Highly Variable Disease Courses in Siblings with Stargardt Disease.

PURPOSE: To investigate intersibling phenotypic concordance in Stargardt disease (STGD1). DESIGN: Retrospective cohort study. PARTICIPANTS: Siblings with genetically confirmed STGD1 and at least 1 available fundus autofluorescence (FAF) image of both eyes. METHODS: We compared age at onset within families. Disease duration was matched to investigate differences in best-corrected visual acuity (BCVA) and compared the survival time for reaching severe visual impairment (<20/200 Snellen or >1.0 logarithm of the minimum angle of resolution [logMAR]). Central retinal atrophy area was quantified independently by 2 experienced graders using semiautomated software and compared between siblings. Both graders performed qualitative assessment of FAF and spectral-domain (SD) OCT images to identify phenotypic differences. MAIN OUTCOME MEASURES: Differences in age at onset, disease duration-matched BCVA, time to severe visual impairment development, FAF atrophy area, FAF patterns, and genotypes. RESULTS: Substantial differences in age at onset were present in 5 of 17 families, ranging from 13 to 39 years. Median BCVA at baseline was 0.60 logMAR (range, -0.20 to 2.30 logMAR; Snellen equivalent, 20/80 [range, 20/12-hand movements]) in the right eye and 0.50 logMAR (range, -0.20 to 2.30 logMAR; Snellen equivalent, 20/63 [range, 20/12-hand movements]) in the left eye. Disease duration-matched BCVA was investigated in 12 of 17 families, and the median difference was 0.41 logMAR (range, 0.00-1.10 logMAR) for the right eye and 0.41 logMAR (range, 0.00-1.08 logMAR) for the left eye. We observed notable differences in time to severe visual impairment development in 7 families, ranging from 1 to 29 years. Median central retinal atrophy area was 11.38 mm2 in the right eye (range, 1.98-44.78 mm2) and 10.59 mm2 in the left eye (range, 1.61-40.59 mm2) and highly comparable between siblings. Similarly, qualitative FAF and SD OCT phenotypes were highly comparable between siblings. CONCLUSIONS: Phenotypic discordance between siblings with STGD1 carrying the same ABCA4 variants is a prevalent phenomenon. Although the FAF phenotypes are highly comparable between siblings, functional outcomes differ substantially. This complicates both sibling-based prognosis and genotype-phenotype correlations and has important implications for patient care and management.

The absence of fundus abnormalities in Stargardt disease.

PURPOSE: To raise awareness of Stargardt disease (STGD1) patients without fundus abnormalities. METHODS: Medical records were evaluated for age at onset, initial symptoms and diagnosis, reason for delay of diagnosis, age at STGD1 diagnosis, best-corrected visual acuity (BCVA), ophthalmoscopy, fundus photography, fundus autofluorescence (FAF), fluorescein angiography (FA), spectral-domain optical coherence tomography (SD-OCT), full-field electroretinography (ffERG), color vision test, and the presence of ABCA4 variants. RESULTS: In 11.1% of our STGD1 cohort of 280 patients, no fundus abnormalities were observed at first ophthalmic consultation. The median age at onset was 8 years (range, 1-18). There was a median delay in diagnosis of 3 years (range, 0-19) in 27 out of 31 patients, which resulted in a median age at diagnosis of 12 years (range, 7-26). Patients were misdiagnosed with amblyopia, myopia, optic disk pathology, mental health problems, tension headache, neuritis bulbaris, and uveitis. Subtle abnormalities, such as lipofuscin accumulation, were seen on FAF at an earlier disease stage than in ophthalmoscopy. On SD-OCT, this included a thickened external limiting membrane. Color vision tests showed red-green insufficiency in 79% of patients. Reduced ERG amplitudes were only present in 26% (N = 8) and a dark choroid sign in 65% of the patients. Visual acuity considerably fluctuated in the first 5 years after onset. The majority of the patients (65%) carried a least one variant with a severe effect on ABCA4 function. CONCLUSIONS: Childhood-onset STGD1 patients were diagnosed with a delay of median 3 years. The presence of accurate competence, equipment, and the possibility for genetic screening is required; therefore, we recommend to refer children with visual complaints without initial fundus abnormalities to a specialized ophthalmologic center. In particular, to diagnose patients at an early stage of disease is of increased importance with the advent of new therapeutic possibilities.

Disruption of the basal body protein POC1B results in autosomal-recessive cone-rod dystrophy.

Exome sequencing revealed a homozygous missense mutation (c.317C>G [p.Arg106Pro]) in POC1B, encoding POC1 centriolar protein B, in three siblings with autosomal-recessive cone dystrophy or cone-rod dystrophy and compound-heterozygous POC1B mutations (c.199_201del [p.Gln67del] and c.810+1G>T) in an unrelated person with cone-rod dystrophy. Upon overexpression of POC1B in human TERT-immortalized retinal pigment epithelium 1 cells, the encoded wild-type protein localized to the basal body of the primary cilium, whereas this localization was lost for p.Arg106Pro and p.Gln67del variant forms of POC1B. Morpholino-oligonucleotide-induced knockdown of poc1b translation in zebrafish resulted in a dose-dependent small-eye phenotype, impaired optokinetic responses, and decreased length of photoreceptor outer segments. These ocular phenotypes could partially be rescued by wild-type human POC1B mRNA, but not by c.199_201del and c.317C>G mutant human POC1B mRNAs. Yeast two-hybrid screening of a human retinal cDNA library revealed FAM161A as a binary interaction partner of POC1B. This was confirmed in coimmunoprecipitation and colocalization assays, which both showed loss of FAM161A interaction with p.Arg106Pro and p.Gln67del variant forms of POC1B. FAM161A was previously implicated in autosomal-recessive retinitis pigmentosa and shown to be located at the base of the photoreceptor connecting cilium, where it interacts with several other ciliopathy-associated proteins. Altogether, this study demonstrates that POC1B mutations result in a defect of the photoreceptor sensory cilium and thus affect cone and rod photoreceptors.

Early-onset stargardt disease: phenotypic and genotypic characteristics.

OBJECTIVE: To describe the phenotype and genotype of patients with early-onset Stargardt disease. DESIGN: Retrospective cohort study. PARTICIPANTS: Fifty-one Stargardt patients with age at onset ≤10 years. METHODS: We reviewed patient medical records for age at onset, medical history, initial symptoms, best-corrected visual acuity (BCVA), ophthalmoscopy, fundus photography, fundus autofluorescence (FAF), fluorescein angiography (FA), spectral-domain optical coherence tomography (SD-OCT), and full-field electroretinography (ffERG). The ABCA4 gene was screened for mutations. MAIN OUTCOME MEASURES: Age at onset, BCVA, fundus appearance, FAF, FA, SD-OCT, ffERG, and presence of ABCA4 mutations. RESULTS: The mean age at onset was 7.2 years (range, 1-10). The median times to develop BCVA of 20/32, 20/80, 20/200, and 20/500 were 3, 5, 12, and 23 years, respectively. Initial ophthalmoscopy in 41 patients revealed either no abnormalities or foveal retinal pigment epithelium (RPE) changes in 10 and 9 patients, respectively; the other 22 patients had foveal atrophy, atrophic RPE lesions, and/or irregular yellow-white fundus flecks. On FA, there was a "dark choroid" in 21 out of 29 patients. In 14 out of 50 patients, foveal atrophy occurred before flecks developed. On FAF, there was centrifugal expansion of disseminated atrophic spots, which progressed to the eventual profound chorioretinal atrophy. Spectral-domain OCT revealed early photoreceptor damage followed by atrophy of the outer retina, RPE, and choroid. On ffERG in 26 patients, 15 had normal amplitudes, and 11 had reduced photopic and/or scotopic amplitudes at their first visit. We found no correlation between ffERG abnormalities and the rate of vision loss. Thirteen out of 25 patients had progressive ffERG abnormalities. Finally, genetic screening of 44 patients revealed ≥2 ABCA4 mutations in 37 patients and single heterozygous mutations in 7. CONCLUSIONS: In early-onset Stargardt, initial ophthalmoscopy can reveal no abnormalities or minor retinal abnormalities. Yellow-white flecks can be preceded by foveal atrophy and may be visible only on FAF. Although ffERG is insufficient for predicting the rate of vision loss, abnormalities can develop. Over time, visual acuity declines rapidly in parallel with progressive retinal degeneration, resulting in profound chorioretinal atrophy. Thus, early-onset Stargardt lies at the severe end of the spectrum of ABCA4-associated retinal phenotypes.

Charles Bonnet syndrome in patients with Stargardt disease: prevalence and risk factors.

AIMS: To describe the prevalence of the Charles Bonnet syndrome (CBS) and search for potential CBS risk factors in a Dutch Stargardt disease (STGD1) cohort. METHODS: Eighty-three patients with STGD1 were screened for CBS. They underwent a full eye examination. All patients completed the social functioning domain of the 36-Item Short Form Health Survey questionnaire. Participants suspected of CBS were interviewed to further evaluate their visual hallucinations. RESULTS: CBS prevalence was 8.4%. Six out of seven patients with CBS were women. CBS was not associated with age (p=0.279, Mann-Whitney). Patients with CBS had a significant lower social functioning score (p<0.05, Mann-Whitney). All seven patients with CBS were in the category of vision impairment (visual acuity <6/12, but ≥3/60). Moreover, first hallucinations manifested after a drop in visual acuity. The retinal atrophic area of the worst eye tended to be lower in the CBS group (range 0.11-9.86 mm2) as compared with controls (range 0-180 mm2). There was no relation between the position of the scotoma and the location of the visual hallucinations. CONCLUSION: The relative high CBS prevalence in STGD1 suggests that CBS may be more prevalent in younger ophthalmic patients than currently presumed. In this specific group of patients, we established social isolation and acquired vision impairment as risk factors for CBS. There was a female preponderance among patients with CBS. Age and retinal pigment epithelium atrophy were not identified as significant risk factors. We should actively diagnose CBS in patients of any age who fulfil the criteria for the category vision impairment, especially in cases where social isolation is suspected.

Correlation of Morphology and Function of Flecks Using Short-Wave Fundus Autofluorescence and Microperimetry in Patients With Stargardt Disease.

Purpose: The purpose of this study was to evaluate the functional relevance of longitudinal changes in hyperautofluorescent areas and flecks in Stargardt disease (STGD1) using short-wavelength autofluorescence (SW-AF) imaging. Methods: In this prospective, longitudinal study, 31 patients with STGD1 (56 eyes) underwent microperimetry (MP) and SW-AF imaging twice in 3 to 5 years. A total of 760 MP test points were included in the statistical analysis based on stable fixation and accurate alignment of SW-AF and MP. Autofluorescence intensity was qualitatively assessed in all MP test points. Small circumscriptive hyperautofluorescent lesions were defined as flecks. Longitudinal imaging characteristics observed on SW-AF were classified into the following categories: appearing, disappearing, and stable flecks, stable hyperautofluorescent, and stable background autofluorescence. The relationship between SW-AF intensity changes and MP changes was analyzed using a linear mixed model corrected for baseline sensitivity. Results: Retinal sensitivity declined most in locations without change in SW-AF intensity. Functional decline per year was significantly larger in flecks that disappeared (-0.72 ± 1.30 dB) compared to flecks that appeared (-0.34 ± 0.65 dB), if baseline sensitivity was high (≥10 dB; P < 0.01). The correlation between the change observed on SW-AF and the sensitivity change significantly depended on the sensitivity at baseline (P = 0.000). Conclusions: Qualitative longitudinal assessment of SW-AF poorly reflected the retinal sensitivity loss observed over the course of 3 to 5 years. Translational Relevance: When aiming to assess treatment effect on lesion level, a multimodal end point including MP focused on hyperautofluorescent lesions appears essential but needs further studies on optimizing MP grids, eye-tracking systems, and alignment software.

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.

Lipofuscin-associated photo-oxidative stress during fundus autofluorescence imaging.

PURPOSE: Current standards and guidelines aimed at preventing retinal phototoxicity during intentional exposures do not specifically evaluate the contribution of endogenous photosensitizers. However, certain retinal diseases are characterized by abnormal accumulations of potential photosensitizers such as lipofuscin bisretinoids in the retinal pigment epithelium (RPE). We sought to determine these contributions by a numerical assessment of in-vivo photo-oxidative stress during irradiation of RPE lipofuscin. METHODS: Based on the literature, we calculated the retinal exposure levels, optical filtering of incident radiation by the ocular lens, media, photoreceptors, and RPE melanin, light absorption by lipofuscin, and photochemical effects in the RPE in two situations: exposure to short-wavelength (λ = 488 nm) fundus autofluorescence (SW-AF) excitation light and exposure to indirect (diffuse) sunlight. RESULTS: In healthy persons at age 20, 40, and 60, respectively, the rate of oxygen photoconsumption by lipofuscin increases by 1.3, 1.7, and 2.4 fold during SW-AF-imaging as compared to diffuse sunlight. In patients with STGD1 below the age of 30, this rate was 3.3-fold higher compared to age-matched controls during either sunlight or SW-AF imaging. CONCLUSIONS: Our results suggest that the RPE of patients with STGD1 is generally at increased risk of photo-oxidative stress, while exposure during SW-AF-imaging amplifies this risk. These theoretical results have not yet been verified with in-vivo data due to a lack of sufficiently sensitive in-vivo measurement techniques.

Highly sensitive measurements of disease progression in rare disorders: Developing and validating a multimodal model of retinal degeneration in Stargardt disease.

BACKGROUND: Each inherited retinal disorder is rare, but together, they affect millions of people worldwide. No treatment is currently available for these blinding diseases, but promising new options-including gene therapy-are emerging. Arguably, the most prevalent retinal dystrophy is Stargardt disease. In each case, the specific combination of ABCA4 variants (> 900 identified to date) and modifying factors is virtually unique. It accounts for the vast phenotypic heterogeneity including variable rates of functional and structural progression, thereby potentially limiting the ability of phase I/II clinical trials to assess efficacy of novel therapies with few patients. To accommodate this problem, we developed and validated a sensitive and reliable composite clinical trial endpoint for disease progression based on structural measurements of retinal degeneration. METHODS AND FINDINGS: We used longitudinal data from early-onset Stargardt patients from the Netherlands (development cohort, n = 14) and the United Kingdom (external validation cohort, n = 18). The composite endpoint was derived from best-corrected visual acuity, fundus autofluorescence, and spectral-domain optical coherence tomography. Weighting optimization techniques excluded visual acuity from the composite endpoint. After optimization, the endpoint outperformed each univariable outcome, and showed an average progression of 0.41° retinal eccentricity per year (95% confidence interval, 0.30-0.52). Comparing with actual longitudinal values, the model accurately predicted progression (R2, 0.904). These properties were largely preserved in the validation cohort (0.43°/year [0.33-0.53]; prediction: R2, 0.872). We subsequently ran a two-year trial simulation with the composite endpoint, which detected a 25% decrease in disease progression with 80% statistical power using only 14 patients. CONCLUSIONS: These results suggest that a multimodal endpoint, reflecting structural macular changes, provides a sensitive measurement of disease progression in Stargardt disease. It can be very useful in the evaluation of novel therapeutic modalities in rare disorders.

Differential Disease Progression in Atrophic Age-Related Macular Degeneration and Late-Onset Stargardt Disease.

Purpose: To compare the disease course of retinal pigment epithelium (RPE) atrophy secondary to age-related macula degeneratio (AMD) and late-onset Stargardt disease (STGD1). Methods: Patients were examined longitudinally by fundus autofluorescence, near-infrared reflectance imaging, and best-corrected visual acuity (BCVA). Areas of RPE atrophy were quantified using semi-automated software, and the status of the fovea was evaluated based on autofluorescence and near-infrared reflectance images. Mixed-effects models were used to compare atrophy progression rates. BCVA loss and loss of foveal integrity were analyzed using Turnbull's estimator. Results: A total of 151 patients (226 eyes) with RPE atrophy secondary to AMD and 38 patients (66 eyes) with RPE atrophy secondary to late-onset STGD1 were examined for a median time of 2.3 years (interquartile range, 2.7). Mean baseline age was 74.2 years (SD, 7.6) in AMD and 63.4 (SD, 9.9) in late-onset STGD1 (P = 1.1 × 10-7). Square root atrophy progression was significantly faster in AMD when compared with late-onset STGD1 (0.28 mm/year [SE, 0.01] vs. 0.23 [SE, 0.03]; P = 0.030). In late-onset STGD1, the median survival of the fovea was significantly longer when compared with eyes with AMD (8.60 vs. 3.35 years; P = 0.005) with a trend to a later BCVA loss of ≥3 lines (5.97 vs. 4.37 years; P = 0.382). Conclusions: These natural history data indicate differential disease progression in AMD versus late-onset STGD1. The results underline the relevance of refined phenotyping in elderly patients presenting with RPE atrophy in regard to prognosis and design of interventional trials.

Asymmetric Inter-Eye Progression in Stargardt Disease.

Purpose: Asymmetry in disease progression between left and right eyes can occur in Stargardt disease (STGD1), and this needs to be considered in novel therapeutic trials with a fellow-eye paired controlled design. This study investigated the inter-eye discordance of best-corrected visual acuity (BCVA) and progression of RPE atrophy in STGD1. Methods: We performed a retrospective cohort study collecting 68 STGD1 patients (136 eyes) with ≥1 ABCA4 variants and ≥0.5-year follow-up on BCVA and fundus autofluorescence. We compared inter-eye correlations of RPE atrophy progression between early-onset (≤10 years), intermediate-onset (11-44), and late-onset (≥45) STGD1 and ABCA4 variant combinations by χ2 tests. We identified associations of discordant baseline BCVA and RPE atrophy with discordant RPE atrophy progression by odds ratios (OR). We defined discordance by differences >1.5 interquartile ranges ± first/third interquartiles. Results: Progression of RPE atrophy correlated moderately between eyes (ρ = 0.766), which decreased with later onset (P = 9.8 × 10-7) and lower pathogenicity of ABCA4 combinations (P = 0.007). Twelve patients (17.6%) had discordant inter-eye RPE atrophy progression, associated with baseline discordance of RPE atrophy (OR, 6.50 [1.35-31.34]), but not BCVA (OR, 0.33 [0.04-2.85]). Conclusions: Lower inter-eye correlations are more likely found in late-onset STGD1 and patients carrying low pathogenic ABCA4 combinations. To achieve the highest power in a therapeutic trial, early-phase studies should minimize inter-eye discordance by selecting early-onset STGD1 patients carrying severe ABCA4 variants without evidence of asymmetry at baseline.

Progression of Late-Onset Stargardt Disease.

PURPOSE: Identification of sensitive biomarkers is essential to determine potential effects of emerging therapeutic trials for Stargardt disease. This study aimed to describe the natural history of late-onset Stargardt, and demonstrates the accuracy of retinal pigment epithelium (RPE) atrophy progression as an outcome measure. METHODS: We performed a retrospective cohort study collecting multicenter data from 47 patients (91 eyes) with late-onset Stargardt, defined by clinical phenotype, at least one ABCA4 mutation, and age at disease onset ≥ 45 years. We analyzed RPE atrophy progression on fundus autofluorescence and near-infrared reflectance imaging using semiautomated software and a linear mixed model. We performed sample size calculations to assess the power in a simulated 2-year interventional study and assessed visual endpoints using time-to-event analysis. RESULTS: Over time, progression of RPE atrophy was observed (mean: 0.22 mm/year, 95% confidence interval [CI]: 0.19-0.27). By including only patients with bilateral RPE atrophy in a future trial, 32 patients are needed to reach a power of 83.9% (95% CI: 83.1-84.6), assuming a fixed therapeutic effect size of 30%. We found a median interval between disease onset and visual acuity decline to 20/32, 20/80, and 20/200 of 2.74 (95% CI: 0.54-4.41), 10.15 (95% CI: 6.13-11.38), and 11.38 (95% CI: 6.13-13.34) years, respectively. CONCLUSIONS: We show that RPE atrophy represents a robust biomarker to monitor disease progression in future therapeutic trials. In contrast, the variability in terms of the course of visual acuity was high.