pigment and phototransduction cascade. Spent chromophore is released from the pigments through hydrolysis. Subsequent photon detection requires the delivery of regenerated 11-cis-retinaldehyde to the visual pigment. This trans-cis conversion is achieved through a process known as the visual cycle. In this review, we will discuss the enzymes, binding proteins and transporters that enable the visual pigment renewal process with a focus on advances made during the past decade in our understanding of their structural biology.

Genetic testing for retinitis punctata albescens/fundus albipunctatus

We studied the scientific literature and disease guidelines in order to summarize the clinical utility of genetic testing for retinitis punctata albescens/fundus albipunctatus (RPA/FA). RPA and FA are reported to have autosomal dominant or autosomal recessive inheritance and are associated with variations in the PRPH2, RHO, RLBP1 and RDH5 genes. There is insufficient data to establish their prevalence. Clinical diagnosis is based on clinical findings, ophthalmological examination, optical coherence tomography, visual field testing and undetectable or severely reduced electroretinogram amplitudes. The genetic test is useful for confirming diagnosis, and for differential diagnosis, couple risk assessment and access to clinical trials.

Measurement of dark adaptometry during ISCEV standard flash electroretinography

PURPOSE

Dark adaptometry (DA) is a sensitive test for diagnosis of retinal disease. Patients requiring flash electroretinograms (ERGs) benefit from DA for proper diagnosis. Our purpose was to develop a DA test to be administered during the 20-min dark adaptation period of the flash ERG ( www.iscev.org ) using alternating red and blue stimuli to bias responses in favor of cones (red) and rods (blue).

METHODS

An ERG Ganzfeld was used to measure DA in 21 normal subjects and 21 patients with retinal disease. Subjects underwent 75 s of preadaptation followed by 20 min of DA using an adaptive staircase to detect alternating flashes of red and blue light. Normative red and blue DA was compared to patients at the 10-min midpoint and 20-min final threshold.

RESULTS

At 15 min, normals and patients showed asymptotic plateaus; hence, final thresholds were achieved within 15 min for parameters of this study. In RP and allied conditions (n = 11), 100% showed significantly elevated blue DA thresholds (> 2SD above normal) at 10 and 20 min. In cone diseases, 80% showed abnormal red DA at 10 min and 30% at 20 min, indicating that delayed adaptation is more typical of cone disease.

CONCLUSIONS

Two-color DA is expediently measured during the DA phase of ERGs providing clinical data which separate rod and cone dysfunction critical for accurate diagnosis of various retinal diseases. It provides an additional benchmark for monitoring function over time and invaluable guidance for patients functioning in dimly lit settings.

Genetic and phenotypic characteristics of four Chinese families with fundus albipunctatus

Fundus albipunctatus (FA) is a rare autosomal recessive form of stationary night blindness characterized by the presence of white or white-yellow dots in the perimacular area and the periphery of the retina, with or without macular involvement. In this study, we examined four Chinese families with FA. Patients were given complete ophthalmic examinations, and blood samples were collected for DNA extraction. Three genes, RDH5, RLBP1 and RPE65, were screened by direct sequencing. Mutations in RDH5 were identified in three families and mutations in RPE65 were identified in one family. This is the second reported case of FA caused by mutations in RPE65.