Mutations in the peripherin/RDS gene are an important cause of multifocal pattern dystrophy simulating STGD1/fundus flavimaculatus

Mitochondrial retinopathies and optic neuropathies: The impact of retinal imaging on modern understanding of pathogenesis, diagnosis, and management

Advancements in ocular imaging have significantly broadened our comprehension of mitochondrial retinopathies and optic neuropathies by examining the structural and pathological aspects of the retina and optic nerve in these conditions. This article aims to review the prominent imaging characteristics associated with mitochondrial retinopathies and optic neuropathies, aiming to deepen our insight into their pathogenesis and clinical features. Preceding this exploration, the article provides a detailed overview of the crucial genetic and clinical features, which is essential for the proper interpretation of in vivo imaging. More importantly, we will provide a critical analysis on how these imaging modalities could serve as biomarkers for characterization and monitoring, as well as in guiding treatment decisions. However, these imaging methods have limitations, which will be discussed along with potential strategies to mitigate them. Lastly, the article will emphasize the potential advantages and future integration of imaging techniques in evaluating patients with mitochondrial eye disorders, considering the prospects of emerging gene therapies.

Downregulation of rhodopsin is an effective therapeutic strategy in ameliorating peripherin-2-associated inherited retinal disorders

Given the absence of approved treatments for pathogenic variants in Peripherin-2 (PRPH2), it is imperative to identify a universally effective therapeutic target for PRPH2 pathogenic variants. To test the hypothesis that formation of the elongated discs in presence of PRPH2 pathogenic variants is due to the presence of the full complement of rhodopsin in absence of the required amounts of functional PRPH2. Here we demonstrate the therapeutic potential of reducing rhodopsin levels in ameliorating disease phenotype in knockin models for p.Lys154del (c.458-460del) and p.Tyr141Cys (c.422 A > G) in PRPH2. Reducing rhodopsin levels improves physiological function, mitigates the severity of disc abnormalities, and decreases retinal gliosis. Additionally, intravitreal injections of a rhodopsin-specific antisense oligonucleotide successfully enhance the physiological function of photoreceptors and improves the ultrastructure of discs in mutant mice. Presented findings shows that reducing rhodopsin levels is an effective therapeutic strategy for the treatment of inherited retinal degeneration associated with PRPH2 pathogenic variants.

Hyaluronan improves photoreceptor differentiation and maturation in human retinal organoids

Human stem cell-derived organoids enable both disease modeling and serve as a source of cells for transplantation. Human retinal organoids are particularly important as a source of human photoreceptors; however, the long differentiation period required and lack of vascularization in the organoid often results in a necrotic core and death of inner retinal cells before photoreceptors are fully mature. Manipulating the in vitro environment of differentiating retinal organoids through the incorporation of extracellular matrix components could influence retinal development. We investigated the addition of hyaluronan (HA), a component of the interphotoreceptor matrix, as an additive to promote long-term organoid survival and enhance retinal maturation. HA treatment had a significant reduction in the proportion of proliferating (Ki67+) cells and increase in the proportion of photoreceptors (CRX+), suggesting that HA accelerated photoreceptor commitment in vitro. HA significantly upregulated genes specific to photoreceptor maturation and outer segment development. Interestingly, prolonged HA-treatment significantly decreased the length of the brush border layer compared to those in control retinal organoids, where the photoreceptor outer segments reside; however, HA-treated organoids also had more mature outer segments with organized discs structures, as revealed by transmission electron microscopy. The brush border layer length was inversely proportional to the molar mass and viscosity of the hyaluronan added. This is the first study to investigate the role of exogenous HA, viscosity, and polymer molar mass on photoreceptor maturation, emphasizing the importance of material properties on organoid culture. STATEMENT OF SIGNIFICANCE: Retinal organoids are a powerful tool to study retinal development in vitro, though like many other organoid systems, can be highly variable. In this work, Shoichet and colleagues investigated the use of hyaluronan (HA), a native component of the interphotoreceptor matrix, to improve photoreceptor maturation in developing human retinal organoids. HA promoted human photoreceptor differentiation leading to mature outer segments with disc formation and more uniform and healthy retinal organoids. These findings highlight the importance of adding components native to the developing retina to generate more physiologically relevant photoreceptors for cell therapy and in vitro models to drive drug discovery and uncover novel disease mechanisms.

Clinical, Genotypic, and Imaging Characterization of the Spectrum of ABCA4 Retinopathies

PURPOSE

To investigate the clinical and genotypic differences in the spectrum of ABCA4-associated retinopathies (ABCA4Rs).

DESIGN

Observational, cross sectional case series.

PARTICIPANTS

Sixty-six patients (132 eyes) carrying biallelic ABCA4 variants.

METHODS

Patients underwent visual acuity measurement and multimodal imaging. Clinical records were reviewed for age at onset, presenting symptoms, genetic variants, and electroretinogram (ERG). Each eye was assigned to a phenotype based on age at onset, imaging and ERG: cone dystrophy-bull's-eye maculopathy (CD-BEM, 40 eyes), cone-rod dystrophy (CRD, 12 eyes), Stargardt disease (SD, 28 eyes), late-onset SD (LO-SD, 38 eyes), and fundus flavimaculatus (14 eyes). Images were analyzed for: peripapillary sparing, retinal pigment epithelium (RPE) atrophy (definitely decreased autofluorescence, DDAF), flecks patterns using autofluorescence; type of atrophy according to Classification of Atrophy Meeting reports, macular and choroidal thickness on OCT; and choriocapillaris flow deficits on OCT angiography.

MAIN OUTCOME MEASURES

Primary outcome was to report the demographic, genotypic, and imaging characteristics of the different ABCA4R phenotypes. Secondary objectives included the assessment of imaging biomarkers as outcome measures for clinical trials.

RESULTS

Age at onset was lower in CRD (12 ± 8 years) and higher in patients with LO-SD (59 ± 9 years) (all P < 0.01). Central vision loss was a common presenting symptom in CD-BEM and SD, whereas patients with LO-SD primarily complained of difficult dark adaptation. Missense variants were more frequent in CD-BEM, and splice site in CRD and LO-SD (P < 0.05). Peripapillary sparing was absent in 3 eyes with LO-SD (8%). Cone dystrophy-bull's-eye maculopathy eyes typically had complete outer retinal atrophy alterations (98%), whereas CRD and SD eyes showed both complete outer retinal atrophy and complete RPE and outer retinal atrophy (cRORA) (71%-100%). Patients with LO-SD had larger areas of DDAF (100% cRORA) and of choriocapillaris flow deficits (all P < 0.01). Repeatability of DDAF measurements was low for some phenotypes (CD-BEM and CRD) and atrophic areas <7.5 mm2. Resorbed flecks were significantly associated with CRD and LO-SD (P < 0.01).

CONCLUSIONS

This research provides a thorough evaluation of the spectrum of ABCA4R. Our findings suggest that certain phenotypes show preferential photoreceptor degeneration (e.g., CD-BEM), whereas others have substantial RPE and choriocapillaris alterations (e.g., LO-SD). We recommend that clinical trial end points take into consideration these imaging features to improve the interpretation of their results.

FINANCIAL DISCLOSURE(S)

Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Retinal Dystrophies Associated With Peripherin-2: Genetic Spectrum and Novel Clinical Observations in 241 Patients

Purpose

To describe the clinical, electrophysiological and genetic spectrum of inherited retinal diseases associated with variants in the PRPH2 gene.

Methods

A total of 241 patients from 168 families across 15 sites in 9 countries with pathogenic or likely pathogenic variants in PRPH2 were included. Records were reviewed for age at symptom onset, visual acuity, full-field ERG, fundus colour photography, fundus autofluorescence (FAF), and SD-OCT. Images were graded into six phenotypes. Statistical analyses were performed to determine genotype-phenotype correlations.

Results

The median age at symptom onset was 40 years (range, 4-78 years). FAF phenotypes included normal (5%), butterfly pattern dystrophy, or vitelliform macular dystrophy (11%), central areolar choroidal dystrophy (28%), pseudo-Stargardt pattern dystrophy (41%), and retinitis pigmentosa (25%). Symptom onset was earlier in retinitis pigmentosa as compared with pseudo-Stargardt pattern dystrophy (34 vs 44 years; P = 0.004). The median visual acuity was 0.18 logMAR (interquartile range, 0-0.54 logMAR) and 0.18 logMAR (interquartile range 0-0.42 logMAR) in the right and left eyes, respectively. ERG showed a significantly reduced amplitude across all components (P < 0.001) and a peak time delay in the light-adapted 30-Hz flicker and single-flash b-wave (P < 0.001). Twenty-two variants were novel. The central areolar choroidal dystrophy phenotype was associated with 13 missense variants. The remaining variants showed marked phenotypic variability.

Conclusions

We described six distinct FAF phenotypes associated with variants in the PRPH2 gene. One FAF phenotype may have multiple ERG phenotypes, demonstrating a discordance between structure and function. Given the vast spectrum of PRPH2 disease our findings are useful for future clinical trials.

PRPH2-Related Retinal Dystrophies: Mutational Spectrum in 103 Families from a Spanish Cohort

PRPH2, one of the most frequently inherited retinal dystrophy (IRD)-causing genes, implies a high phenotypic variability. This study aims to analyze the PRPH2 mutational spectrum in one of the largest cohorts worldwide, and to describe novel pathogenic variants and genotype-phenotype correlations. A study of 220 patients from 103 families recruited from a database of 5000 families. A molecular diagnosis was performed using classical molecular approaches and next-generation sequencing. Common haplotypes were ascertained by analyzing single-nucleotide polymorphisms. We identified 56 variants, including 11 novel variants. Most of them were missense variants (64%) and were located in the D2-loop protein domain (77%). The most frequently occurring variants were p.Gly167Ser, p.Gly208Asp and p.Pro221_Cys222del. Haplotype analysis revealed a shared region in families carrying p.Leu41Pro or p.Pro221_Cys222del. Patients with retinitis pigmentosa presented an earlier disease onset. We describe the largest cohort of IRD families associated with PRPH2 from a single center. Most variants were located in the D2-loop domain, highlighting its importance in interacting with other proteins. Our work suggests a likely founder effect for the variants p.Leu41Pro and p.Pro221_Cys222del in our Spanish cohort. Phenotypes with a primary rod alteration presented more severe affectation. Finally, the high phenotypic variability in PRPH2 hinders the possibility of drawing genotype-phenotype correlations.

LONG-TERM FOLLOW-UP OF PRPH2 -ASSOCIATED RETINAL DYSTROPHY

PURPOSE

To report a 13-year follow-up of Peripherin-2 (PRPH2) -associated retinal dystrophy.

METHODS

A 54-year-old female patient presented with decreased vision and mild metamorphopsia in both eyes since the age of 40 years. A complete evaluation was performed using multimodal imaging techniques.

RESULTS

At presentation, fundus examination revealed multiple irregular pisciform flecks in the posterior pole sparing the peripapillary area in both eyes, as well as some mildly atrophic zones in the perifoveal area. The mildly atrophic areas evolved and merged into a central atrophic zone in the following 10 years, leading to a decreased vision of <20/400 in both eyes. The genetic molecular diagnosis revealed a mutation in PRPH2/RDS gene (NM_000322.4:c.421T>C ( p .Tyr141His)). Based on genetics, imaging, and clinical findings, a diagnosis of multifocal pattern dystrophy simulating Stargardt disease 1/fundus flavimaculatus was evoked. Her mother was found to have the same gene mutation, with multiple irregular pisciform flecks in the posterior pole associated with central areolar choroidal dystrophy.

CONCLUSION

This report demonstrated the 13-year progression of multifocal pattern dystrophy simulating Stargardt disease 1/fundus flavimaculatus in a patient with a pathogenic variant of the PRPH2/RDS gene (NM_000322.4:c.421T>C ( p .Tyr141His)).

Analysis of the Outer Retinal Bands in ABCA4 and PRPH2-Associated Retinopathy using OCT

PURPOSE

To evaluate the outer retinal bands using OCT in ABCA4- and PRPH2-associated retinopathy and develop a novel imaging biomarker to differentiate between these 2 genotypes.

DESIGN

Multicenter case-control study.

PARTICIPANTS

Patients with a clinical and genetic diagnosis of ABCA4- or PRPH2-associated retinopathy and an age-matched control group.

METHODS

Macular OCT was used to measure the thickness of the outer retinal bands 2 and 4 by 2 independent examiners at 4 retinal loci.

MAIN OUTCOME MEASURES

Outcome measures included the thicknesses of band 2, band 4, and the band 2/band 4 ratio. Linear mixed modeling was used to make comparisons across the 3 groups. Receiver operating characteristic (ROC) analysis determined the optimal cutoff for the band 2/band 4 ratio to distinguish PRPH2- from ABCA4-associated retinopathy.

RESULTS

We included 45 patients with ABCA4 variants, 45 patients with PRPH2 variants, and 45 healthy controls. Band 2 was significantly thicker in patients with PRPH2 compared with ABCA4 (21.4 vs. 15.9 μm, P < 0.001) variants, whereas band 4 was thicker in patients with ABCA4 variants than those with PRPH2 variants (27.5 vs. 21.7 μm, P < 0.001). Similarly, the band 2/band 4 ratio was significantly different (1.0 vs. 0.6 for PRPH2 vs. ABCA4, P < 0.001). The area under the ROC curve was 0.87 for either band 2 (> 18.58 μm) or band 4 (< 26.17 μm) alone and 0.99 (95% confidence interval: 0.97-0.99) for the band 2/band 4 ratio with a cutoff threshold of 0.79, providing 100% specificity.

CONCLUSIONS

We report an altered outer retinal band profile whereby the band 2/band 4 ratio was able to discriminate between PRPH2- and ABCA4-associated retinopathy. This may have future clinic utility in predicting the genotype and provide further insight into the anatomic correlate of band 2.

FINANCIAL DISCLOSURE(S)

Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Primary versus Secondary Elevations in Fundus Autofluorescence

The method of quantitative fundus autofluorescence (qAF) can be used to assess the levels of bisretinoids in retinal pigment epithelium (RPE) cells so as to aid the interpretation and management of a variety of retinal conditions. In this review, we focused on seven retinal diseases to highlight the possible pathways to increased fundus autofluorescence. ABCA4- and RDH12-associated diseases benefit from known mechanisms whereby gene malfunctioning leads to elevated bisretinoid levels in RPE cells. On the other hand, peripherin2/RDS-associated disease (PRPH2/RDS), retinitis pigmentosa (RP), central serous chorioretinopathy (CSC), acute zonal occult outer retinopathy (AZOOR), and ceramide kinase like (CERKL)-associated retinal degeneration all express abnormally high fundus autofluorescence levels without a demonstrated pathophysiological pathway for bisretinoid elevation. We suggest that, while a known link from gene mutation to increased production of bisretinoids (as in ABCA4- and RDH12-associated diseases) causes primary elevation in fundus autofluorescence, a secondary autofluorescence elevation also exists, where an impairment and degeneration of photoreceptor cells by various causes leads to an increase in bisretinoid levels in RPE cells.

Paramacular Choriocapillaris Atrophy

In this paper, a review of a rare case of paramacular choriocapillaris atrophy with a foveal-sparing phenotype is carried out. The 73-year-old patient stated that they had impaired vision and photophobia in both eyes during a regular ophthalmological examination, denying visual field defects and night blindness. A complete ophthalmological examination (best-corrected visual acuity, applanation tonometry, and biomicroscopy of anterior and posterior segments) and diagnostic tests, including fundus autofluorescence, fluorescein angiography, optical coherence tomography with angiography, computerized perimetry, and electroretinography, were carried out. The underlying genetic pattern is unclear, which points to paramacular choriocapillaris atrophy. According to recent research on histology, pathologies categorized as regional choroidal dystrophies are caused by alterations at the level of the retinal pigment epithelium. Despite the unresolved etiopathogenetic mechanism of foveal sparing in central choroidal and retinal dystrophies, a highly variable disease phenotype with spared fovea and central visual acuity present in a variety of heterogeneous dystrophies supports a disease-independent mechanism that allows the survival of foveal cones. The related preservation of BCVA has implications for individual prognosis and influences how treatment trials for choroidal and retinal dystrophies are designed.

Comparative study of PRPH2 D2 loop mutants reveals divergent disease mechanism in rods and cones

Mutations in the photoreceptor-specific tetraspanin gene peripherin-2 (PRPH2) lead to widely varying forms of retinal degeneration ranging from retinitis pigmentosa to macular dystrophy. Both inter- and intra-familial phenotypic heterogeneity has led to much interest in uncovering the complex pathogenic mechanisms of PRPH2-associated disease. Majority of disease-causing mutations in PRPH2 reside in the second intradiscal loop, wherein seven cysteines control protein folding and oligomerization. Here, we utilize knockin models to evaluate the role of three D2 loop cysteine mutants (Y141C, C213Y and C150S), alone or in combination. We elucidated how these mutations affect PRPH2 properties, including oligomerization and subcellular localization, and contribute to disease processes. Results from our structural, functional and molecular studies revealed that, in contrast to our understanding from prior investigations, rods are highly affected by PRPH2 mutations interfering with oligomerization and not merely by the haploinsufficiency associated with these mutations. On the other hand, cones are less affected by the toxicity of the mutant protein and significantly reduced protein levels, suggesting that knockdown therapeutic strategies may sustain cone functionality for a longer period. This observation provides useful data to guide and simplify the current development of effective therapeutic approaches for PRPH2-associated diseases that combine knockdown with high levels of gene supplementation needed to generate prolonged rod improvement.

NOVEL PRPH2/RDS MUTATION IDENTIFIED IN A FAMILY WITH VARYING CLINICAL MANIFESTATIONS: A CASE REPORT

PURPOSE

To present the case of a family with a novel PRPH2/RDS mutation.

METHODS

A case report of a 44-year-old woman and her immediate family, including the father and a sister who shared her PRPH2/RDS mutation.

RESULTS

A 44-year-old woman presented with examination findings consistent with a butterfly-type pattern dystrophy. A sister had a similar butterfly-type dystrophy, whereas their father had a severe cone-rod dystrophy. Genetic testing revealed the same novel PRPH2/RDS mutation in all three affected individuals, suggesting that this single mutation can produce at least two disparate retinal disease phenotypes.

CONCLUSION

This case describes a novel p.Y225X nonsense mutation in the PRPH2/RDS gene and demonstrates that it is both pathologic and capable of significant phenotypic variability.

New Insight into the Genotype-Phenotype Correlation of PRPH2-Related Diseases Based on a Large Chinese Cohort and Literature Review

Variants in PRPH2 are a common cause of inherited retinal dystrophies with high genetic and phenotypic heterogeneity. In this study, variants in PRPH2 were selected from in-house exome sequencing data, and all reported PRPH2 variants were evaluated with the assistance of online prediction tools and the comparative validation of large datasets. All variants were classified based on the American College of Medical Genetics and Genomics/Association for Molecular Pathology (ACMG/AMP) guidelines. Individuals with pathogenic or likely pathogenic variants of PRPH2 were confirmed by Sanger sequencing. Clinical characteristics were summarized. Ten pathogenic or likely pathogenic variants of PRPH2 were identified in 14 families. In our cohort, the most frequent variant was p.G305Afs*19, accounting for 33.3% (5/15) of alleles, in contrast to the literature, where p.R172G (11.6%, 119/1028) was the most common variant. Nine in-house families (63.8%) were diagnosed with retinitis pigmentosa (RP), distinct from the phenotypic spectrum in the literature, which shows that RP accounts for 27.9% (283/1013) and macular degeneration is more common (45.2%, 458/1013). Patients carrying missense variants predicted as damaging by all seven prediction tools and absent in the gnomAD database were more likely to develop RP compared to those carrying missense variants predicted as damaging with fewer tools or with more than one allele number in the gnomAD database (p = 0.001). The population-specific genetic and phenotypic spectra of PRPH2 were explored, and novel insight into the genotype–phenotype correlation of PRPH2 was proposed. These findings demonstrated the importance of assessing PRPH2 variants in distinct populations and the value of providing practical suggestions for the genetic interpretation of PRPH2 variants.

Clinical Heterogeneity in Two Siblings Harbouring a Heterozygous PRPH2 Pathogenic Variant

PURPOSE

The aim of the study was to describe the clinical and genetic correlation of a c.469 G>A p.(Asp157Asn) heterozygous pathogenic variant in PRPH2 in two siblings of Italian origin.

PATIENTS AND METHODS

Both patients underwent ophthalmic examination, electrophysiological testing, autofluorescence imaging, and optical coherence tomography (OCT). Screening for pathogenic variants of the obtained DNA from the family members was carried out.

RESULTS

The 52-year-old (♀, index patient) and 50-year-old (♂) siblings had BCVA (OD and OS) of 20/20 and 20/16 (♀) and 20/25 and 20/40 (♂), respectively, and suffered increased sensitivity to glare. Yellow irregular macular deposits, numerous small irregular hypo- and hyperreflective spots at the posterior pole, a patchy loss of photoreceptors, and retinal pigment epithelium (RPE) in the perifoveal region were seen. Electrophysiology showed dysfunction of rods and cones, with more affected cone dysfunction in the index patient, contrary to the generalised rod dysfunction in the brother of the index patient. The clinical, electrophysiological, and multimodal imaging findings of both siblings pointed towards Stargardt retinopathy with heterogenic presentation. The DNA analysis identified an autosomal dominant c.469 G>A p.(Asp157Asn) heterozygous pathogenic variant in PRPH2 associated with autosomal dominant cone-rod dystrophy and rod-cone dystrophy. PRPH2 codes for peripherin-2, a membrane protein that consists of 346 amino acids.

CONCLUSIONS

Our findings confirm a heterogeneity in clinical presentation associated with pathogenic variants in PRPH2. It may follow either an autosomal dominant or an autosomal recessive mode of inheritance and show a very heterogeneous clinical manifestation of retinal degeneration, e.g., autosomal dominant retinitis pigmentosa (♂ sibling; II-3) and autosomal dominant cone-rod dystrophy (index ♀ sibling; II-2), autosomal dominant macular dystrophy, and also autosomal recessive retinitis pigmentosa.

Choroidal neovascularization associated with butterfly-shaped pattern dystrophy - a case report

The pattern dystrophies (PDs) are a group of primarily autosomal dominant inherited macular diseases that cause the deposition of lipofuscin in retinal pigment epithelium (RPE) and may lead to significant vision loss in later life. Patients can develop choroidal neovascularization (CNV) and/ or geographic atrophy (GA) and for this reason they are often misdiagnosed as age-related macular degeneration (AMD). We presented a case of a 66-year-old patient complaining of vision loss in the right eye (RE) for 8 months. At the initial examination, his best corrected visual acuity (BCVA) was 0.6 in the RE. Optical coherence tomography angiography (OCTA), fundus autofluorescence (FAF) and fundus fluorescein angiography (FFA) allowed to diagnose butterfly-shaped PD in both eyes with choroidal neovascularization (CNV) in the RE. The patient was treated with three intravitreal anti-vascular epithelial growth factor (anti-VEGF, ranibizumab) injections during six weeks intervals, which improved and stabilized the BCVA of the RE to 0.7 during the over two-year observation period. Our report contributes to the still limited data regarding CNV associated with butterfly-shaped PDs and the results of treatment with ranibizumab. Abbreviations: AMD = age-related macular degeneration, anti-VEGF = anti-vascular epithelial growth factor, AOFVD = adult-onset foveomacular vitelliform dystrophy, BCVA = best corrected visual acuity, CNV = choroidal neovascularization, FAF = fundus autofluorescence, FFA = fundus fluorescein angiography, GA = geographic atrophy, LE = left eye, MIDD = maternally inherited diabetes and deafness, OCT = optical coherence tomography, OCTA = optical coherence tomography angiography, OU = oculus uterque, both eyes, PD = pattern dystrophy, PDSFF = pattern dystrophy simulating fundus flavimaculatus, PDT = photodynamic therapy, PRPH2 = peripherine-2, RE = right eye, RPE = retinal pigment epithelium, VA = visual acuity.

Electrophysiological Evaluation of Macular Dystrophies

Macular dystrophies are a heterogeneous group of genetic disorders that often severely threatens the bilateral central vision of the affected patient. While advances in molecular genetics have been instrumental in the understanding and diagnosis of these disorders, there remains significant phenotypical variation among patients within any particular subset of macular dystrophies. Electrophysiological testing remains a vital tool not only to characterize vision loss for differential diagnosis but also to understand the pathophysiology of these disorders and to monitor the treatment effect, potentially leading to therapeutic advances. This review summarizes the application of electrophysiological testing in macular dystrophies, including Stargardt disease, bestrophinopathies, X-linked retinoschisis, Sorsby fundus dystrophy, Doyne honeycomb retina dystrophy, autosomal dominant drusen, occult macular dystrophy, North Carolina macular dystrophy, pattern dystrophy, and central areolar choroidal dystrophy.

Stargardt-like Clinical Characteristics and Disease Course Associated with Variants in the WDR19 Gene

Variants in WDR19 (IFT144) have been implicated as another possible cause of Stargardt disease. The purpose of this study was to compare longitudinal multimodal imaging of a WDR19-Stargardt patient, harboring p.(Ser485Ile) and a novel c.(3183+1_3184-1)_(3261+1_3262-1)del variant, with 43 ABCA4-Stargardt patients. Age at onset, visual acuity, Ishihara color vision, color fundus, fundus autofluorescence (FAF), spectral-domain optical coherence tomography (OCT) images, microperimetry and electroretinography (ERG) were evaluated. First symptom of WDR19 patient was nyctalopia at the age of 5 years. After the age of 18 years, OCT showed hyper-reflectivity at the level of the external limiting membrane/outer nuclear layer. There was abnormal cone and rod photoreceptor function on ERG. Widespread fundus flecks appeared, followed by perifoveal photoreceptor atrophy. Fovea and peripapillary retina remained preserved until the latest exam at 25 years of age. ABCA4 patients had median age of onset at 16 (range 5-60) years and mostly displayed typical Stargardt triad. A total of 19% had foveal sparing. In comparison to ABCA4 patients, the WDR19 patient had a relatively large foveal preservation and severe rod photoreceptor impairment; however, it was still within the ABCA4 disease spectrum. Addition of WDR19 in the group of genes producing phenocopies of Stargardt disease underlines the importance of genetic testing and may help to understand its pathogenesis.

PRPH2-Associated Retinopathy: Novel Variants and Genotype-Phenotype Correlations

PURPOSE

A broad spectrum of autosomal-dominant inherited retinal diseases (IRDs), ranging from mild macular pattern dystrophy to severe cone-rod degeneration, is associated with PRPH2 variants (peripherinopathies). We present detailed clinical and molecular characterization of patients affected by peripherinopathies, aiming to expand the mutational spectrum, and propose novel genotype-phenotype correlations.

DESIGN

Observational, retrospective case series.

PARTICIPANTS

Patients with an IRD related to a molecularly proven PRPH2 variant.

METHODS

Data from ophthalmic examinations and retinal imaging were collected for each follow-up visit. The standard imaging protocol included OCT, blue-light autofluorescence, near-infrared autofluorescence, and ultra-widefield fundus imaging. Genetic analysis was performed with a genomic approach by next-generation sequencing.

MAIN OUTCOME MEASURES

Results of ophthalmic examination, retinal imaging, and molecular genetic analysis.

RESULTS

Overall, a total of 19 patients with an IRD and a (likely) pathogenic PRPH2 variant were identified. Their age at presentation had a median of 48 years, whereas the symptomatic disease onset was in their 30s or 40s in 74% of cases. The median follow-up time was 4 years. Clinically, 6 patients were diagnosed with cone-rod dystrophy and 13 with pattern dystrophy. Among the 13 PRPH2 pathogenic variants identified in our cohort, 7 were missense, 3 nonsense, 2 frame shifting, and 1 splice site. Missense variants in the D2 loop were associated with cone-rod dystrophies and poor visual prognosis, whereas predicted loss-of-function alleles with pattern dystrophies and retention of a good visual function into adulthood. Overall, the following 7 variants were novel and never associated to a clinical phenotype: c.68delT, c.290G>A, c.413T>G, c.642C>G, c.702_706dupCAGTT, c.771_772delinsGA, and c.850C>G.

CONCLUSIONS

Here, we report the findings of a retrospective case series that provided a detailed clinical and molecular characterization of 19 patients harboring 13 different PRPH2 pathogenic variants, 7 of which were previously unreported, expanding the mutational spectrum of the PRPH2 gene. Loss-of-function variants might be preferentially associated with mild-pattern dystrophies, whereas missense dominant-negative variants might be preferentially associated with severely blinding cone-rod degenerations. Further studies are needed to better define the pathogenetic mechanisms and the functional effects of most variants to allow the development of successful gene therapy.

FINANCIAL DISCLOSURE(S)

Proprietary or commercial disclosure may be found after the references.

Whole exome sequencing analysis identifies novel Stargardt disease-related gene mutations in Chinese Stargardt disease and retinitis pigmentosa patients

OBJECTIVES

To delineate the disease-causing mutations of the Stargardt disease-related genes in Chinese patients diagnosed with Stargardt disease or retinitis pigmentosa (RP) by whole exome sequencing analysis.

METHODS

A total of 123 sporadic RP or Stargardt disease patients and 2 Stargardt disease families were recruited. All sporadic patients and the probands of the families were subjected to whole exome sequencing analysis. The candidate mutations were verified by direct sequencing based on the cosegregation pattern and in 200 control subjects and by the bioinformatics analyses.

RESULTS

A total of three reported ABCA4 mutations were identified in the probands of the two Stargardt disease families. The probands and the affected family members with either homozygous or compound heterozygous mutations showed typical Stargardt disease features, which was absent in their unaffected family members. The cosegregation pattern confirmed the mode of recessive inheritance. Moreover, two sporadic Stargardt disease patients were identified to carry two novel ABCA4 and one PROM1 mutations. In addition, 13 novel variants were found in 119 sporadic RP patients in 7 Stargardt disease-related genes, and 8 novel missense variants were conserved across different species and predicted to be damaging to the protein. All 15 novel variants were absent in our 200 control subjects.

CONCLUSIONS

This study revealed 22.4% study subjects carrying Stargardt disease-related gene mutations with total 15 novel variants in seven Stargardt disease-related genes, assuring that targeted next-generation sequencing analysis is a high throughput strategy to facilitate the clinical diagnosis from suspicious patients and recommended as a routine examination for inherited retinal dystrophies.

Dynamic lipid turnover in photoreceptors and retinal pigment epithelium throughout life

The retinal pigment epithelium-photoreceptor interphase is renewed each day in a stunning display of cellular interdependence. While photoreceptors use photosensitive pigments to convert light into electrical signals, the RPE supports photoreceptors in their function by phagocytizing shed photoreceptor tips, regulating the blood retina barrier, and modulating inflammatory responses, as well as regenerating the 11-cis-retinal chromophore via the classical visual cycle. These processes involve multiple protein complexes, tightly regulated ligand-receptors interactions, and a plethora of lipids and protein-lipids interactions. The role of lipids in maintaining a healthy interplay between the RPE and photoreceptors has not been fully delineated. In recent years, novel technologies have resulted in major advancements in understanding several facets of this interplay, including the involvement of lipids in phagocytosis and phagolysosome function, nutrient recycling, and the metabolic dependence between the two cell types. In this review, we aim to integrate the complex role of lipids in photoreceptor and RPE function, emphasizing the dynamic exchange between the cells as well as discuss how these processes are affected in aging and retinal diseases.

Genetic and Phenotypic Landscape of PRPH2-Associated Retinal Dystrophy in Japan

Peripherin-2 (PRPH2) is one of the causative genes of inherited retinal dystrophy. While the gene is relatively common in Caucasians, reports from Asian ethnicities are limited. In the present study, we report 40 Japanese patients from 30 families with PRPH2-associated retinal dystrophy. We identified 17 distinct pathogenic or likely pathogenic variants using next-generation sequencing. Variants p.R142W and p.V200E were relatively common in the cohort. The age of onset was generally in the 40’s; however, some patients had earlier onset (age: 5 years). Visual acuity of the patients ranged from hand motion to 1.5 (Snellen equivalent 20/13). The patients showed variable phenotypes such as retinitis pigmentosa, cone-rod dystrophy, and macular dystrophy. Additionally, intrafamilial phenotypic variability was observed. Choroidal neovascularization was observed in three eyes of two patients with retinitis pigmentosa. The results demonstrate the genotypic and phenotypic variations of the disease in the Asian cohort.

Multifocal Pattern Dystrophy Simulating Fundus Flavimaculatus: Multimodal Imaging for Early Diagnosis

Multifocal pattern dystrophy simulating fundus flavimaculatus (MPDSFF) is a clinical entity characterized by several clinicopathological, angiographic, tomographic, and electrophysiological findings. A 58-year-old caucasian female patient presented with bilateral floaters and metamorphopsia. Best-corrected visual acuity (VA) was 6/6 in both eyes and intraocular pressure was 14 and 15 mm Hg, respectively. Fundus examination, optical coherence tomography (OCT), autofluoresence (AF), fluorescein angiography (FA) and pattern Electroretinogram were employed for the diagnosis of this case. Clinical and imaging findings were consistent with MPDSFF. Noticeable progression was observed in OCT scans 6 months following the baseline visit, while no significant changes were observed over the following 12 months. Prognosis of VA in MPDSFF patients may remain relatively good even in the presence of considerable anatomic changes. Disease progression may be slow and significant reduction in VA may present only secondary to a choroidal neovascular membrane. Patient follow-up should include OCT scans, PERG, and AF in addition to VA and dilated fundus examination every 6–12 months. As relevant literature is limited and no effective treatment modality has been employed for this clinical entity, the identification of the cellular death pathway in pattern dystrophies may lead to an applicable management approach.

Optical coherence tomography findings and choroidal neovascular membrane detectability with optical coherence tomography angiography in different subtypes of pattern dystrophy

CLINICAL RELEVANCE

Optical coherence tomography angiography (OCTA) is a useful method for determining choroidal neovascular membranes (CNVM) in different subtypes of pattern dystrophy.

BACKGROUND

We aimed to evaluate the optical coherence tomography (OCT) findings in different subtypes of pattern dystrophy and to detect CNVM not detectable by conventional method using OCTA.

METHODS

Of 55 eyes included in this retrospective, cross-sectional study, adult onset vitelliform macular dystrophy was present in 42 eyes (32 eyes vitelliform stage-10 eyes vitelliruptive stage), butterfly-shaped pattern dystrophy in 8 eyes, and multifocal pattern dystrophy simulating fundus flavimaculatus in 5 eyes. Fluorescein angiography (FA), fundus autofluorescence, OCT and OCTA imaging were performed in all cases.

RESULTS

The study included 55 eyes of 29 patients, of which 21 were female and 8 were male. On OCT, 25 eyes had hyperreflective dots, 14 eyes had a disruption in the ellipsoid zone (EZ), and 6 eyes had atrophy in the outer retinal layers, and these findings were detected in all subtypes. Findings consistent with CNVM were detected in 1 eye using FA, 3 eyes using OCT and 5 eyes in OCTA.

CONCLUSION

In this study, we demonstrated that in different subtypes of pattern dystrophies OCT findings such as hyperreflective dots, disruption in the EZ, atrophy in the outer retinal layers and CNVM can be seen, and that a quiescent CNVM lesion, which cannot be detected by conventional methods, can be detected by OCTA, a new imaging method.

Treatment and longitudinal follow-up of CNV associated with pattern dystrophy with novel PRPH2 variant

BACKGROUND

Peripherin-2 (PRPH2) is a transmembrane glycoprotein crucial for the morphogenesis and stabilization of the photoreceptor outer segments. Variations in PRPH2 gene are associated with vision-threatening diseases.

METHODS

Clinical manifestations and multimodal imaging were presented, as well as treatment history and six-year follow-up. In addition, genetic testing was performed to confirm the diagnosis.

RESULTS

In this report, we present an extremely rare case of choroidal neovascularization (CNV) secondary to pattern dystrophy simulating fundus flavimaculatus (PDSFF). Multimodal imaging showed typical symmetric yellow flecks in posterior pole and choroidal neovascularization requiring timely treatment. A novel nonsense variant of c.552 C > G; p.Y184X in PRPH2 gene was detected. The patient received intravitreal anti-vascular endothelial growth factor (anti-VEGF) treatment and maintained a good vision after six years.

CONCLUSION

We described a novel PRPH2 variant (Y184X) associated with PDSFF, its multimodal imaging, and long-term prognosis. Intravitreal anti-VEGF treatment can offer excellent visual prognosis in patients with PDSFF-associated CNV.

PRPH2 mutation update: In silico assessment of 245 reported and 7 novel variants in patients with retinal disease

Mutations in PRPH2, encoding peripherin-2, are associated with the development of a wide variety of inherited retinal diseases (IRDs). To determine the causality of the many PRPH2 variants that have been discovered over the last decades, we surveyed all published PRPH2 variants up to July 2020, describing 720 index patients that in total carried 245 unique variants. In addition, we identified seven novel PRPH2 variants in eight additional index patients. The pathogenicity of all variants was determined using the ACMG guidelines. With this, 107 variants were classified as pathogenic, 92 as likely pathogenic, one as benign, and two as likely benign. The remaining 50 variants were classified as variants of uncertain significance. Interestingly, of the total 252 PRPH2 variants, more than half (n = 137) were missense variants. All variants were uploaded into the Leiden Open source Variation and ClinVar databases. Our study underscores the need for experimental assays for variants of unknown significance to improve pathogenicity classification, which would allow us to better understand genotype-phenotype correlations, and in the long-term, hopefully also support the development of therapeutic strategies for patients with PRPH2-associated IRD.

An Overview of the Genetics of ABCA4 Retinopathies, an Evolving Story

Stargardt disease (STGD1) and ABCA4 retinopathies (ABCA4R) are caused by pathogenic variants in the ABCA4 gene inherited in an autosomal recessive manner. The gene encodes an importer flippase protein that prevents the build-up of vitamin A derivatives that are toxic to the RPE. Diagnosing ABCA4R is complex due to its phenotypic variability and the presence of other inherited retinal dystrophy phenocopies. ABCA4 is a large gene, comprising 50 exons; to date > 2000 variants have been described. These include missense, nonsense, splicing, structural, and deep intronic variants. Missense variants account for the majority of variants in ABCA4. However, in a significant proportion of patients with an ABCA4R phenotype, a second variant in ABCA4 is not identified. This could be due to the presence of yet unknown variants, or hypomorphic alleles being incorrectly classified as benign, or the possibility that the disease is caused by a variant in another gene. This underlines the importance of accurate genetic testing. The pathogenicity of novel variants can be predicted using in silico programs, but these rely on databases that are not ethnically diverse, thus highlighting the need for studies in differing populations. Functional studies in vitro are useful towards assessing protein function but do not directly measure the flippase activity. Obtaining an accurate molecular diagnosis is becoming increasingly more important as targeted therapeutic options become available; these include pharmacological, gene-based, and cell replacement-based therapies. The aim of this review is to provide an update on the current status of genotyping in ABCA4 and the status of the therapeutic approaches being investigated.

Fundus Autofluorescence and Clinical Applications

Fundus autofluorescence (FAF) has allowed in vivo mapping of retinal metabolic derangements and structural changes not possible with conventional color imaging. Incident light is absorbed by molecules in the fundus, which are excited and in turn emit photons of specific wavelengths that are captured and processed by a sensor to create a metabolic map of the fundus. Studies on the growing number of FAF platforms has shown each may be suited to certain clinical scenarios. Scanning laser ophthalmoscopes, fundus cameras, and modifications of these each have benefits and drawbacks that must be considered before and after imaging to properly interpret the images. Emerging clinical evidence has demonstrated the usefulness of FAF in diagnosis and management of an increasing number of chorioretinal conditions, such as age-related macular degeneration, central serous chorioretinopathy, retinal drug toxicities, and inherited retinal degenerations such as retinitis pigmentosa and Stargardt disease. This article reviews commercial imaging platforms, imaging techniques, and clinical applications of FAF.

Exploring the choroidal vascular labyrinth and its molecular and structural roles in health and disease

The choroid is a key player in maintaining ocular homeostasis and plays a role in a variety of chorioretinal diseases, many of which are poorly understood. Recent advances in the field of single-cell RNA sequencing have yielded valuable insights into the properties of choroidal endothelial cells (CECs). Here, we review the role of the choroid in various physiological and pathophysiological mechanisms, focusing on the role of CECs. We also discuss new insights regarding the phenotypic properties of CECs, CEC subpopulations, and the value of measuring transcriptomics in primary CEC cultures derived from post-mortem eyes. In addition, we discuss key phenotypic, structural, and functional differences that distinguish CECs from other endothelial cells such as retinal vascular endothelial cells. Understanding the specific clinical and molecular properties of the choroid will shed new light on the pathogenesis of the broad clinical range of chorioretinal diseases such as age-related macular degeneration, central serous chorioretinopathy and other diseases within the pachychoroid spectrum, uveitis, and diabetic choroidopathy. Although our knowledge is still relatively limited with respect to the clinical features and molecular pathways that underlie these chorioretinal diseases, we summarise new approaches and discuss future directions for gaining new insights into these sight-threatening diseases and highlight new therapeutic strategies such as pluripotent stem cell‒based technologies and gene therapy.

Clinical and molecular findings in patients with pattern dystrophy

Purposes: To study the clinical and genetic background of a series of Italian patients affected by pattern dystrophy (PD).Methods: We reviewed patients with a clinical diagnosis of PD examined at the Eye Clinic in Florence from 2012 to 2019. We took into consideration patients with a standard ophthalmological examination, personal and familial ophthalmological history, fundus imaging, and molecular genetic analysis of genes PRPH2 and BEST1. We labelled patients with BEST1 and PRPH2 mutations as m-PD group (mutated) whereas patients with no mutations in these 2 genes as nm-PD group (non-mutated).Results: Seventy-seven PD patients were assessed (average age 59.7 ± 14.2, range 31-88 years). Fifty patients were placed in the nm-PD group and 27 in the m-PD. Pathogenic BEST1 and PRPH2 mutations were detected in 7% and 22% of PD patients, respectively. In total, we reported 1 BEST1 and 8 PRPH2 novel mutations. Ten patients were characterized by drusen in the nm-PD group whereas in no patients in the m-PD group drusen were detected at the fundus.Conclusions: An important proportion of patients affected by PD showed BEST1 or PRPH2 mutations. Patients affected by drusen represent a different sub-phenotype. Genetic examination is recommended for a correct clinical management.

Systemic complement activation levels in Stargardt disease

Purpose

Preclinical research provides evidence for the complement system as a potential common pathway in Stargardt disease (STGD1) and age-related macular degeneration (AMD) leading to retinal pigment epithelium (RPE) loss. However, systemic complement activation has not yet been assessed in STGD1 patients. We conducted a cross-sectional case-control study to assess systemic complement activation in STGD1 patients and its association with disease severity.

Methods

Systemic concentrations of complement component C3 and its degradation product C3d were compared between 80 STGD1 patients and 80 controls that were frequency matched for age and sex. The C3d/C3 ratio was used as parameter of systemic complement activation. Within the STGD1 cohort, we additionally examined the association between the C3d/C3 ratio, demographic and behavioural factors (age, sex, smoking and BMI), and measures of disease severity (age at onset, visual acuity, and area of atrophy).

Results

The C3d/C3 ratio did not significantly differ between patients (mean C3d/C3 ratio 3.5±1.4) and controls (mean C3d/C3 ratio 3.6±1.0), mean difference -0.156 (p = 0.804, independent samples t-test). The overall effect size was 8% (95% confidence interval, 3–15%). Elevated C3d/C3 ratios (>8.1) were found in three patients who all had a concomitant inflammatory condition at the time of blood draw. Within the patient cohort, C3 levels were associated with sex (mean difference -134, p = 0.001, independent samples t-test) and BMI (correlation coefficient 0.463, p<0.001, Spearman’s Correlation).

Conclusions

Systemic complement levels were not elevated in STGD1 patients compared to age and sex matched controls and was not associated with STGD1 severity. Considering the continued absent proof of a systemic contribution of the complement system to RPE loss in STGD1 patients, we hypothesize that complement activation in STGD1 is more likely a local process. In light of upcoming complement-targeted therapies, further studies are needed that measure complement levels in the eye of STGD1 patients.

Shared Features in Retinal Disorders With Involvement of Retinal Pigment Epithelium

When using spectral domain optical coherence tomography (SD-OCT) to inform the status of outer retina, we have noted discrete hyperreflective lesions extending through photoreceptor-attributable bands that have a similar presentation in multiple retinal diseases. These lesions present as either corrugated thickenings of interdigitation zone and ellipsoid zone bands or in later stages as rectangular or pyramidal shaped foci that extend radially through photoreceptor cell-attributable bands. In ABCA4-related and peripherin-2/RDS-disease (PRPH2/RDS), monogenic forms of retinopathy caused by mutations in proteins expressed in photoreceptor cells, these punctate lesions colocalize with fundus flecks in en face images. In fundus albipunctatus and retinitis punctata albescens, diseases caused by mutations in genes (retinol dehydrogenase 5, RDH5; and retinaldehyde-binding protein 1, RLBP1) encoding proteins of the visual cycle, these lesions manifest as white dot-like puncta. Similar aberrations in photoreceptor cell-attributable SD-OCT reflectivity layers manifest as reticular pseudodrusen (RPD) in short-wavelength fundus autofluorescence and near-infrared fundus autofluorescence fundus images and are linked to age-related macular degeneration a complex disease. Despite differences in the etiologies of retinal diseases presenting as fundus flecks, dots and RPD, underlying degenerative processes in photoreceptor cells are signified in SD-OCT scans by the loss of structural features that would otherwise define healthy photoreceptor cells at these foci.

Fundus flavimaculatus-like in myotonic dystrophy: a case report

BACKGROUND

Myotonic dystrophy is an inherited disease characterized by progressive muscle weakness and myotonia. It is a multisystemic disorder that affects different parts of the body, including the eye. Dysfunction of ocular muscles, ptosis and cataract are the most common ophthalmologic manifestations, but it can also present with pigmentary changes in the retina. This report presents and discusses an unusual case of a pigmented pattern dystrophy simulating a fundus flavimaculatus in a patient with myotonic dystrophy.

CASE PRESENTATION

We present a case of a woman with a history of myotonic dystrophy and complaints of progressive vision loss who presented bilateral retinal pigmentary changes in posterior pole and midperiphery. The characteristics and distribution of pigmented deposits, as well as ancillary tests, showed a retinal phenotype compatible with a multifocal pattern dystrophy or a fundus flavimaculatus.

CONCLUSIONS

There are a few publications about retinal disorders in patients with myotonic dystrophy. When macular area is affected it tends to adopt a patterned-shape defined as butterfly dystrophy or reticular dystrophy. To our knowledge, this is the first report of a patient with myotonic dystrophy and multifocal pattern dystrophy or fundus flavimaculatus.

Absence of Genotype/Phenotype Correlations Requires Molecular Diagnostic to Ascertain Stargardt and Stargardt-Like Swiss Patients

We genetically characterized 22 Swiss patients who had been diagnosed with Stargardt disease after clinical examination. We identified in 11 patients (50%) pathogenic bi-allelic ABCA4 variants, c.1760+2T>C and c.4496T>C being novel. The dominantly inherited pathogenic ELOVL4 c.810C>G p.(Tyr270*) and PRPH2-c.422A>G p.(Tyr141Cys) variants were identified in eight (36%) and three patients (14%), respectively. All patients harboring the ELOVL4 c.810C>G p.(Tyr270*) variant originated from the same small Swiss area, identifying a founder mutation. In the ABCA4 and ELOVL4 cohorts, the clinical phenotypes of “flecks”, “atrophy”, and “bull’s eye like” were observed by fundus examination. In the small number of patients harboring the pathogenic PRPH2 variant, we could observe both “flecks” and “atrophy” clinical phenotypes. The onset of disease, progression of visual acuity and clinical symptoms, inheritance patterns, fundus autofluorescence, and optical coherence tomography did not allow discrimination between the genetically heterogeneous Stargardt patients. The genetic heterogeneity observed in the relatively small Swiss population should prompt systematic genetic testing of clinically diagnosed Stargardt patients. The resulting molecular diagnostic is required to prevent potentially harmful vitamin A supplementation, to provide genetic counseling with respect to inheritance, and to schedule appropriate follow-up visits in the presence of increased risk of choroidal neovascularization.

Retinal Glial and Choroidal Vascular Pathology in Donors Clinically Diagnosed With Stargardt Disease

Purpose

The present study investigated retinal glia and choroidal vessels in flatmounts and sections from individuals with clinically diagnosed Stargardt disease (STGD).

Methods

Eyes from three donors clinically diagnosed with STGD were obtained through the Foundation Fighting Blindness (FFB). Genetic testing was performed to determine the disease-causing mutations. Eyes were enucleated and fixed in 4% paraformaldehyde and 0.5% glutaraldehyde. After imaging, retinas were dissected and immunostained for glial fibrillary acidic protein, vimentin, and peanut agglutin. Following RPE removal, the choroid was immunostained with Ulex europaeus agglutinin lectin. For each choroid, the area of affected vasculature, percent vascular area, and choriocapillaris luminal diameters were measured. The retina from one donor was hemisected and cryopreserved or embedded in JB-4 for cross-section analysis.

Results

Genetic testing confirmed the STGD diagnosis in donor 1, whereas a mutation in peripherin 2 was identified in donor 3. Genetic testing was not successful on donor 2. Therefore, only donor 1 can definitively be classified as having STGD. All donors had areas of RPE atrophy within the macular region, which correlated with underlying choriocapillaris loss. In addition, Müller cells formed pre- and subretinal membranes. Subretinal gliotic membranes correlated almost identically with RPE and choriocapillaris loss.

Conclusions

Despite bearing different genetic mutations, all donors demonstrated choriocapillaris loss and Müller cell membranes correlating with RPE loss. Müller cell remodeling was most extensive in the donor with the peripherin mutation, whereas choriocapillaris loss was greatest in the confirmed STGD donor. This study emphasizes the importance of genetic testing when diagnosing macular disease.

Stargardt misdiagnosis: How ocular genetics helps

Ocular Genetics at Wills Eye Hospital sees a wide range of rare disorders for accurate diagnosis. To demonstrate how focused consultation and genetic testing results in precise diagnoses, we investigated false diagnosis rates for patients referred with a diagnosis of Stargardt disease. This is a retrospective review of patients over a 3 year period referred to our Ocular Genetics clinic for possible Stargardt disease, or already holding a diagnosis of Stargardt disease. Results of diagnostic and genetic testing were compared to standard definition of Stargardt. Of 40 patients, 14 (35%) had been misdiagnosed. Four had non-Stargardt phenotype of which three had ABCA4 pathogenic variants with phenotypes inconsistent with Stargardt disease. Two of those with pathogenic ABCA4 variants were related. Nine had pathogenic variants in other different genes with overlapping features of Stargardt disease. One had Thioridazine maculopathy. Our study highlights the essential role of the subspecialty field of ocular genetics in obtaining accurate diagnoses for the delivery of correct counseling and interventional trial eligibility assessment.

Evidence of complement dysregulation in outer retina of Stargardt disease donor eyes

Stargardt macular degeneration (STGD) is a central blinding disease caused by loss of or dysfunctional ABCA4 transporter in both photoreceptors and retinal pigment epithelial (RPE) cells. Toxic bisretinoid-lipofuscin buildup in the RPE cells is a pathological hallmark of STGD patients and its mouse model, the Abca4^-/-. These vitamin A-derived fluorophores have been shown to induce oxidative stress, stimulate complement activity, and cause chronic inflammation of the RPE. In vivo modulation of complement regulatory pathway in the STGD mouse model has partially rescued the STGD phenotype suggesting that complement attack on the RPE is an important etiologic factor in disease pathogenesis. While bisretinoid-dependent complement activation was further evidenced in cultured RPE cells, this pathway has never been investigated directly in the context of RPE from STGD donor eyes. In the current study, we evaluate the complement reactivity in postmortem donor eyes of clinically diagnosed STGD patients. All three STGD donor eyes RPE displayed strong immunoreactivity for an antibody specific to 4-Hydroxynonenal, a lipid peroxidation byproduct. Also, unlike the control eyes, all three STGD donor eyes showed significantly increased membrane attack complex deposition on the RPE cells. In STGD eyes, increased MAC accumulation was mirrored by elevated C3 fragments internalized by the RPE and inversely correlated with the levels of complement factor H, a major complement regulatory protein. Here, we report the first direct evidence of RPE complement dysregulation as a causative factor in developing Stargardt phenotype.

Development of a Genotype Assay for Age-Related Macular Degeneration: The EYE-RISK Consortium

PURPOSE

To develop a genotype assay to assess associations with common and rare age-related macular degeneration (AMD) risk variants, to calculate an overall genetic risk score (GRS), and to identify potential misdiagnoses with inherited macular dystrophies that mimic AMD.

DESIGN

Case-control study.

PARTICIPANTS

Individuals (n = 4740) from 5 European cohorts.

METHODS

We designed single-molecule molecular inversion probes for target selection and used next generation sequencing to sequence 87 single nucleotide polymorphisms (SNPs), coding and splice-site regions of 10 AMD-(related) genes (ARMS2, C3, C9, CD46, CFB, CFH, CFI, HTRA1, TIMP3, and SLC16A8), and 3 genes that cause inherited macular dystrophies (ABCA4, CTNNA1, and PRPH2). Genetic risk scores for common AMD risk variants were calculated based on effect size and genotype of 52 AMD-associated variants. Frequency of rare variants was compared between late AMD patients and control individuals with logistic regression analysis.

MAIN OUTCOME MEASURES

Genetic risk score, association of genetic variants with AMD, and genotype-phenotype correlations.

RESULTS

We observed high concordance rates between our platform and other genotyping platforms for the 69 successfully genotyped SNPs (>96%) and for the rare variants (>99%). We observed a higher GRS for patients with late AMD compared with patients with early/intermediate AMD (P < 0.001) and individuals without AMD (P < 0.001). A higher proportion of pathogenic variants in the CFH (odds ratio [OR] = 2.88; P = 0.006), CFI (OR = 4.45; P = 0.005), and C3 (OR = 6.56; P = 0.0003) genes was observed in late AMD patients compared with control individuals. In 9 patients, we identified pathogenic variants in the PRPH2, ABCA4, and CTNNA1 genes, which allowed reclassification of these patients as having inherited macular dystrophy.

CONCLUSIONS

This study reports a genotype assay for common and rare AMD genetic variants, which can identify individuals at intermediate to high genetic risk of late AMD and enables differential diagnosis of AMD-mimicking dystrophies. Our study supports sequencing of CFH, CFI, and C3 genes because they harbor rare high-risk variants. Carriers of these variants could be amendable for new treatments for AMD that currently are under development.

PRPH2-Related Retinal Diseases: Broadening the Clinical Spectrum and Describing a New Mutation

Over 175 pathogenic mutations in the Peripherin-2 (PRPH2) gene are linked to various retinal diseases. We report the phenotype and genotype of eight families (24 patients) with retinal diseases associated with seven distinct PRPH2 gene mutations. We identified a new mutation, c.824_828+3delinsCATTTGGGCTCCTCATTTGG, in a patient with adult-onset vitelliform macular dystrophy (AVMD). One family with the p.Arg46Ter mutation presented with the already described AVMD phenotype, but another family presented with the same mutation and two heterozygous pathogenic mutations (p.Leu2027Phe and p.Gly1977Ser) in the ATP Binding Cassette Subfamily A Member 4 (ABCA4) gene that cause extensive chorioretinal atrophy (ECA), which could be a blended phenotype. The p.Lys154del PRPH2 gene mutation associated with the p.Arg2030Glu mutation in the ABCA4 gene was found in a patient with multifocal pattern dystrophy simulating fundus flavimaculatus (PDsFF), for whom we considered ABCA4 as a possible modifying gene. The mutation p.Gly167Ser was already known to cause pattern dystrophy, but we also found ECA, PDsFF, and autosomal-dominant retinitis pigmentosa (ADRP) as possible phenotypes. Finally, we identified the mutation p.Arg195Leu in a large family with common ancestry, which previously was described to cause central areolar choroidal dystrophy (CACD), but we also found ADRP and observed that it caused ECA more frequently than CACD in this family.

Foveal Sparing in Central Retinal Dystrophies

Purpose

To describe foveal sparing (FS) in central retinal dystrophies (RD).

Methods

Participants for this retrospective study were identified from the retinal dystrophy database of the Department of Ophthalmology at Radboud University Medical Center. FS was defined as an intact foveal structure surrounded by at least 180° of chorioretinal atrophy, and a best-corrected visual acuity (BCVA) of <1.0 logMAR (>20/200 Snellen). Eligible eyes were identified using fundus autofluorescence (FAF) images, and FS was confirmed using near-infrared reflectance (NIR) imaging and spectral-domain optical coherence tomography when available. Clinical and demographic data were extracted from medical records. We performed quantification of FS and chorioretinal atrophic areas using semiautomated software on fundus autofluorescence and NIR images. We calculated the chronologic change using eye-wise linear regression.

Results

We identified 36 patients (56 eyes) with FS. RDs included: Stargardt disease (STGD1;20 patients), central areolar choroidal dystrophy (CACD; 7 patients), mitochondrial retinal dystrophy (MRD; 6 patients), pseudo-Stargardt pattern dystrophy (PSPD; 3 patients). Median age at first presentation was 60 (interquartile range [IQR] 54-63) years. Median BCVA at first presentation ranged from 20/25 Snellen in STGD1, to 20/38 Snellen in MRD. Progression of the chorioretinal atrophic area ranged from 0.26 (0.25-0.28) mm/year in PSPD, to 0.14 (0.11-0.22) in CACD. Change in FS area over time was similar between the different dystrophies.

Conclusions

The presence of FS in different RDs suggests a disease-independent mechanism that prolongs the survival of the fovea. The associated preservation of BCVA is important for the individual prognosis and has implications for the design of therapeutic trials for RDs.

Case Series: Multimodal Imaging Reveals the Spectrum of Pattern Dystrophies of the Retinal Pigment Epithelium

SIGNIFICANCE

Pattern dystrophies of the retinal pigment epithelium, often misdiagnosed as other macular conditions, were once considered a rare retinal disease. However, an increasing number of cases have recently been discovered owing to advancements in multimodal imaging and increased awareness of the condition.

PURPOSE

The purposes of this study were to increase awareness of pattern dystrophies and to review how to accurately diagnose and manage pattern dystrophies by understanding their presentation on fundus autofluorescence, optical coherence tomography, and electrodiagnostic testing.

CASE SERIES

Three cases of patients diagnosed as having pattern dystrophies are reported. In case 1, fundus autofluorescence, optical coherence tomography, and electrodiagnostic testing aid in diagnosing multifocal pattern dystrophy. The same tools are used to diagnose adult-onset foveomacular vitelliform dystrophy in case 2 and reticular pattern dystrophy in case 3.

CONCLUSIONS

Fundus autofluorescence, optical coherence tomography, and electrodiagnostic testing facilitate the proper diagnosis of patients with pattern dystrophies. With increased awareness of pattern dystrophies and increased use of multimodal imaging, pattern dystrophies will likely no longer be considered rare.

Wide-field fundus autofluorescence imaging in patients with hereditary retinal degeneration: a literature review

Background

Inherited retinal degeneration (IRD) refers to a heterogenous group of progressive diseases that cause death of photoreceptor cells and subsequent vision loss. These diseases often affect the peripheral retina, objective evaluation of which has been difficult until recently. Fundus autofluorescence (FAF) is a non-invasive retinal imaging technique that depicts the distribution of intrinsic fluorophores in the retina. The primary source of retinal autofluorescence is lipofuscin, which is contained in the retinal pigment epithelium (RPE). Excessive accumulation of lipofuscin and a window defect attributable to loss of photoreceptor pigment result in increased FAF whereas loss of the RPE results in decreased FAF. These changes can be seen during the course of IRD.

Mainbody

While conventional modalities are limited in their angle of view, recent technologic advances, known as wide-field and ultra-widefield FAF imaging, have enabled visualization of the far peripheral retina. Although clinical application of this technique in patients with IRD is still in its infancy, some studies have already indicated its usefulness. For example, an area with decreased FAF correlates well with a visual field defect in an eye with retinitis pigmentosa (RP) or cone-rod dystrophy. An abnormal FAF pattern may help in the diagnosis of IRD and associated diseases. In addition, female carriers of X-linked RP and female choroideremia show characteristic appearance. Conversely, absence of abnormal FAF despite severe retinal degeneration helps differentiation of cancer-associated retinopathy.

Conclusion

This paper reviews the principles of FAF, wide-field imaging, and findings in specific diseases. Wide-field imaging, particularly wide-field FAF, will provide further information for the characteristics, prognosis, and pathogenesis of IRD.

Lessons learned from quantitative fundus autofluorescence

Quantitative fundus autofluorescence (qAF) is an approach that is built on a confocal scanning laser platform and used to measure the intensity of the inherent autofluorescence of retina elicited by short-wavelength (488 nm) excitation. Being non-invasive, qAF does not interrupt tissue architecture, thus allowing for structural correlations. The spectral features, cellular origin and topographic distribution of the natural autofluorescence of the fundus indicate that it is emitted from retinaldehyde-adducts that form in photoreceptor cells and accumulate, under most conditions, in retinal pigment epithelial cells. The distributions and intensities of fundus autofluorescence deviate from normal in many retinal disorders and it is widely recognized that these changing patterns can aid in the diagnosis and monitoring of retinal disease. The standardized protocol employed by qAF involves the normalization of fundus grey levels to a fluorescent reference installed in the imaging instrument. Together with corrections for magnification and anterior media absorption, this approach facilitates comparisons with serial images and images acquired within groups of patients. Here we provide a comprehensive summary of the principles and practice of qAF and we highlight recent efforts to elucidate retinal disease processes by combining qAF with multi-modal imaging.

Macular Dystrophy and Cone-Rod Dystrophy Caused by Mutations in the RP1 Gene: Extending the RP1 Disease Spectrum

Purpose

To describe the clinical and genetic spectrum of RP1-associated retinal dystrophies.

Methods

In this multicenter case series, we included 22 patients with RP1-associated retinal dystrophies from 19 families from The Netherlands and Japan. Data on clinical characteristics, visual acuity, visual field, ERG, and retinal imaging were extracted from medical records over a mean follow-up of 8.1 years.

Results

Eleven patients were diagnosed with autosomal recessive macular dystrophy (arMD) or autosomal recessive cone-rod dystrophy (arCRD), five with autosomal recessive retinitis pigmentosa (arRP), and six with autosomal dominant RP (adRP). The mean age of onset was 40.3 years (range 14-56) in the patients with arMD/arCRD, 26.2 years (range 18-40) in adRP, and 8.8 years (range 5-12) in arRP patients. All patients with arMD/arCRD carried either the hypomorphic p.Arg1933* variant positioned close to the C-terminus (8 of 11 patients) or a missense variant in exon 2 (3 of 11 patients), compound heterozygous with a likely deleterious frameshift or nonsense mutation, or the p.Gln1916* variant. In contrast, all mutations identified in adRP and arRP patients were frameshift and/or nonsense variants located far from the C-terminus.

Conclusions

Mutations in the RP1 gene are associated with a broad spectrum of progressive retinal dystrophies. In addition to adRP and arRP, our study provides further evidence that arCRD and arMD are RP1-associated phenotypes as well. The macular involvement in patients with the hypomorphic RP1 variant suggests that macular function may remain compromised if expression levels of RP1 do not reach adequate levels after gene augmentation therapy.

Efficacy of anti-VEGF in the treatment of choroidal neovascular membrane secondary to pattern dystrophy simulating fundus flavimaculatus

Pattern dystrophies are a group of inherited disorders of the retinal pigment epithelium. A 44-year-old female came with loss of vision in her right eye. The fundus of both eyes showed flecks in the posterior pole with a CNVM in the right eye. FFA and SD OCT confirmed the presence of CNVM. The patient underwent treatment with anti-VEGF injection. Post treatment, the vision improved with a reduction in subretinal fluid along with a scarring CNVM. To conclude, we report an extremely rare case of PDSFF associated CNVM and its favourable response to anti-VEGF injection.

Late-onset pattern macular dystrophy mimicking ABCA4 and PRPH2 disease is caused by a homozygous frameshift mutation in ROM1

ROM1 (retinal outer segment membrane protein 1) is a 351-amino acid integral membrane protein on Chromosome 11q, with high structural similarity to PRPH2/RDS. Localized at the rims of photoreceptor outer segments (OSs), it is required for the maintenance of OS structure. Here, we describe a case with a phenotypic manifestation of a homozygous single-base pair deletion, c.712delC (p.Leu238Cysfs*78) in the ROM1 gene, resulting in early termination at exon 2. The variant was detected by whole-exome sequencing (WES) in a 63-yr-old Caucasian woman with late-onset pattern macular dystrophy. Notably, although the phenotype resembles those caused by pathogenic variants in ABCA4 or RDS/PRPH2, no pathogenic variants in these, or any other plausible candidate genes, were identified by WES. Clinical features include the presence of hyperautofluorescent flecks, relative sparing of the central macula, and preserved visual acuity. Reduced visual sensitivity was detected among flecked regions in the retina; however, full-field electroretinogram testing revealed no generalized cone dysfunction. The described first case of the complete loss of ROM1 protein function in the retina suggests its sufficiency for late-onset macular dystrophy. ROM1 and PRPH2 pattern macular dystrophies exhibit phenotype overlap, which may be attributable to their shared role in maintenance of the photoreceptor outer segment structure.

Identification of novel pathogenic ABCA4 variants in a Han Chinese family with Stargardt disease

Stargardt disease (STGD1, OMIM 248200) is a common hereditary juvenile or early adult onset macular degeneration. It ultimately leads to progressive central vision loss. Here, we sought to identify gene mutations associated with STGD1 in a three-generation Han Chinese pedigree by whole exome sequencing and Sanger sequencing. Two novel potentially pathogenic variants in a compound heterozygous state, c.3607G>T (p.(Gly1203Trp)) and c.6722T>C (p.(Leu2241Pro)), in the ATP binding cassette subfamily A member 4 gene (ABCA4) were identified as contributing to the family’s STGD1 phenotype. These variants may impact the ABCA4 protein structure and reduce the retinal-activated ATPase activity, leading to abnormal all-trans retinal accumulation in photoreceptor outer segments and in retinal pigment epithelium cells. The present study broadens the mutational spectrum of the ABCA4 responsible for STGD1. A combination of whole exome sequencing and Sanger sequencing is likely to be a time-saving and cost-efficient approach to screen pathogenic variants in genetic disorders caused by sizable genes, as well as avoiding misdiagnosis. These results perhaps refine genetic counseling and ABCA4-targetted treatments for families affected by STGD1.