Allele-Specific Chromosome Removal after Cas9 Cleavage in Human Embryos

Correction of disease-causing mutations in human embryos holds the potential to reduce the burden of inherited genetic disorders and improve fertility treatments for couples with disease-causing mutations in lieu of embryo selection. Here, we evaluate repair outcomes of a Cas9-induced double-strand break (DSB) introduced on the paternal chromosome at the EYS locus, which carries a frameshift mutation causing blindness. We show that the most common repair outcome is microhomology-mediated end joining, which occurs during the first cell cycle in the zygote, leading to embryos with non-mosaic restoration of the reading frame. Notably, about half of the breaks remain unrepaired, resulting in an undetectable paternal allele and, after mitosis, loss of one or both chromosomal arms. Correspondingly, Cas9 off-target cleavage results in chromosomal losses and hemizygous indels because of cleavage of both alleles. These results demonstrate the ability to manipulate chromosome content and reveal significant challenges for mutation correction in human embryos.

Therapy in Rhodopsin-Mediated Autosomal Dominant Retinitis Pigmentosa

Rhodopsin-mediated autosomal dominant retinitis pigmentosa (RHO-adRP) is a hereditary degenerative disorder in which mutations in the gene encoding RHO, the light-sensitive G protein-coupled receptor involved in phototransduction in rods, lead to progressive loss of rods and subsequently cones in the retina. Clinical phenotypes are diverse, ranging from mild night blindness to severe visual impairments. There is currently no cure for RHO-adRP. Although there have been significant advances in gene therapy for inherited retinal diseases, treating RHO-adRP presents a unique challenge since it is an autosomal dominant disease caused by more than 150 gain-of-function mutations in the RHO gene, rendering the established gene supplementation strategy inadequate. This review provides an update on RNA therapeutics and therapeutic editing genome surgery strategies and ongoing clinical trials for RHO-adRP, discussing mechanisms of action, preclinical data, current state of development, as well as risk and benefit considerations. Potential outcome measures useful for future clinical trials are also addressed.

Optical Gap Biomarker in Cone-Dominant Retinal Dystrophy

PURPOSE

To characterize the progression of optical gaps and expand the known etiologies of this phenotype.

DESIGN

Retrospective cohort study.

METHODS

Thirty-six patients were selected based on the identification of an optical gap on spectral-domain optical coherence tomography (OCT) from a large cohort of patients (N = 746) with confirmed diagnoses of inherited retinal dystrophy. The width and height of the gaps in 70 eyes of 36 patients were measured by 2 independent graders using the caliper tool on Heidelberg Explorer. Measurements of outer and central retinal thickness were also evaluated and correlated with gap dimensions.

RESULTS

Longitudinal analysis confirmed the progressive nature of optical gaps in patients with Stargardt disease, achromatopsia, occult macular dystrophy, and cone dystrophies (P < .003). Larger changes in gap width were noted in patients with Stargardt disease (78.1 μm/year) and cone dystrophies (31.9 μm/year) compared with patients with achromatopsia (16.2 μm/year) and occult macular dystrophy (15.4 μm/year). Gap height decreased in patients with Stargardt disease (6.5 μm/year; P = .02) but increased in patients with achromatopsia (3.3 μm/year) and occult macular dystrophy (1.2 μm/year). Gap height correlated with measurements of central retinal thickness at the fovea (r = 0.782, P = .00012). Interocular discordance of the gap was observed in 7 patients. Finally, a review of all currently described etiologies of optical gap was summarized.

CONCLUSION

The optical gap is a progressive phenotype seen in an increasing number of etiologies. This progressive nature suggests a use as a biomarker in the understanding of disease progression. Interocular discordance of the phenotype may be a feature of Stargardt disease and cone dystrophies.

A mutation in CRX causing pigmented paravenous retinochoroidal atrophy

INTRODUCTION

Mutations in the cone-rod homeobox (CRX) gene, a known cause of inherited retinal dystrophy, are characterized by extensive phenotypic heterogeneity. We describe a novel presentation of rod-cone dystrophy (RCD) phenocopying pigmented paravenous retinochoroidal atrophy associated with a mutation in CRX.

CASE DESCRIPTION

A 53-year-old man and his 48-year-old brother presented with a history of progressive vision loss and nyctalopia. Fundus examination revealed a bull's eye lesion with chorioretinal atrophy and intraretinal pigment migration, while spectral-domain optical coherence tomography (SD-OCT) demonstrated retinal thinning with outer retinal atrophy. On short-wavelength autofluorescence (SW-AF) imaging, an atypical paravenous pattern of atrophy with a surrounding hyperautofluorescent border was observed. Full-field electroretinogram (ffERG) revealed a rod-cone pattern of dysfunction. A heterozygous pathogenic variant, c.119G>A:p.(Arg40Gln), in the CRX gene was identified in both brothers and segregated in their family.

CONCLUSION

This case report broadens the currently known phenotypic presentations of CRX-associated retinopathy and suggests that mutations in CRX may be associated with pigmented paravenous retinochoroidal atrophy.

Differences in Intraretinal Pigment Migration Across Inherited Retinal Dystrophies

PURPOSE

To determine whether there are differences in the prevalence of intraretinal pigment migration (IPM) across ages and genetic causes of inherited retinal dystrophies (IRDs).

DESIGN

Retrospective cohort study.

METHODS

Patients were evaluated at a single tertiary referral center. All patients with a clinical diagnosis of IRD and confirmatory genetic testing were included in these analyses. A total of 392 patients fit inclusion criteria, and 151 patients were excluded based on inconclusive genetic testing. Patients were placed into 3 groups, ciliary and ciliary-related photoreceptor, nonciliary photoreceptor, and retinal pigment epithelium (RPE), based on the cellular expression of the gene and the primary affected cell type. The presence of IPM was evaluated by using slit lamp biomicroscopy, indirect ophthalmoscopy, and wide-field color fundus photography.

RESULTS

IPM was seen in 257 of 339 patients (75.8%) with mutations in photoreceptor-specific genes and in 18 of 53 patients (34.0%) with mutations in RPE-specific genes (P < .0001). Pairwise analysis following stratification by age and gene category suggested significant differences at all age groups between patients with mutations in photoreceptor-specific genes and patients with mutations in RPE-specific genes (P < .05). A fitted multivariate logistic regression model was produced and demonstrated that the incidence of IPM increases as a function of both age and gene category.

CONCLUSIONS

IPM is a finding more commonly observed in IRDs caused by mutations in photoreceptor-specific genes than RPE-specific genes. The absence of IPM does not always rule out IRD and should raise suspicion for disease mutations in RPE-specific genes.

Quantitative Fundus Autofluorescence in HCQ Retinopathy

Purpose

To increase our understanding of the mechanisms underlying hydroxychloroquine (HCQ) retinopathy, analyses by quantitative fundus autofluorescence (qAF) and near-infrared fundus autofluorescence (NIR-AF) were compared to results obtained by recommended screening tests.

Methods

Thirty-one patients (28 females, 3 males) were evaluated with standard automated perimetry and spectral domain optical coherence tomography (SD-OCT); 28 also had multifocal electroretinography (mfERG). Measurement of short-wavelength fundus autofluorescence (SW-AF) by qAF involved the use of an internal fluorescent reference and intensity measurements in eight concentric segments at 7° to 9° eccentricity. For semiquantitative analysis of NIR-AF, intensities were acquired along a vertical axis through the fovea.

Results

Four of 15 high-dose (total dose >1000 g, daily dose >5.0 mg/kg) patients and one of 16 low-dose (total dose <1000 g, daily dose 4.4 mg/kg) patients were diagnosed with HCQ-associated retinopathy based on abnormal 10-2 visual fields, SD-OCT, and SW-AF imaging. Three of the high-dose patients also had abnormal mfERG results. Of the five patients exhibiting retinopathy, two had qAF color-coded images revealing higher intensities inferior, nasal, and lateral to the fovea. The abnormal visual fields also exhibited superior-inferior differences. Mean NIR-AF gray-level intensities were increased in four high-dose patients with no evidence of retinopathy. In two patients with retinopathy, NIR-AF intensity within the parafovea was below the normal range. One high-dose patient (6.25 mg/kg) had only abnormal mfERG results.

Conclusions

These findings indicate that screening for HCQ retinopathy should take into consideration superior-inferior differences in susceptibility to HCQ retinopathy.

Progressive Choriocapillaris Impairment in ABCA4 Maculopathy Is Secondary to Retinal Pigment Epithelium Atrophy

Purpose

To analyze the progression of choriocapillaris (CC) impairment in recessive Stargardt disease (STGD) and compare it to the progression of retinal pigment epithelium (RPE) atrophy.

Methods

Fifty-five patients with a clinical diagnosis of STGD and genetic confirmation of pathogenic biallelic variants in ABCA4 were imaged with short-wavelength fundus autofluorescence (SW-AF) and optical coherence tomography angiography (OCTA) at a single clinic visit, whereas a subset of 12 patients were imaged with the same modalities at two different clinic visits.

Results

We observed three stages of CC impairment: an area of bright yet intact macular CC (11 patients), regions of vascular rarefaction and incomplete CC atrophy within an area of bright CC (10 patients), and areas of extensive CC atrophy (26 patients). These changes correlated to the degree of RPE atrophy observed in SW-AF imaging. Furthermore, 8 patients presented with early changes on SW-AF, but healthy CC. Quantitative analyses of the atrophic changes revealed that the area of RPE atrophy is larger (9.6 ± 1.7 mm2 vs. 6.9 ± 1.3 mm2, P < 0.001) and that it progresses at a faster rate (1.1 ± 0.1 mm2/year vs. 0.8 ± 0.2 mm2/year, P = 0.004) than the corresponding area of CC atrophy.

Conclusions

CC impairment is progressive and OCTA imaging can be used to demonstrate the stages, which culminate in extensive CC atrophy. Furthermore, CC impairment is secondary to RPE atrophy in STGD. We further advocate the use of SW-AF and OCTA imaging in monitoring the progression of STGD.

Spectral-Domain Optical Coherence Tomography Is More Sensitive for Hydroxychloroquine-Related Structural Abnormalities Than Short-Wavelength and Near-Infrared Autofluorescence

Purpose

To analyze the appearance of structural abnormalities due to hydroxychloroquine (HCQ) toxicity by spectral-domain optical coherence tomography (SD-OCT) and short-wavelength autofluorescence (SW-AF) and near-infrared fundus autofluorescence (NIR-AF) imaging.

Methods

This retrospective cohort study included 88 eyes from 44 patients who had a history of or were currently taking HCQ. SD-OCT, SW-AF, and NIR-AF images were analyzed by two independent graders for the detection of HCQ-associated abnormalities.

Results

Sixty eyes (30 patients, 68%) presented with no abnormalities for either imaging modality. Twenty eyes (10 patients, 23%) presented with parafoveal abnormalities (ellipsoid zone attenuation and/or interdigitation zone continuity loss) in SD-OCT scans but with qualitatively normal SW-AF and NIR-AF images. Eight eyes (four patients, 9%) presented with bull's-eye maculopathy in SW-AF and NIR-AF images, with corresponding outer retinal structures disrupted parafoveally in SD-OCT scans ("flying saucer" sign). No patients presented with normal SD-OCT scans and concurrent abnormalities in SW-AF or NIR-AF images.

Conclusions

SD-OCT was more sensitive in detecting structural abnormalities than either SW-AF or NIR-AF imaging, suggesting its superiority as a screening imaging modality for HCQ toxicity. Maculopathy and abnormalities in the retinal pigment epithelium from HCQ toxicity can be appreciated in both SW-AF and NIR-AF images.

Translational Relevance

Although debate exists regarding the best imaging modalities for screening patients for potential HCQ toxicity, our study supports the use of SD-OCT over both SW-AF and NIR-AF imaging as a screening modality.

HMGB1 and Caveolin-1 related to RPE cell senescence in age-related macular degeneration

Accumulation of lipofuscin in the retinal pigment epithelium (RPE) is considered a major cause of RPE dysfunction and senescence in age-related macular degeneration (AMD), and N-retinylidene-N-retinylethanolamine (A2E) is the main fluorophore identified in lipofuscin from aged human eyes. Here, human-induced pluripotent stem cell (iPSC)-RPE was generated from healthy individuals to reveal proteomic changes associated with A2E-related RPE cell senescence. A novel RPE cell senescence-related protein, high-mobility group box 1 (HMGB1), was identified based on proteomic mass spectrometry measurements on iPSC-RPE with A2E treatment. Furthermore, HMGB1 upregulated Caveolin-1, which also was related RPE cell senescence. To investigate whether changes in HMGB1 and Caveolin-1 expression under A2E exposure contribute to RPE cell senescence, human ARPE-19 cells were stimulated with A2E; expression of HMGB1, Caveolin-1, tight junction proteins and senescent phenotypes were verified. HMGB1 inhibition alleviated A2E induced cell senescence. Migration of RPE cells was evaluated. Notably, A2E less than or equal to 10μM induced both HMGB1 and Caveolin-1 protein upregulation and HMGB1 translocation, while Caveolin-1 expression was downregulated when there was more than 10μM A2E. Our data indicate that A2E-induced upregulation of HMGB1、Caveolin-1 and HMGB1 release may relate to RPE cell senescence and play a role in the pathogenesis of AMD.

Sequential multiple retinal vein occlusions and transient ischemic attack in MTHFR polymorphism and protein S deficiency

BACKGROUND

The C677T variant of the MTHFR (5,10-Methylenetetrahydrofolate reductase) gene is associated with increased susceptibility to homocystinuria (OMIM#236250), neural tube defects (OMIM#601634), schizophrenia (OMIM#181500), thromboembolism (OMIM#188050), and vascular diseases. Protein S deficiency is also associated with an increased risk of thromboembolism from reduced thrombin generation. In this report, we describe the case of a patient who presented with multiple retinal vein occlusions likely caused by an underlying combination of a homozygous MTHFR C677T variant and protein S deficiency.

METHODS

We performed 8 years of continuous ophthalmic follow-up of one patient diagnosed with central retinal vein occlusion. Peripheral blood was collected for metabolic evaluation and hypercoagulability assessment. Targeted gene sequencing was used for genetic diagnosis. Examination of the retinal vasculature was performed through dilated funduscopic examination, digital color fundus and ultrawide-field color fundus photography, spectral domain optical coherence tomography, and fluorescein angiography.

RESULTS

Sequential retinal vein occlusions and a transient ischemic attack were observed during the follow-up period. Targeted gene sequencing by PCR identified the homozygous MTHFR C677T variant. The metabolic profile indicated low-protein S activity, high levels of vitamin B6, and LDL cholesterol consistent with her hypercoagulable state. Prescription of low-dose aspirin and atorvastatin for hypercholesterolemia resulted in no further neovascularization, leakage, or vein occlusion.

CONCLUSION

Retinal vein occlusions associated with the MTHFR C677T variant and protein S deficiency may signal impending systemic thromboembolic episodes and warrant aggressive preventative measures.

Optical coherence tomography in the evaluation of retinitis pigmentosa

BACKGROUND

Optical coherence tomography (OCT) is a non-invasive imaging test that provides easily obtainable and highly reproducible cross-sectional images of the retina. Improved modalities of the OCT that are capable of providing high quality images of not only the retina, but also the deeper structures and vasculature have been developed, including swept-source OCTs and OCT angiography.

MATERIALS AND METHODS

Review.

RESULTS

The use of OCT in the monitoring of retinitis pigmentosa has been well described and numerous signs of disease progression have been studied. Notably among them are the detection of changes to retinal thickness, the ellipsoid zone, the vasculature on OCT angiography, and cystoid macular edema.

CONCLUSION

In this review, we discuss the multiple applications of OCT as a tool in the monitoring of retinitis pigmentosa and its potential use as an outcome measurement in current and future therapeutic endeavors.

Hypoxic drive caused type 3 neovascularization in a preclinical model of exudative age-related macular degeneration

Hypoxia associated with the high metabolic demand of rods has been implicated in the pathology of age-related macular degeneration (AMD), the most common cause of adult blindness in the developed world. The majority of AMD-associated severe vision loss cases are due to exudative AMD, characterized by neovascularization. To further investigate the causes and histopathology of exudative AMD, we conditionally induced hypoxia in a novel preclinical AMD model (Pde6gcreERT2/+;Vhl-/-) by targeting Vhl and used multimodal imaging and immunohistochemistry to track the development of hypoxia-induced neovascularization. In addition to developing a preclinical model that phenocopies exudative AMD, our studies revealed that the photoreceptor hypoxic response initiates and drives type 3 neovascularization, mainly in the outer retina. Activation of the VHL-HIF1a-VEGF-EPO pathway in the adult retina led to long-term neovascularization, retinal hemorrhages and compromised retinal layers. Our novel preclinical model would accelerate the testing of therapies that use metabolomic approaches to ameliorate AMD.

PKM2 ablation enhanced retinal function and survival in a preclinical model of retinitis pigmentosa

Retinitis pigmentosa (RP) is a neurodegenerative disorder that causes irreversible vision loss in over 1.5 million individuals world-wide. The genetic heterogeneity of RP necessitates a broad therapy that is able to provide treatment in a gene- and mutation- non-specific manner. In this study, we identify the therapeutic benefits of metabolic reprogramming by targeting pyruvate kinase M2 (PKM2) in a Pde6β preclinical model of RP. The genetic contributions of PKM2 inhibition in retinal degeneration were evaluated through histology and electroretinogram (ERG) followed by a statistical analysis using a linear regression model. Notably, PKM2 ablation resulted in thicker retinal layers in Pde6β-mutated mice as compared to the controls, suggesting greater photoreceptor survival. Consistent with these anatomical findings, ERG analyses revealed that the maximum b-wave is on average greater in Pkm2 knockout mice than in mice with intact Pkm2, indicating enhanced photoreceptor function. These rescue phenotypes from Pkm2 ablation in a preclinical model of RP indicate that a metabolome reprogramming may be useful in treating RP.

Comparative Analysis of Functional and Structural Decline in Retinitis Pigmentosas

Retinitis pigmentosa (RP) is a category of inherited retinal dystrophies that is best prognosticated using electroretinography (ERG). In this retrospective cohort study of 25 patients with RP, we evaluated the correlation between 30 Hz flicker ERG and structural parameters in the retina. Internationally standardized 30 Hz flicker ERG recordings, short-wavelength autofluorescence (SW-AF), and spectral domain–optical coherence tomography (SD-OCT) were acquired at two visits at least one year apart. Vertical and horizontal hyperautofluorescent ring diameter measurements with SW-AF, as well as ellipsoid zone (EZ) line width measurements with SD-OCT, were used as structural parameters of disease progression. The 30 Hz flicker ERG amplitude decreased by 2.2 ± 0.8 µV/year (p = 0.011), while implicit times remained unchanged. For SD-OCT, the EZ line decreased by 204.1 ± 34.7 µm/year (p < 0.001). Horizontal and vertical hyperautofluorescent ring diameters decreased by 161.9 ± 25.6 µm/year and 146.9 ± 34.6 µm/year, respectively (p = 0.001), with SW-AF. A correlation was found between the progression rates of the 30 Hz flicker amplitude recorded with Burian–Allen electrodes and both the horizontal ring diameter (p = 0.020) and EZ line (p = 0.044). SW-AF and SD-OCT, two readily available imaging techniques, may be used to prognosticate disease progression because of the reliability of their measurements and correlation with functional outcome.

Multiexon deletion alleles of ATF6 linked to achromatopsia

Achromatopsia (ACHM) is an autosomal recessive disease that results in severe visual loss. Symptoms of ACHM include impaired visual acuity, nystagmus, and photoaversion starting from infancy; furthermore, ACHM is associated with bilateral foveal hypoplasia and absent or severely reduced cone photoreceptor function on electroretinography. Here, we performed genetic sequencing in 3 patients from 2 families with ACHM, identifying and functionally characterizing 2 mutations in the activating transcription factor 6 (ATF6) gene. We identified a homozygous deletion covering exons 8-14 of the ATF6 gene from 2 siblings from the same family. In another patient from a different family, we identified a heterozygous deletion covering exons 2 and 3 of the ATF6 gene found in trans with a previously identified ATF6 c.970C>T (p.Arg324Cys) ACHM disease allele. Recombinant ATF6 proteins bearing these exon deletions showed markedly impaired transcriptional activity by qPCR and RNA-Seq analysis compared with WT-ATF6. Finally, RNAscope revealed that ATF6 and the related ATF6B transcripts were expressed in cones as well as in all retinal layers in normal human retina. Overall, our data identify loss-of-function ATF6 disease alleles that cause human foveal disease.

Effects of deficiency in the RLBP1-encoded visual cycle protein CRALBP on visual dysfunction in humans and mice

Mutations in retinaldehyde-binding protein 1 (RLBP1), encoding the visual cycle protein cellular retinaldehyde-binding protein (CRALBP), cause an autosomal recessive form of retinal degeneration. By binding to 11-cis-retinoid, CRALBP augments the isomerase activity of retinoid isomerohydrolase RPE65 (RPE65) and facilitates 11-cis-retinol oxidation to 11-cis-retinal. CRALBP also maintains the 11-cis configuration and protects against unwanted retinaldehyde activity. Studying a sibling pair that is compound heterozygous for mutations in RLBP1/CRALBP, here we expand the phenotype of affected individuals, elucidate a previously unreported phenotype in RLBP1/CRALBP carriers, and demonstrate consistencies between the affected individuals and Rlbp1/Cralbp^−/− mice. In the RLBP1/CRALBP-affected individuals, nonrecordable rod-specific electroretinogram traces were recovered after prolonged dark adaptation. In ultrawide-field fundus images, we observed radially arranged puncta typical of RLBP1/CRALBP-associated disease. Spectral domain-optical coherence tomography (SD-OCT) revealed hyperreflective aberrations within photoreceptor-associated bands. In short-wavelength fundus autofluorescence (SW-AF) images, speckled hyperautofluorescence and mottling indicated macular involvement. In both the affected individuals and their asymptomatic carrier parents, reduced SW-AF intensities, measured as quantitative fundus autofluorescence (qAF), indicated chronic impairment in 11-cis-retinal availability and provided information on mutation severity. Hypertransmission of the SD-OCT signal into the choroid together with decreased near-infrared autofluorescence (NIR-AF) provided evidence for retinal pigment epithelial cell (RPE) involvement. In Rlbp1/Cralbp^−/− mice, reduced 11-cis-retinal levels, qAF and NIR-AF intensities, and photoreceptor loss were consistent with the clinical presentation of the affected siblings. These findings indicate that RLBP1 mutations are associated with progressive disease involving RPE atrophy and photoreceptor cell degeneration. In asymptomatic carriers, qAF disclosed previously undetected visual cycle deficiency.

Perspectives on Gene Therapy: Choroideremia Represents a Challenging Model for the Treatment of Other Inherited Retinal Degenerations

Purpose

To report combined viewpoints on ocular gene therapy from a select group of clinician scientists and a patient advocacy group.

Methods

With the support of Randy Wheelock and Dr. Chris Moen from the Choroideremia Research Foundation (CRF), a special interest group at the 2019 Annual meeting of the Association for Research in Vision and Ophthalmology in Vancouver, Canada, shared their knowledge, experience, concepts, and ideas and provided a forum to discuss therapeutic strategies for the treatment of inherited retinal disorders, using experience in choroideremia (CHM) as a model.

Results

A member of the CRF presented the patient perspective and role in clinical trials. Five clinician scientists presented reasons for limited long-term visual improvement in many gene therapy trials, including challenges with dose, incomplete understanding of photoreceptor metabolism, vector delivery, inflammation, and identification of patients likely to benefit from treatment.

Conclusions

The shared experience of the five clinician scientists indicates that the results of ocular gene therapy for choroideremia have been less successful than for RPE65-related Leber congenital amaurosis. Improvement in vector delivery and developing a better understanding of gene expression in target tissues, treatment dose and side effects, and inflammation, as well as identifying patients who are most likely to benefit without suffering excessive risk, are necessary to advance the development of effective therapies for inherited retinal degenerations.

Translational Relevance

Additional long-term data are required to determine if ocular gene therapy will be sufficient to alter natural progression in choroideremia. Combination therapies may have to be considered, as well as alternative vectors that minimize risk.

Phenotypic expansion of autosomal dominant retinitis pigmentosa associated with the D477G mutation in RPE65

Mutations in the gene RPE65 (OMIM: 180069) are recessively inherited and known to cause Leber congenital amaurosis. Recently, the mutation D477G in RPE65 has been identified as a cause of autosomal dominant retinitis pigmentosa (RP). Variable expressivity of this disease has been reported, as carrier individuals can present with mild, nonpenetrant, or, most commonly, a severe chorioretinal phenotype that resembles choroideremia. We report the case of a 57-yr-old male who presented to our clinic with nyctalopia and decreasing visual acuity for 1 yr. Dilated fundus examination revealed retinal atrophy and peripheral mottling of the retinal pigment epithelium (RPE). SW-AF revealed patchy hypoautofluorescence throughout the posterior pole with separate lacunae-like areas in the macula of severe RPE atrophy along with foveal sparing. Full-field electroretinogram suggested a rod-cone dystrophy. Whole-exome sequencing revealed the heterozygous mutation c.1430A > G (p.D477G) in the RPE65 gene. This phenotype of peripheral RPE mottling and severe macular lacunae-like atrophy has not been previously reported with RPE65 autosomal dominant RP, supporting the variable expressivity of the disease and expanding the known phenotypic presentations.

Progressive RPE atrophy and photoreceptor death in KIZ-associated autosomal recessive retinitis pigmentosa

Background: To evaluate the long-term progression of autosomal recessive retinitis pigmentosa (RP) due to mutations in KIZ using multimodal imaging and a quantitative analytical approach.Methods: Whole exome sequencing (WES) and targeted capture sequencing were used to identify mutation. Fundus photography, short-wavelength autofluorescence (SW-AF), spectral-domain optical coherence tomography (SD-OCT) imaging, and electroretinography (ERG) were analyzed. Serial measurements of peripheral retinal pigment epithelium (RPE) atrophy area with SW-AF, as well as the ellipsoid zone (EZ) width using SD-OCT were performed.Results: Two homozygous variants in KIZ-a c.226C>T mutation as well as a previously unreported c.119_122delAACT mutation-were identified in four unrelated patients. Fundus examination and ERG revealed classic rod-cone dysfunction, and SD-OCT demonstrated outer retinal atrophy with centrally preserved EZ line. SW-AF imaging revealed hyperautofluorescent rings with surrounding parafoveal, mid-peripheral and widespread loss of autofluorescence. The RPE atrophy area increased annually by 4.9%. Mean annual exponential rates of decline for KIZ patients were 8.5% for visual acuity and 15.9% for 30 Hz Flicker amplitude. The average annual reduction distance of the EZ distance was 66.5 μm per year.Conclusions: RPE atrophy progresses along with a loss of photoreceptors, and parafoveal RPE hypoautofluorescence is commonly seen in KIZ-associated RP patients. KIZ-associated RP is an early-onset severe rod-cone dystrophy.

Fundoscopy-directed genetic testing to re-evaluate negative whole exome sequencing results

Background

Whole exome sequencing (WES) allows for an unbiased search of the genetic cause of a disease. Employing it as a first-tier genetic testing can be favored due to the associated lower incremental cost per diagnosis compared to when using it later in the diagnostic pathway. However, there are technical limitations of WES that can lead to inaccurate negative variant callings. Our study presents these limitations through a re-evaluation of negative WES results using subsequent tests primarily driven by fundoscopic findings. These tests included targeted gene testing, inherited retinal gene panels, whole genome sequencing (WGS), and array comparative genomic hybridization.

Results

Subsequent genetic testing guided by fundoscopy findings identified the following variant types causing retinitis pigmentosa that were not detected by WES: frameshift deletion and nonsense variants in the RPGR gene, 353-bp Alu repeat insertions in the MAK gene, and large exonic deletion variants in the EYS and PRPF31 genes. Deep intronic variants in the ABCA4 gene causing Stargardt disease and the GUCY2D gene causing Leber congenital amaurosis were also identified.

Conclusions

Negative WES analyses inconsistent with the phenotype should raise clinical suspicion. Subsequent genetic testing may detect genetic variants missed by WES and can make patients eligible for gene replacement therapy and upcoming clinical trials. When phenotypic findings support a genetic etiology, negative WES results should be followed by targeted gene sequencing, array based approach or whole genome sequencing.

Inhibition of Ca2+ channel surface expression by mutant bestrophin-1 in RPE cells

The BEST1 gene product bestrophin-1, a Ca²⁺ -dependent anion channel, interacts with Ca_V 1.3 Ca²⁺ channels in the retinal pigment epithelium (RPE). BEST1 mutations lead to Best vitelliform macular dystrophy. A common functional defect of these mutations is reduced trafficking of bestrophin-1 into the plasma membrane. We hypothesized that this defect affects the interaction partner Ca_V 1.3 channel affecting Ca²⁺ signaling and altered RPE function. Thus, we investigated the protein interaction between Ca_V 1.3 channels and bestrophin-1 by immunoprecipitation, Ca_V 1.3 activity in the presence of mutant bestrophin-1 and intracellular trafficking of the interaction partners in confluent RPE monolayers. We selected four BEST1 mutations, each representing one mutational hotspot of the disease: T6P, F80L, R218C, and F305S. Heterologously expressed L-type channels and mutant bestrophin-1 showed reduced interaction, reduced Ca_V 1.3 channel activity, and changes in surface expression. Transfection of polarized RPE (porcine primary cells, iPSC-RPE) that endogenously express Ca_V 1.3 and wild-type bestrophin-1, with mutant bestrophin-1 confirmed reduction of Ca_V 1.3 surface expression. For the four selected BEST1 mutations, presence of mutant bestrophin-1 led to reduced Ca_V 1.3 activity by modulating pore-function or decreasing surface expression. Reduced Ca_V 1.3 activity might open new ways to understand symptoms of Best vitelliform macular dystrophy such as reduced electro-oculogram, lipofuscin accumulation, and vision impairment.

Patterns and Intensities of Near-Infrared and Short-Wavelength Fundus Autofluorescence in Choroideremia Probands and Carriers

Purpose

To ascertain cellular constituents within islands of preserved retina in choroideremia (CHM) by multimodal imaging.

Methods

CHM probands (16) and female carriers (9) of CHM were studied. Near-infrared autofluorescence (NIR-AF; 787-nm excitation; emission, >830 nm), short-wavelength autofluorescence (SW-AF; 488-nm excitation, 500- to 680-nm emission), and spectral-domain optical coherence tomography (SD-OCT) images were acquired with a confocal scanning laser ophthalmoscope. SW-AF intensities were measured by quantitative fundus autofluorescence (qAF), and NIR-AF intensity profiles were analyzed. Retinal thicknesses and visual acuity were measured.

Results

In 19 of 31 eyes of affected males, islands of preserved NIR-AF signal were also visible as fluorescence signal in SW-AF images. Notable in 12 eyes were areas of speckled SW-AF that was hypoautofluorescent in the NIR-AF image. Islands of preserved NIR-AF and SW-AF signal were often associated with the presence of visible but thinned outer nuclear layer and discontinuous interdigitation zone, ellipsoid zone, and external limiting membrane. NIR-AF profiles revealed that even in areas of preserved retina, the NIR-AF signal from retinal pigment epithelium (RPE) melanin is greatly reduced. qAF was reduced overall. The fundus of carriers was characterized by a mosaicism in which patches of reduced NIR-AF colocalized with reduced SW-AF.

Conclusions

In CHM-affected males, the presence of RPE was indicated by an NIR-AF signal and the absence of hypertransmission of OCT signal into the choroid. RPE preservation was associated with better visual acuity. In carriers, patches of reduced SW-AF colocalized with decreased NIR-AF and qAF was severely reduced.