Gene Supplementation in Mice Heterozygous for the D477G-RPE65 Variant Implicated in Autosomal Dominant Retinitis Pigmentosa

The use of AAV-RPE65 vectors for gene supplementation has achieved spectacular success as a treatment for individuals with autosomal recessive retinal disease (arRD) caused by biallelic mutations in the visual cycle gene RPE65. However, the efficacy of this approach in treating autosomal dominant retinitis pigmentosa (adRP) associated with a monoallelic mutation encoding a rare D477G RPE65 variant has not been studied. Although lacking a severe phenotype, we now find that knock-in mice heterozygous for D477G RPE65 (D477G KI mice) can be used to evaluate outcomes of AAV-RPE65 gene-supplementation. Total RPE65 protein levels, which are decreased in heterozygous D477G KI mice, were doubled following subretinal delivery of rAAV2/5.hRPE65p.hRPE65. In addition, rates of recovery of the chromophore 11-cis retinal after bleaching were significantly increased in eyes that received AAV-RPE65, consistent with increased RPE65 isomerase activity. While dark-adapted chromophore levels and a-wave amplitudes were not affected, b-wave recovery rates were modestly improved. The present findings establish that gene supplementation enhances 11-cis retinal synthesis in heterozygous D477G KI mice, and complement previous studies showing that chromophore therapy results in improved vision in individuals with adRP associated with D477G RPE65.

A Mouse Model with Ablated Asparaginase and Isoaspartyl Peptidase 1 (Asrgl1) Develops Early Onset Retinal Degeneration (RD) Recapitulating the Human Phenotype

We previously identified a homozygous G178R mutation in human ASRGL1 (hASRGL1) through whole-exome analysis responsible for early onset retinal degeneration (RD) in patients with cone-rod dystrophy. The mutant G178R ASRGL1 expressed in Cos-7 cells showed altered localization, while the mutant ASRGL1 in E. coli lacked the autocatalytic activity needed to generate the active protein. To evaluate the effect of impaired ASRGL1 function on the retina in vivo, we generated a mouse model with c.578_579insAGAAA (NM_001083926.2) mutation (Asrgl1mut/mut) through the CRISPR/Cas9 methodology. The expression of ASGRL1 and its asparaginase activity were undetectable in the retina of Asrgl1mut/mut mice. The ophthalmic evaluation of Asrgl1mut/mut mice showed a significant and progressive decrease in scotopic electroretinographic (ERG) response observed at an early age of 3 months followed by a decrease in photopic response around 5 months compared with age-matched wildtype mice. Immunostaining and RT-PCR analyses with rod and cone cell markers revealed a loss of cone outer segments and a significant decrease in the expression of Rhodopsin, Opn1sw, and Opn1mw at 3 months in Asrgl1mut/mut mice compared with age-matched wildtype mice. Importantly, the retinal phenotype of Asrgl1mut/mut mice is consistent with the phenotype observed in patients harboring the G178R mutation in ASRGL1 confirming a critical role of ASRGL1 in the retina and the contribution of ASRGL1 mutations in retinal degeneration.

Adherence and satisfaction in Argus II prosthesis users: a self determination theory model

BACKGROUND

Self-determination theory (SDT) of human motivation was used to examine associations between different forms of motivation in Argus II retinal prosthesis users and their engagement and satisfaction with the Argus device.

MATERIALS AND METHODS

Nine subjects were administered: 1) a Situational Motivation Scale (SIMS) questionnaire to measure intrinsic motivation, identified regulation, external regulation, and amotivation, and 2) the Argus questionnaire (AQ) which was organized into 5 categories to measure 'Decision to get an Argus implant,' 'Self-perception as an Argus user', 'Utility of Argus,' 'Perceived competence,' and 'Family support.' Spearman correlations (r_s) were used to find associations between measures from SIMS and AQ.

RESULTS

Nine subjects completed both questionnaires. Statistically significant associations were observed between identified regulation and AQ items from categories: Decision to get Argus, Self-perception, Utility of Argus, and Perceived competence; and between intrinsic motivation and AQ items from Self-perception and Utility. External regulation was negatively associated with Family support, and amotivation was associated with one item from Self-perception. Engagement with the device and satisfaction were associated to both identified regulation and intrinsic motivation. There was no significant relationship between external regulation and adherence to the device.

CONCLUSIONS

The SDT model can be used to investigate the types of motivation that influence uptake and engagement of the Argus device. Clinicians can use this knowledge to improve outcomes by supporting confidence in users and by encouraging them to maintain internalization and continued commitment to adherence.

Deciphering the genetic architecture and ethnographic distribution of IRD in three ethnic populations by whole genome sequence analysis

Patients with inherited retinal dystrophies (IRDs) were recruited from two understudied populations: Mexico and Pakistan as well as a third well-studied population of European Americans to define the genetic architecture of IRD by performing whole-genome sequencing (WGS). Whole-genome analysis was performed on 409 individuals from 108 unrelated pedigrees with IRDs. All patients underwent an ophthalmic evaluation to establish the retinal phenotype. Although the 108 pedigrees in this study had previously been examined for mutations in known IRD genes using a wide range of methodologies including targeted gene(s) or mutation(s) screening, linkage analysis and exome sequencing, the gene mutations responsible for IRD in these 108 pedigrees were not determined. WGS was performed on these pedigrees using Illumina X10 at a minimum of 30X depth. The sequence reads were mapped against hg19 followed by variant calling using GATK. The genome variants were annotated using SnpEff, PolyPhen2, and CADD score; the structural variants (SVs) were called using GenomeSTRiP and LUMPY. We identified potential causative sequence alterations in 61 pedigrees (57%), including 39 novel and 54 reported variants in IRD genes. For 57 of these pedigrees the observed genotype was consistent with the initial clinical diagnosis, the remaining 4 had the clinical diagnosis reclassified based on our findings. In seven pedigrees (12%) we observed atypical causal variants, i.e. unexpected genotype(s), including 4 pedigrees with causal variants in more than one IRD gene within all affected family members, one pedigree with intrafamilial genetic heterogeneity (different affected family members carrying causal variants in different IRD genes), one pedigree carrying a dominant causative variant present in pseudo-recessive form due to consanguinity and one pedigree with a de-novo variant in the affected family member. Combined atypical and large structural variants contributed to about 20% of cases. Among the novel mutations, 75% were detected in Mexican and 50% found in European American pedigrees and have not been reported in any other population while only 20% were detected in Pakistani pedigrees and were not previously reported. The remaining novel IRD causative variants were listed in gnomAD but were found to be very rare and population specific. Mutations in known IRD associated genes contributed to pathology in 63% Mexican, 60% Pakistani and 45% European American pedigrees analyzed. Overall, contribution of known IRD gene variants to disease pathology in these three populations was similar to that observed in other populations worldwide. This study revealed a spectrum of mutations contributing to IRD in three populations, identified a large proportion of novel potentially causative variants that are specific to the corresponding population or not reported in gnomAD and shed light on the genetic architecture of IRD in these diverse global populations.

The study was performed to identify the underlying cause of inherited retinal degeneration (IRD) in 409 individuals from 108 families. Primarily, these families were recruited from three different geographic regions: Mexico, Pakistan and European Americans from the United States. Blood samples were collected from all individuals for genome analysis. This analysis detected causative variants in 61 out of the 108 pedigrees. A total of 93 gene variants were found in the 61 families. Among these, 54 were previously reported as causative variants and the remaining 39 have not been reported in IRD pedigrees. Interestingly, 54% of these novel variants were not listed in gnomAD. In addition to these findings, complex causative genotypes were observed in 20% of pedigrees. Overall, causative variants were detected in 63% Mexican, 60% Pakistani and 45% European American pedigrees. This study revealed the distribution of IRD causative variants in pedigrees with diverse ethnic and geographic backgrounds.

Calculation of test-retest variability in phase I/IIa clinical trials for Inherited Retinal Degenerations

Background: Several novel treatments of inherited retinal degenerations have undergone phase I/IIa clinical trials with limited sample size, yet investigators must still determine if toxicity or an efficacy signal occurred or if the change was due to test-retest variability (TRV) of the measurement tool.Materials and Methods: Synthetic datasets were used to compare three types of TRV estimators under different sample sizes, mean drift, skewness, and number of baseline measurements.Results: Mixed effects models underestimated the standard deviation of measurement error (SDEM); the unbiased change score estimator method (UBS) was more accurate. The fixed effect model had less bias and smaller standard deviation than UBS if >2 baseline measurements. The change score estimator had no bias; other estimators introduced bias for lower variability. With sample size <10, all estimators had high variance. With sample size ≥10, the differences between methods were often minimal. The pooled estimator model did not capture drift, whereas a fixed effect regression or mixed effects models accounted for drift while maintaining an accurate measure of variance. With small sample sizes, the bootstrap estimates of SDEM were severe underestimates, while the jackknife estimates were mildly low but much better. The jackknife was more accurate for the unbiased change score method than for the pooled estimator.Conclusions: The ideal phase I/IIa study has ≥20 subjects and uses UBS or its fixed effect model generalization if >2 baseline measurements. With non-ideal study parameters, investigators should at least quantify the error estimate present in their data analysis.

The RUSH2A Study: Best-Corrected Visual Acuity, Full-Field Electroretinography Amplitudes, and Full-Field Stimulus Thresholds at Baseline

Purpose

The purpose of this study was to evaluate baseline best corrected visual acuity (BCVA), full-field electroretinography (ERG), full-field stimulus thresholds (FST), and their relationship with baseline demographic and clinical characteristics in the Rate of Progression in Usher syndrome type 2 (USH2A)-related Retinal Degeneration (RUSH2A) multicenter study.

Methods

Participants had Usher syndrome type 2 (USH2, N = 80) or autosomal recessive nonsyndromic retinitis pigmentosa (ARRP, N = 47) associated with biallelic variants in the USH2A gene. Associations of demographic and clinical characteristics with BCVA, ERG, and FST were assessed with regression models.

Results

In comparison to ARRP, USH2 had worse BCVA (median 79 vs. 82 letters; P < 0.001 adjusted for age), lower rod-mediated ERG b-wave amplitudes (median 0.0 vs. 6.6 µV; P < 0.001) and 30 Hz flicker cone-mediated ERG amplitudes (median 1.5 vs. 3.1 µV; P = 0.001), and higher (white, blue, and red) FST thresholds (means [−26, −31, −23 dB] vs. [−39, −45, −28 dB]; P < 0.001 for all stimuli). After adjusting for age, gender, and duration of vision loss, the difference in BCVA between diagnosis groups was attenuated (P = 0.09). Only diagnosis was associated with rod- and cone-mediated ERG parameters, whereas both genders (P = 0.04) and duration of visual loss (P < 0.001) also were associated with FST white stimulus.

Conclusions

USH2 participants had worse BCVA, ERG, and FST than ARRP participants. FST was strongly associated with duration of disease; it remains to be determined whether it will be a sensitive measure of progression.

Translational Relevance

Using standardized research protocols in RUSH2A, measures have been identified to monitor disease progression and treatment response and differentiate features of prognostic relevance between USH2 and ARRP participants with USH2A mutations.

Rapid visual field constriction in a patient with retinitis pigmentosa and pituitary adenoma

PURPOSE

To report a case of pituitary adenoma in a patient with retinitis pigmentosa (RP) and consequent rapid constriction of the visual field in each eye, which is atypical for either of these pathologies.

OBSERVATIONS

A 45-year old male, with a long-standing history of RP, presented with rapid vision loss over 3 months. Examination revealed a severe drop in visual acuity and significant progression of concentric visual field constriction in each eye compared to 3 months prior. MRI revealed a pituitary macroadenoma compressing the optic chiasm. The patient underwent endoscopic trans-sphenoidal resection of the tumor and experienced partial recovery of visual acuity but not visual field.

CONCLUSIONS AND IMPORTANCE

The visual field deficit in this patient was atypical for pituitary adenoma or optic neuropathy. The pattern was most consistent with RP, but the rate of progression was not. In a patient with chiasmal pathology in the setting of pre-existing retinopathy, visual field progression may not be limited exclusively to the bitemporal regions. Rapid constriction of the visual field in a patient with RP should prompt a work-up for alternative etiologies which includes neuro-imaging.

Advancing Clinical Trials for Inherited Retinal Diseases: Recommendations from the Second Monaciano Symposium

Major advances in the study of inherited retinal diseases (IRDs) have placed efforts to develop treatments for these blinding conditions at the forefront of the emerging field of precision medicine. As a result, the growth of clinical trials for IRDs has increased rapidly over the past decade and is expected to further accelerate as more therapeutic possibilities emerge and qualified participants are identified. Although guided by established principles, these specialized trials, requiring analysis of novel outcome measures and endpoints in small patient populations, present multiple challenges relative to study design and ethical considerations. This position paper reviews recent accomplishments and existing challenges in clinical trials for IRDs and presents a set of recommendations aimed at rapidly advancing future progress. The goal is to stimulate discussions among researchers, funding agencies, industry, and policy makers that will further the design, conduct, and analysis of clinical trials needed to accelerate the approval of effective treatments for IRDs, while promoting advocacy and ensuring patient safety.

Autoimmune retinopathy associated with monoclonal gammopathy of undetermined significance: a case report

Background

Monoclonal gammopathy of undetermined significance (MGUS) is a plasma cell dyscrasia and precursor to multiple myeloma. It has known ocular manifestations, but has not previously been shown to have an association with autoimmune retinopathy.

Case presentation

A 57 year-old female presented with 1 year of progressive, bilateral, peripheral vision loss, photopsias, and nyctalopia. Her fundus examination and extensive ancillary testing were concerning for hereditary versus autoimmune retinopathy. The patient was found to have anti-retinal antibodies against carbonic anhydrase II and enolase proteins with a negative genetic retinal dystrophy panel. Malignancy work-up was negative, but the patient was diagnosed with MGUS, a premalignant condition. The patient was treated with immunosuppressive therapies, with rituximab demonstrating the most robust therapeutic response with respect to patient symptoms and ophthalmic testing.

Conclusions

MGUS should be considered as a potential etiology of autoimmune retinopathy in patients without other autoimmune or malignant disease processes. Immunosuppressive therapy may be helpful in limiting disease progression, with rituximab showing efficacy in retinopathy refractory to other agents.

X-Chromosome Inactivation Is a Biomarker of Clinical Severity in Female Carriers of RPGR-Associated X-Linked Retinitis Pigmentosa

PURPOSE

X-linked retinitis pigmentosa can manifest in female carriers with widely variable severity, whereas others remain unaffected. The contribution of X-chromosome inactivation (XCI) to phenotypic variation has been postulated but not demonstrated. Furthermore, the impact of genotype and genetic modifiers has been demonstrated in affected males but has not been well established in female carriers. The purpose of this study was to describe the scope of clinical phenotype in female carriers with mutations in RPGR and quantify the contribution of genotype, genetic modifiers, and XCI to phenotypic severity.

DESIGN

Cohort study.

PARTICIPANTS

Seventy-seven female carriers with RPGR mutations from 41 pedigrees.

METHODS

Coding single nucleotide polymorphisms were sequenced in candidate genetic modifier genes encoding known RPGR-interacting proteins. X-chromosome inactivation ratios were determined in genomic DNA isolated from blood (n = 42) and saliva (n = 20) using methylation status of X-linked polymorphic repeats. These genetic data were compared with disease severity based on quantitative clinical parameters.

MAIN OUTCOME MEASURES

Visual acuity, Humphrey visual field (HVF) results, full-field electroretinography results, and dark adaptation.

RESULTS

Most individuals at all ages were mildly affected or unaffected, whereas those who progressed to moderate or severe vision loss were older than 30 years. RPGR genotype was not associated with clinical severity. The D1264N variant in RPGRIP1L was associated with more severe disease. Skewed XCI toward inactivation of the normal RPGR allele was associated with more severe disease. The XCI ratio in both blood and saliva was a predictor of visual function as measured by HVF diameter, rod amplitude, flicker amplitude, and flicker implicit time. For carriers with extreme XCI skewing of 80:20 or more, 57% were affected severely compared with 8% for those with XCI of less than 80:20 (P = 0.002).

CONCLUSIONS

Female carriers with mutations in RPGR demonstrate widely variable clinical severity. X-chromosome inactivation ratios correlate with clinical severity and may serve as a predictor of clinically significant disease. Because RPGR gene therapy trials are underway, a future imperative exists to determine which carriers require intervention and when to intervene. X-chromosome inactivation analysis may be useful for identifying candidates for early intervention.

Comparison of Fundus-Guided Microperimetry and Multifocal Electroretinography for Evaluating Hydroxychloroquine Maculopathy

Purpose

To compare retinal function by using fundus-guided microperimetry (MP) and multifocal electroretinography (mfERG) for detecting hydroxychloroquine (HCQ) maculopathy.

Methods

Forty-six eyes of 25 patients referred to our clinical practice for HCQ maculopathy assessment and 3 groups of normal control subjects were evaluated by mfERG and MP. Macular structure was assessed using spectral-domain optical coherence tomography (SD-OCT). Ring ratios from the three innermost mERG rings were compared with average sensitivity of each MP ring at approximately equivalent distances from the fovea. HCQ toxicity was defined as an mfERG ring ratio or mean MP ring sensitivity >2 standard deviations below the normal mean. The sensitivity and specificity of MP to detect HCQ toxicity relative to mfERG were evaluated.

Results

MP rings MR2 and MR3 were positively correlated with corresponding mfERG ring ratios (r = 0.52, P = 0.002 and r = 0.56, P < 0.001 respectively). Ring 2 and ring 3 measures of MP and mfERG were significantly worse in HCQ eyes than controls (P < 0.001). The sensitivity of MP to detect toxicity for MR1 through MR3 ranged from 33% to 88%, whereas specificity ranged from 72% to 85%. Through rings 1 to 3, the frequency of abnormal function ranged from 20% to 48% for MP, 11% to 35% for mfERG, and 41% to 45% for SD-OCT.

Conclusions

The frequency of detection of HCQ toxicity with MP was greater than with mfERG. MP showed an overall good sensitivity and moderate specificity in detecting HCQ-induced functional deficits.

Translational Relevance

Results from this study may allow clinicians to improve screening accuracy for HCQ toxicity by using the alternative modality of MP.

Development of a Gene Therapy Vector for RDH12-Associated Retinal Dystrophy

Early-onset severe retinal dystrophy (EOSRD) is a genetically heterogeneous group of diseases resulting in serious visual disability in children. A significant number of EOSRD cases, often diagnosed as Leber congenital amaurosis (LCA13), are associated with mutations in the gene encoding retinol dehydrogenase 12 (RDH12). RDH12 is a member of the enzyme family of short-chain dehydrogenases/reductases. In the retina, RDH12 plays a critical role in reducing toxic retinaldehydes generated by visual cycle activity that is required for the light response of the photoreceptor cells. Individuals with RDH12 deficiency exhibit widespread retinal degeneration impacting both rods and cones. Although Rdh12-deficient (Rdh12^-/-) mice do not exhibit retinal degeneration, functional deficits relevant to visual cycle function can be demonstrated. In the present study, we describe the development and preclinical testing of a recombinant adeno-associated viral (rAAV) vector that has the potential for use in treating EOSRD due to RDH12 mutations. Wild-type and Rdh12^-/- mice that received a subretinal injection of rAAV2/5 carrying a human RDH12 cDNA driven by a human rhodopsin-kinase promoter exhibited transgene expression that was stable, correctly localized, and did not cause retinal toxicity. In addition, administration of the vector reconstituted retinal reductase activity in the retinas of Rdh12^-/- mice and decreased susceptibility to light damage associated with Rdh12 deficiency, thus demonstrating potential therapeutic efficacy in an animal model that does not exhibit a retinal degeneration phenotype. These findings support further efforts to develop gene replacement therapy for individuals with RDH12 mutations.

Detailed clinical characterisation, unique features and natural history of autosomal recessive RDH12-associated retinal degeneration

BACKGROUND

Defects in retinol dehydrogenase 12 (RDH12) account for 3.4%-10.5 % of Leber congenital amaurosis and early-onset severe retinal dystrophy (EOSRD) and are a potential target for gene therapy. Clinical trials in inherited retinal diseases have unique challenges, and natural history studies are critical to successful trial design. The purpose of this study was to characterise the natural history of RDH12-associated retinal degeneration.

METHODS

A retrospective chart review was performed in individuals with retinal degeneration and two likely disease-causing variants in RDH12.

RESULTS

57 subjects were enrolled from nine countries. 33 subjects had clinical records available from childhood. The data revealed an EOSRD, with average age of onset of 4.1 years. Macular atrophy was a universal clinical finding in all subjects, as young as 2 years of age. Scotopic and photopic electroretinography (ERG) responses were markedly reduced in all subjects, and a non-recordable ERG was documented as young as 1 year of age. Assessment of visual acuity, visual field and optical coherence tomography revealed severe loss of function and structure in the majority of subjects after the age of 10 years. Widefield imaging in 23 subjects revealed a unique, variegated watercolour-like pattern of atrophy in 13 subjects and sparing of the peripapillary area in 18 subjects.

CONCLUSIONS

This study includes the largest collection of phenotypic data from children with RDH12-associated EOSRD and provides a comprehensive description of the timeline of vision loss in this severe, early-onset condition. These findings will help identify patients with RDH12-associated retinal degeneration and will inform future design of therapeutic trials.

Macular hyperpigmentary changes in ABCA4-Stargardt disease

Background

Stargardt disease (STGD) and age-related macular degeneration (AMD) share clinical and pathophysiological features. In AMD, macular hyperpigmentary changes are associated to a worse prognosis. The purpose of this study was to characterize macular hyperpigmentary changes in patients with STGD and associate them with the severity of phenotype.

Materials and methods

This retrospective cross-sectional study included 141 patients with STGD. Hyperpigmentary changes were evaluated on color fundus photography and spectral-domain optical coherence tomography. Severity of phenotype was assessed by full-field electroretinogram (ffERG) and fundus autofluorescence (FAF) patterns, and visual acuity (VA).

Results

Thirty patients (21.7%) showed macular hyperpigmentary changes in four distinct patterns. Out of seventeen patients who had follow-up images, eleven patients demonstrated increases of the hyperpigmented lesions, and progression of the underlying RPE atrophy overtime. VA remained stable. Of 28 patients who had ffERG, 17 patients presented with reduction of photopic and scotopic responses, while 8 presented with reduction of photopic responses only, and 3 presented with preserved photopic and scotopic responses. Of 25 patients who had FAF available, 12 presented with widespread disease extending anteriorly to the vascular arcades, while eight presented with widespread disease, extending beyond the vascular arcades, and 5 presented with disease confined to the foveal area.

Conclusion

In this study, we demonstrated that patients with STGD with macular hyperpigmented lesions had a severe phenotype. Overtime, hyperpigmented lesions increased in size, spread across the retina, and migrated to different retinal layers. Macular hyperpigmentation may be a marker of advanced stage of the disease.

Contrast sensitivity deficits in patients with mutation-proven inherited retinal degenerations

BACKGROUND

Patients with retinal diseases frequently complain of poor visual function even when visual acuity is relatively unaffected. This clinical finding has been attributed to deficits in contrast sensitivity (CS). The purpose of our study was to evaluate the CS in patients with clinical and genetic diagnosis of inherited retinal degeneration (IRD) and relatively preserved visual acuity.

METHODS

Seventeen patients (30 eyes) with IRD and visual acuity of 20/40 or better, and 18 controls (18 eyes) without any ocular condition underwent slit lamp examination, visual acuity testing via standard Snellen chart testing, CS testing via the Quick Contrast Sensitivity Function (QCSF), and Spectral Domain Optical Coherence Tomography (SD-OCT). CS were measured at 1.0, 1.5, 3.0, 6.0, 12.0, and 18.0 cycles per degree (cpd). T tests with general estimated equations were used to compare CS between groups. Wald chi square followed by pairwise comparisons was used to compare CS between multiple groups.

RESULTS

We included 12 patients with rod-cone dystrophy (RCD), 3 patients with Stargardt disease (STGD) and 2 patients with Best disease. Patients with IRD had significantly worse CS than controls (p < 0.001) in all spatial frequencies. Patients with STGD had more marked deficits in CS than patients with Best disease (p < 0.001) and RCD (p < 0.001) despite having similar visual acuities.

CONCLUSION

Patients with IRD, especially patients with STGD with relatively preserved visual acuity have marked deficits in CS when measured across a range of spatial frequencies. We recommend that clinical trials for STGD incorporate CS measured over a range of spatial frequencies as a secondary clinical endpoint for monitoring visual function. CS may provide an explanation for complaints of visual dysfunction when visual acuity is not significantly altered.

Inhibiting autophagy reduces retinal degeneration caused by protein misfolding

Mutations in the genes necessary for the structure and function of vertebrate photoreceptor cells are associated with multiple forms of inherited retinal degeneration. Mutations in the gene encoding RHO (rhodopsin) are a common cause of autosomal dominant retinitis pigmentosa (adRP), with the Pro23His variant of RHO resulting in a misfolded protein that activates endoplasmic reticulum stress and the unfolded protein response. Stimulating macroautophagy/autophagy has been proposed as a strategy for clearing misfolded RHO and reducing photoreceptor death. We found that retinas from mice heterozygous for the gene encoding the RHOP23H variant (hereafter called P23H) exhibited elevated levels of autophagy flux, and that pharmacological stimulation of autophagy accelerated retinal degeneration. In contrast, reducing autophagy flux pharmacologically or by rod-specific deletion of the autophagy-activating gene Atg5, improved photoreceptor structure and function. Furthermore, proteasome levels and activity were reduced in the P23H retina, and increased when Atg5 was deleted. Our findings suggest that autophagy contributes to photoreceptor cell death in P23H mice, and that decreasing autophagy shifts the degradation of misfolded RHO protein to the proteasome and is protective. These observations suggest that modulating the flux of misfolded proteins from autophagy to the proteasome may represent an important therapeutic strategy for reducing proteotoxicity in adRP and other diseases caused by protein folding defects.

IFT88 mutations identified in individuals with non-syndromic recessive retinal degeneration result in abnormal ciliogenesis

Whole genome sequencing (WGS) was performed to identify the variants responsible for inherited retinal degeneration (IRD) in a Caucasian family. Segregation analysis of selected rare variants with pathogenic potential identified a set of compound heterozygous changes p.Arg266*:c.796C>T and p.Ala568Thr:c.1702G>A in the intraflagellar transport protein-88 (IFT88) gene segregating with IRD. Expression of IFT88 with the p.Arg266* and p.Ala568Thr mutations in mIMDC3 cells by transient transfection and in HeLa cells by introducing the mutations using CRISPR-cas9 system suggested that both mutations result in the formation of abnormal ciliary structures. The introduction of the IFT88 p.Arg266* variant in the homozygous state in HeLa cells by CRISPR-Cas9 genome-editing revealed that the mutant transcript undergoes nonsense-mediated decay leading to a significant depletion of IFT88 transcript. Additionally, abnormal ciliogenesis was observed in these cells. These observations suggest that the rare and unique combination of IFT88 alleles observed in this study provide insight into the physiological role of IFT88 in humans and the likely mechanism underlying retinal pathology in the pedigree with IRD.

A specific phosphorylation regulates the protective role of αA-crystallin in diabetes

Neurodegeneration is a central aspect of the early stages of diabetic retinopathy, the primary ocular complication associated with diabetes. While progress has been made to improve the vascular perturbations associated with diabetic retinopathy, there are still no treatment options to counteract the neuroretinal degeneration associated with diabetes. Our previous work suggested that the molecular chaperones α-crystallins could be involved in the pathophysiology of diabetic retinopathy; however, the role and regulation of α-crystallins remained unknown. In the present study, we demonstrated the neuroprotective role of αA-crystallin during diabetes and its regulation by its phosphorylation on residue 148. We further characterized the dual role of αA-crystallin in neurons and glia, its essential role for neuronal survival, and its direct dependence on phosphorylation on this residue. These findings support further evaluation of αA-crystallin as a treatment option to promote neuron survival in diabetic retinopathy and neurodegenerative diseases in general.

Double hyperautofluorescent ring on fundus autofluorescence in ABCA4

We report an unusual phenotype in a child with a clinical diagnosis of recessive Stargardt disease (STGD1) and two pathogenic variants in the ABCA4 gene. Typically, the diagnosis of early-onset STGD1 is challenging because children may present with a variety of fundus changes and a variable rate of progression. At the time of his initial visit, the 6-year-old boy presented with 20/200 OD (right eye) and 20/150 OS (left eye), symmetrical mild foveal atrophy without flecks on fundus exam, and foveal hypoautofluorescence surrounded by a homogeneous hyperautofluorescent background on wide-field fundus autofluorescence. Over 4 years of follow-up, the retinal atrophy continued to progress, resulting in two well-defined and concentric hyperautofluorescent rings: one ring located at the posterior pole and the other located around the peripapillary region. Visual acuity also deteriorated to counting fingers at 4ft OD and 20/500 OS. To the best of our knowledge, this phenotype has not been previously described with the ABCA4 gene.

Reliability of kinetic visual field testing in children with mutation-proven retinal dystrophies: Implications for therapeutic clinical trials

PURPOSE

Kinetic visual field testing is used to monitor disease course in retinal dystrophy clinical care and treatment response in treatment trials, which are increasingly recruiting children. This study investigates Goldmann visual field (GVF) changes in young children with mutation-proven retinal dystrophies as they age and with progression of the retinal degeneration.

METHODS

Retrospective review of children ≤ 17 years old with a mutation-proven retinal dystrophy. Objective clinical disease activity was assessed by a retinal degeneration specialist masked to GVF results. Digital quantification of GVF area was performed.

RESULTS

Twenty-nine children (58 eyes), ages 5-16, were identified. GVF area increased with age despite progression in 20 children and clinical stability in nine children. Mean ± standard error increase in GVF area/year was 333 ± 130 mm² (I4e, p = 0.012), 720 ± 155 mm² (III4e, p < 0.001), and 759 ± 167 mm² (IV4e, p < 0.001), with greater increases at earlier ages. Repeatability coefficients were 7381 mm² (I4e), 9379 mm² (III4e), and 10346 mm² (IV4e), indicating a large variability. At 2.5 years after the baseline GVF the area increased ≥ 20%, the criterion for positive treatment outcome defined in recent published therapeutic trials, in 38% (I4e), 34% (III4e), and 33% (IV4e) of eyes.

CONCLUSION

In a substantial proportion of children with mutation-proven retinal dystrophies, there is a significant increase in GVF area with age, particularly those < 12 years, despite progression or stability of disease. These findings suggest that change in GVF area in children with retinal dystrophies can be an unreliable measure of response to treatment and on which to base appropriate counseling about visual impairment.

Autophagy-mediated catabolism of visual transduction proteins prevents retinal degeneration

Autophagy is a lysosomal degradation pathway critical to preventing the accumulation of cytotoxic proteins. Deletion of the essential autophagy gene Atg5 from the rod photoreceptors of the retina (atg5^Δrod mouse) results in the accumulation of the phototransduction protein transducin and the degeneration of these neurons. The purpose of this study is to test the hypothesis that autophagic degradation of visual transduction proteins prevents retinal degeneration. Targeted deletion of both Gnat1 (a gene encoding the α subunit of the heterotrimeric G-protein transducin) and Atg5 in the rod photoreceptors resulted in a significantly decreased rate of rod cell degeneration as compared to the atg5^Δrod mouse retina, and considerable preservation of photoreceptors. Supporting this we used a novel technique to immunoprecipitate green fluorescent protein (GFP)-tagged autophagosomes from the retinas of the GFP-LC3 mice and demonstrated that the visual transduction proteins transducin and ARR/arrestin are associated with autophagosome-specific proteins. Altogether, this study shows that degradation of phototransduction proteins by autophagy is necessary to prevent retinal degeneration. In addition, we demonstrate a simple and easily reproducible immunoisolation technique for enrichment of autophagosomes from the GFP-LC3 mouse retina, providing a novel application to the study of autophagosome contents across different organs and specific cell types in vivo.

Advancing therapeutic strategies for inherited retinal degeneration: recommendations from the Monaciano Symposium

Although rare in the general population, retinal dystrophies occupy a central position in current efforts to develop innovative therapies for blinding diseases. This status derives, in part, from the unique biology, accessibility, and function of the retina, as well as from the synergy between molecular discoveries and transformative advances in functional assessment and retinal imaging. The combination of these factors has fueled remarkable progress in the field, while at the same time creating complex challenges for organizing collective efforts aimed at advancing translational research. The present position paper outlines recent progress in gene therapy and cell therapy for this group of disorders, and presents a set of recommendations for addressing the challenges remaining for the coming decade. It is hoped that the formulation of these recommendations will stimulate discussions among researchers, funding agencies, industry, and policy makers that will accelerate the development of safe and effective treatments for retinal dystrophies and related diseases.

Loss of Raf-1 kinase inhibitory protein delays early-onset severe retinal ciliopathy in Cep290rd16 mouse

PURPOSE

Mutations in the cilia-centrosomal protein of centrosomal protein of 290 kDa (CEP290) result in severe ciliopathies, including autosomal recessive early onset childhood blindness disorder Leber congenital amaurosis (LCA). The Cep290(rd16) (retinal degeneration 16) mouse model of CEP290-LCA exhibits accumulation of CEP290-interacting protein Raf-1 kinase inhibitory protein (RKIP) prior to onset of retinal degeneration (by postnatal day P14). We hypothesized that reducing RKIP levels in the Cep290(rd16) mouse will delay or improve retinal phenotype.

METHODS

We generated double mutant mice by combining the Cep290(rd16) and Rkip(ko) alleles (Cep290(rd16):Rkip(+/ko) and Cep290(rd16):Rkip(ko/ko)). Retinal function was assessed by ERG and retinal morphology and protein trafficking were assessed by histology, transmission electron microscopy (TEM), and immunofluorescence analysis. Cell death was examined by apoptosis.

RESULTS

Prior to testing our hypothesis, we examined ERG and retinal morphology of Rkip(ko/ko) mice and did not find any detectable differences compared with wild-type mice. The Cep290(rd16):Rkip(+/ko) mice exhibited similar retinopathy as Cep290(rd16); however, Cep290(rd16): Rkip(ko/ko) double knockout mice demonstrated a substantial improvement (>9-fold) in photoreceptor function and structure at P18 as of Cep290(rd16) mice. We consistently detected transient preservation of photoreceptors at P18 and polarized trafficking of opsins to sensory cilia in the double mutant mice; however, retinal degeneration ensued by P30.

CONCLUSIONS

Our studies implicate CEP290-RKIP pathway in CEP290-retinal degeneration and suggest that targeting RKIP levels can delay photoreceptor degeneration, assisting in extending the time-window for treating such rapidly progressing blindness disorder.

Acute panretinal structural and functional abnormalities after intravitreous ocriplasmin injection

IMPORTANCE Ocriplasmin cleaves fibronectin and laminin, components of the vitreous gel, and is used as a pharmacologic treatment for vitreomacular traction. Laminin is also found throughout multiple retinal layers. Ocriplasmin injection may lead to acute panretinal dysfunction in some eyes, but the mechanism of this toxic reaction has not been described. OBSERVATIONS We evaluated a 63-year-old woman demonstrating acute panretinal dysfunction after intravitreous ocriplasmin injection for a small macular hole with vitreomacular adhesion. Findings included visual acuity loss, visual field constriction, pupillary abnormalities, attenuated retinal arteries, loss of outer retinal signals on spectral-domain optical coherence tomography, and severely reduced electroretinography responses. B-waves were reduced more than A-waves were, suggesting postreceptoral dysfunction and decreased photoreceptor activity. CONCLUSIONS AND RELEVANCE Retinal dysfunction associated with intravitreous ocriplasmin injection is not limited to the macular region and seems to involve the entire retina. Enzymatic cleavage of intraretinal laminin is a biologically plausible mechanism for acute ocriplasmin retinal toxic effects.

Diagnostic fundus autofluorescence patterns in achromatopsia

PURPOSE

To describe the unique diagnostic fundus autofluorescence (FAF) patterns in patients with achromatopsia and the associated findings on optical coherence tomography (OCT).

DESIGN

Observational case series.

METHODS

We evaluated 10 patients with achromatopsia by means of best-corrected visual acuity (BCVA), ophthalmoscopy, Goldmann visual field, full-field electroretinography (ffERG), OCT, and FAF photography. FAF patterns were compared with patient age and foveal changes on OCT.

RESULTS

Patients fell into two dichotomous age groups at the time of evaluation: six patients ranged from 11 to 23 years of age, and 3 patients ranged from 52 to 63 years of age. All patients had severely reduced photopic ffERG responses, including those exhibiting preserved foveal structure on OCT. The younger patients had absent to mild foveal atrophy on OCT, and four of the six demonstrated foveal and parafoveal hyperfluorescence on FAF. In addition, a 7-month-old child with compound heterozygous mutations in CNGA3 demonstrated similar foveal hyperfluorescence. The older patients demonstrated advanced foveal atrophy and punched-out foveal hypofluorescence with discrete borders on FAF imaging corresponding to the area of outer retinal cavitation on OCT.

CONCLUSIONS

Foveal hyperfluorescence is an early sign of achromatopsia that can aid in clinical diagnosis. In our cohort, patients with achromatopsia demonstrated age-dependent changes in FAF, which are likely to be progressive and to correlate with foveal atrophy and cavitation on OCT. This finding may be useful in charting the natural course of the disease and in defining a therapeutic window for treatment.

Multifocal visual evoked potentials for early glaucoma detection

BACKGROUND AND OBJECTIVE

To compare multifocal visual evoked potentials (mfVEP) with other detection methods in early open-angle glaucoma.

PATIENTS AND METHODS

Ten patients with suspected glaucoma and 5 with early open-angle glaucoma underwent mfVEP, standard automated perimetry (SAP), short-wave automated perimetry, frequency-doubling technology perimetry, and nerve fiber layer optical coherence tomography. Nineteen healthy control subjects underwent mfVEP and SAP for comparison. Comparisons between groups involving continuous variables were made using independent t tests; for categorical variables, Fisher's exact test was used.

RESULTS

Monocular mfVEP cluster defects were associated with an increased SAP pattern standard deviation (P = .0195). Visual fields that showed interocular mfVEP cluster defects were more likely to also show superior quadrant nerve fiber layer thinning by OCT (P = .0152).

CONCLUSION

Multifocal visual evoked potential cluster defects are associated with a functional and an anatomic measure that both relate to glaucomatous optic neuropathy.

Rd9 is a naturally occurring mouse model of a common form of retinitis pigmentosa caused by mutations in RPGR-ORF15

Animal models of human disease are an invaluable component of studies aimed at understanding disease pathogenesis and therapeutic possibilities. Mutations in the gene encoding retinitis pigmentosa GTPase regulator (RPGR) are the most common cause of X-linked retinitis pigmentosa (XLRP) and are estimated to cause 20% of all retinal dystrophy cases. A majority of RPGR mutations are present in ORF15, the purine-rich terminal exon of the predominant splice-variant expressed in retina. Here we describe the genetic and phenotypic characterization of the retinal degeneration 9 (Rd9) strain of mice, a naturally occurring animal model of XLRP. Rd9 mice were found to carry a 32-base-pair duplication within ORF15 that causes a shift in the reading frame that introduces a premature-stop codon. Rpgr ORF15 transcripts, but not protein, were detected in retinas from Rd9/Y male mice that exhibited retinal pathology, including pigment loss and slowly progressing decrease in outer nuclear layer thickness. The levels of rhodopsin and transducin in rod outer segments were also decreased, and M-cone opsin appeared mislocalized within cone photoreceptors. In addition, electroretinogram (ERG) a- and b-wave amplitudes of both Rd9/Y male and Rd9/Rd9 female mice showed moderate gradual reduction that continued to 24 months of age. The presence of multiple retinal features that correlate with findings in individuals with XLRP identifies Rd9 as a valuable model for use in gaining insight into ORF15-associated disease progression and pathogenesis, as well as accelerating the development and testing of therapeutic strategies for this common form of retinal dystrophy.

Excess cones in the retinal degeneration rd7 mouse, caused by the loss of function of orphan nuclear receptor Nr2e3, originate from early-born photoreceptor precursors

The orphan nuclear receptor NR2E3 is a direct transcriptional target of NRL, the key basic motif leucine zipper transcription factor that dictates rod versus cone photoreceptor cell fate in the mammalian retina. The lack of NR2E3 function in humans and in retinal degeneration rd7 mutant mouse leads to increased S-cones accompanied by rod degeneration, whereas ectopic expression of Nr2e3 in the cone-only Nrl(-/-) retina generates rod-like cells that do not exhibit any visual function. Using GFP to tag the newborn rods and by 5-bromo-2'-deoxyuridine birthdating, we demonstrate that early-born post-mitotic photoreceptor precursors in the rd7 retina express cone-specific genes. Transgenic mouse studies in the rd7 background show that Nr2e3 when expressed under the control of Crx promoter can restore rod photoreceptor function and suppress cone gene expression. Furthermore, Nr2e3 expression in photoreceptor precursors committed to be rods (driven by the Nrl promoter) could completely rescue the retinal phenotype of the rd7 mice. We conclude that excess of S-cones in the rd7 retina originate from photoreceptor precursors with a 'default' fate and not from proliferation of cones and that Nr2e3 is required to suppress the expression of S-cone genes during normal rod differentiation. These studies further support the 'transcriptional dominance' model of photoreceptor cell fate determination and provide insights into the pathogenesis of retinal disease phenotypes caused by NR2E3 mutations.

A CTRP5 gene S163R mutation knock-in mouse model for late-onset retinal degeneration

Late-onset retinal macular degeneration (L-ORD) is an autosomal dominant inherited disorder caused by a single missense mutation (S163R) in the CTRP5/C1QTNF5 protein. Early phenotypic features of L-ORD include: dark adaptation abnormalities, nyctalopia, and drusen deposits in the peripheral macular region. Apart from posterior segment abnormalities, these patients also develop abnormally long anterior lens zonules. In the sixth decade of life the rod and cone function declines, accompanied by electroretinogram (ERG) abnormalities. Some patients also develop choroidal neovascularization and glaucoma. In order to understand the disease pathology and mechanisms involved in retinal dystrophy, we generated a knock-in (Ctrp5(+/-)) mouse model carrying the disease-associated mutation in the mouse Ctrp5/C1QTNF5 gene. These mice develop slower rod-b wave recovery consistent with early dark adaptation abnormalities, accumulation of hyperautofluorescence spots, retinal pigment epithelium abnormalities, drusen, Bruch's membrane abnormalities, loss of photoreceptors, and retinal vascular leakage. The Ctrp5(+/-) mice, which have most of the pathological features of age-related macular degeneration, are unique and may serve as a valuable model both to understand the molecular pathology of late-onset retinal degeneration and to evaluate therapies.

Distinct signature of altered homeostasis in aging rod photoreceptors: implications for retinal diseases

Background

Advanced age contributes to clinical manifestations of many retinopathies and represents a major risk factor for age-related macular degeneration, a leading cause of visual impairment and blindness in the elderly. Rod photoreceptors are especially vulnerable to genetic defects and changes in microenvironment, and are among the first neurons to die in normal aging and in many retinal degenerative diseases. The molecular mechanisms underlying rod photoreceptor vulnerability and potential biomarkers of the aging process in this highly specialized cell type are unknown.

Methodology/Principal Findings

To discover aging-associated adaptations that may influence rod function, we have generated gene expression profiles of purified rod photoreceptors from mouse retina at young adult to early stages of aging (1.5, 5, and 12 month old mice). We identified 375 genes that showed differential expression in rods from 5 and 12 month old mouse retina compared to that of 1.5 month old retina. Quantitative RT-PCR experiments validated expression change for a majority of the 25 genes that were examined. Macroanalysis of differentially expressed genes using gene class testing and protein interaction networks revealed overrepresentation of cellular pathways that are potentially photoreceptor-specific (angiogenesis and lipid/retinoid metabolism), in addition to age-related pathways previously described in several tissue types (oxidative phosphorylation, stress and immune response).

Conclusions/Significance

Our study suggests a progressive shift in cellular homeostasis that may underlie aging-associated functional decline in rod photoreceptors and contribute to a more permissive state for pathological processes involved in retinal diseases.

Two mouse models for recoverin-associated autoimmune retinopathy

PURPOSE

Recoverin has been demonstrated to be one of the main causative antigenic retinal proteins common in many cases of autoimmune retinopathy (AIR). Strategies for producing two different AIR mouse models associated with anti-recoverin antibodies were tested.

METHODS

(1) Six-week-old female B6.MRL-Fal(lpr)/J mice (LPR) mice were immunized with recombinant recoverin three times at 2-4 week intervals. (2) Five-month-old Balb/cJ mice were injected with hybridoma cells designed to produce recoverin monoclonal antibodies. Anti-recoverin antibodies were analyzed by immunoblot and enzyme-linked immunosorbent assay (ELISA). Electroretinograms (ERG), histopathologic examination, and flow cytometric analysis were assessed.

RESULTS

High anti-recoverin antibody levels were achieved in both models, accompanied by significantly reduced scotopic and photopic responses on the ERGs. Retinal histology showed swollen cell bodies in the inner nuclear layer in recoverin-immunized LPR mice, while photoreceptor and outer nuclear layer swelling was observed in recoverin hybridoma cells injected into balb/cJ mice. Glial fibrillary acidic protein (GFAP) staining detected a marked increase of Müller cells and astrocyte reactive gliosis in both mouse models. Rhodopsin and S-opsin staining was similar to controls, while decreased numbers of bipolar cells were observed in both models. Complement component C1q and C3 deposits increased upon immunohistopathologic retinal staining in both models, while increased numbers of CD4+ and CD68+ cells from retinas were found upon flow cytometric analysis.

CONCLUSIONS

These two models had similar pathology in the retina, indicating the retinal antigens to recoverin antibody set off pathologic events that include leukocyte invasion, complement deposition, reactive gliosis in the retina, and selective retinal degeneration of inner nuclear layer neurons. These two AIR mouse models will allow for detailed pathologic investigation and testing of protein antigens associated with human AIR and can be used to test treatments. It is important to note that, since most AIR patients have multiple anti-retinal antibodies, it will be possible to study which antibodies are pathologic and which have no retinal pathologic effects. These models can also serve as an important research resource for studying the pathophysiology of specific retinal proteins by creating autoantibodies, which potentially will give a better understanding of retinal protein interactions.

Elovl4 5-bp deletion knock-in mouse model for Stargardt-like macular degeneration demonstrates accumulation of ELOVL4 and lipofuscin

The mechanism underlying photoreceptor degeneration in autosomal dominant Stargardt-like macular degeneration (STGD3) due to mutations in the elongation of very long chain fatty acids-4 (ELOVL4) gene is not fully understood. To evaluate the pathological events associated with STGD3, we used a mouse model that mimics the human STGD3 phenotype and studied the progression of retinal degeneration. Morphological changes in the retina of Elovl4 5-bp deletion knock-in mice (E_mut(+/-)) were evaluated at 22 months of age. The localization of ELOVL4, and the expression pattern of inner retinal tissue marker proteins, and ubiquitin were determined by immunofluorescence labeling of retinal sections. Levels of the retinal pigment epithelium (RPE) lipofuscin fluorophores were measured by quantitative HPLC. Morphological evaluation of the retina revealed an accumulation of RPE debris in the subretinal space. A significant increase in the amount of ELOVL4 was observed in the outer plexiform layer in E_mut(+/-) mice compared to controls. Apart from the accumulation of ELOVL4, E_mut(+/-) mice also exhibited high expression of ubiquitin in the retina. Analysis of lipofuscin fluorophores in the RPE showed a significant elevation of A2E and compounds of the all-trans-retinal dimer series in retinas from four and ten month old E_mut(+/-) mice compared to wild-type littermates. These observations suggest that abnormal accumulation of ELOVL4 protein and lipofuscin may lead to photoreceptor degeneration in E_mut(+/-) mice.

Management of autoimmune retinopathies with immunosuppression

OBJECTIVE

To report the results of treating autoimmune retinopathy (AIR) with immunosuppression therapy.

METHODS

Retrospective review of 30 consecutive patients with AIR followed for 3 to 89 months (median, 17 months) who were treated with immunosuppression (systemic or local). Subgroups were cancer-associated retinopathy (CAR), nonparaneoplastic AIR (npAIR), and npAIR with cystoid macular edema (npAIR/CME). Outcome measures were improvement of Snellen visual acuity by at least 2 lines, expansion of the visual field area by more than 25%, and resolution of CME.

RESULTS

Overall, 21 of 30 patients (70%) showed improvement. All 6 CAR patients, 7 of 13 (54%) with npAIR, and 8 of 11 (73%) with npAIR/CME showed improvement. Five of 21 patients (24%) had improvement in visual acuity, 15 of 21 (71%) had expansion of visual field area, and 6 of 11 (55%) had resolution of CME. Twenty-six of 30 patients exhibited diffuse retinal atrophy without pigment deposits. An autoimmune family history was common in all the groups: npAIR, 69% (9 of 13); npAIR/CME, 64% (7 of 11); and CAR, 50% (3 of 6).

CONCLUSIONS

Long-term treatment with immunosuppression resulted in clinical improvement in all subgroups of AIR. The most responsive subgroup was CAR; the least was npAIR. These results challenge the commonly held belief that AIR is untreatable.

Age-related retinal degeneration (arrd2) in a novel mouse model due to a nonsense mutation in the Mdm1 gene

We observed that a naturally occurring mouse strain developed age-related retinal degeneration (arrd2). These mice had normal fundi, electroretinograms (ERGs) and retinal histology at 6 months of age; vessel attenuation, RPE atrophy and pigmentary abnormalities at 14 months, which progressed to complete loss of photoreceptors and extinguished ERG by 22 months. Genetic analysis revealed that the retinal degeneration in arrd2 segregates in an autosomal recessive manner and the disease gene localizes to mouse chromosome 10. A positional candidate cloning approach detected a nonsense mutation in the mouse double minute-1 gene (Mdm1), which results in the truncation of the putative protein from 718 amino acids to 398. We have identified a novel transcript of the Mdm1 gene, which is the predominant transcript in the retina. The Mdm1 transcript is localized to the nuclear layers of neural retina. Expression of Mdm1 in the retina increases steadily from post-natal day 30 to 1 year, and a high level of Mdm1 are subsequently maintained. The Mdm1 transcript was found to be significantly depleted in the retina of arrd2 mice and the transcript was observed to degrade by nonsense-mediated decay. These results indicate that the depletion of the Mdm1 transcript may underlie the mechanism leading to late-onset progressive retinal degeneration in arrd2 mice. Analysis of a cohort of patients with age-related macular degeneration (AMD) wherein the susceptibility locus maps to chromosome 12q, a region bearing the human ortholog to MDM1, did not reveal association between human MDM1 and AMD.

Nrl-knockout mice deficient in Rpe65 fail to synthesize 11-cis retinal and cone outer segments

PURPOSE

To define rod and cone function further in terms of visual cycle mechanism, the retinal phenotype resulting from Rpe65 (retinoid isomerase I) deficiency in Nrl(-)(/)(-) mice having a single class of photoreceptors resembling wild-type cones was characterized and outcomes of retinoid supplementation evaluated.

METHODS

Rpe65(-)(/)(-)/Nrl(-)(/)(-) mice were generated by breeding Rpe65(-)(/)(-) and Nrl(-)(/)(-) strains. Retinal histology, protein expression, retinoid content, and electroretinographic (ERG) responses were evaluated before and after treatment with 11-cis retinal by intraperitoneal injection. Results Retinas of young Rpe65(-)(/-)/Nrl(-)(/-) mice exhibited normal lamination, but lacked intact photoreceptor outer segments at all ages examined. Rpe65, Nrl, and rhodopsin were not detected, and S-opsin and M/L-opsin levels were reduced. Retinyl esters were the only retinoids present. In contrast, Nrl(-)(/)(-) mice exhibited decreased levels of retinaldehydes and retinyl esters, and elevated levels of retinols. ERG responses were elicited from Rpe65(-)(/-)/Nrl(-)(/-) mice only at the two highest intensities over a 4-log-unit range. Significant retinal thinning and outer nuclear layer loss occurred in Rpe65(-)(/-)/Nrl(-)(/-) mice with aging. Administration of exogenous 11-cis retinal did not rescue retinal morphology or markedly improve ERG responses.

CONCLUSIONS

The findings provide clarification of reported cone loss of function in Rpe65(-)(/-)/Nrl(-)(/-) mice, now showing that chromophore absence results in destabilized cone outer segments and rapid retinal degeneration. The data support the view that rod-dominant retinas do not have a cone-specific mechanism for 11-cis retinal synthesis and have potential significance for therapeutic strategies for rescue of cone-rich retinal regions affected by disease in the aging human population.

Primate Retinal Signaling Pathways: Suppressing ON-Pathway Activity in Monkey With Glutamate Analogues Mimics Human CSNB1-NYX Genetic Night Blindness

Retinal on-pathway dysfunction is implicated in human complete-type congenital stationary night blindness (CSNB1), a Mendelian genetic condition that results from mutations in the NYX gene encoding the protein nyctalopin. We probed cone pathway dysfunction in four human genotyped CSNB1 affected males by electroretinogram (ERG) recordings elicited with photopic sinusoidal and rapid-on/off-ramp flicker stimuli that are reputed to elicit on/off-pathway activity selectively. Results were analyzed in relation to ERG abnormalities created in anesthetized non-human primates by intravitreal application of glutamate analogues that selectively suppress retinal on- or off-pathway bipolar cell activity. 2-amino-4-phosphonobutyric acid (APB), which selectively blocks light responses of on-pathway depolarizing bipolar cells, fully recreated the essential ERG abnormalities found for human CSNB1 under the condition that the off-pathway remained active. Both CSNB1-NYX humans and APB-treated monkey retina lacked the normal amplitude dip and the phase deflection that occurs in the fundamental component near 12 Hz for sinusoidal flicker stimuli. The off-pathway suppressing agent, cis-2,3-piperidine-dicarboxylic acid (PDA), gave results in monkey quite discordant to CSNB1 human for sinusoidal stimulation. The results implicated a specific on-pathway signaling deficiency in CSNB1-NYX males with no evidence of off-pathway involvement. Likewise, rapid-on/off ramping stimuli also indicated that the functional deficit was localized to the on pathway. Analysis of non-human primate retinal responses after drug application demonstrated a complexity to on/off-pathway contributions to ramping on/off ERG responses not previously anticipated. These results support the hypothesis that nyctalopin acts principally or exclusively within the on pathway at the level of depolarizing bipolar cells, and thus human CSNB1-NYX subjects provide an opportunity to probe the primate visual system for consequences of on-pathway deficits.

Clinical course and visual function in a family with mutations in the RPE65 gene

OBJECTIVE

To evaluate the phenotype of affected and carrier members of a family with mutations in RPE65 (a retinal pigment epithelium gene).

METHODS

RPE65 mutation screening was performed on DNA from 2 affected brothers, 1 unaffected brother, both parents, and 3 surviving grandparents using cycle sequencing. Ophthalmic examinations included ophthalmoscopic fundus examination; visual function testing; 2-color, static, dark-adapted threshold perimetry; and rod electroretinographic a-wave phototransduction analysis.

RESULTS

The 2 affected brothers carried RPE65 mutations in compound heterozygous form: a maternal Y368H (1156T-->C) missense mutation and a paternal IVS1 + 5g-->a splice-site mutation. Severe visual deficits and an absence of rod and cone electroretinographic responses were diagnosed in both affected boys before the age of 5 years. Visual acuities of about 20/100 during grade school declined to hand movements by the teenage years, and only a rudimentary peripheral temporal visual field remained by the ages of 25 and 29 years. Both parents had normal central visual function, as measured by visual acuity, contrast sensitivity, color vision, and Humphrey 10-2 fields. However, the 50-year-old father showed hundreds of tiny whitish hard drusen in both eyes and had abnormal peripheral function on dark-adapted perimetry, with extended field defects of 15 to 20 dB outside 30 degrees eccentricity. His rod photoreceptor sensitivity and amplitude, calculated by fitting the rod a waves by a model of activation of phototransduction, were normal, but the flicker electroretinographic response was delayed.

CONCLUSIONS

The RPE65 mutations Y368H and IVS1 + 5g-->a present in compound heterozygous form cause severe visual compromise in childhood and progress to nearly total vision loss by the second to third decades of life. The retinal and functional changes in the father carrying a presumed functional null allele suggest that some RPE65 heterozygous carriers may manifest visual symptoms.

Analysis of photoreceptor function and inner retinal activity in juvenile X-linked retinoschisis

Thirteen retinoschisis males with genotyped XLRS1 gene mutations were examined by electroretinogram (ERG) techniques to determine photoreceptor involvement and ON-pathway and OFF-pathway sites of dysfunction. Parameters R(max) and logS determined by fitting the mathematical model of the activation phase of phototransduction to the scotopic and photopic a-wave responses, were not significantly different from normal. However, the XLRS photopic a-wave amplitudes were significantly lower than normal across all intensities, consistent with defective signaling in the OFF pathway. Long flash (150 ms) ON-OFF photopic responses showed reduced b-wave amplitude but normal d-wave amplitude, giving a reduced b/d ratio of <1.32 Hz photopic flicker ERG fundamental frequency responses showed reduced amplitude and delayed phase, consistent with abnormal signaling by both the ON- and OFF-pathway components. These results indicate that the XLRS1 protein appears not to affect photoreceptor function directly for most XLRS males, and that ERG signaling abnormalities occur in both the ON- and OFF-pathway components that originate in the proximal retina.

P23H rhodopsin transgenic rat: correlation of retinal function with histopathology

PURPOSE

To correlate retinal functional changes with structural changes in P23H rhodopsin transgenic rats as a model of autosomal dominant retinitis pigmentosa.

METHODS

P23H heterozygote (lines 1 and 3) and Sprague-Dawley control rats were studied at 4 to 29 weeks by retinal histology, electroretinogram (ERG), and a-wave transduction modeling.

RESULTS

Both line 1 (faster degeneration) and line 3 (slower degeneration) showed progressive rod outer segment (ROS) shortening and outer nuclear layer (ONL) cell loss with age. ERG b-wave maximum amplitude (Vb(max)) decreased with age, but b-wave threshold remained constant within each line despite progressive ONL thinning and ROS shortening. The only exception was in line 1 at 29 weeks, which showed a slight threshold change relative to earlier ages. Va(max) and a-wave threshold changed more rapidly and were more sensitive than the b-wave in reflecting histologic degeneration. Va(max) was linearly proportional to the product of (ROS x ONL) across a two log unit range of data combined from both lines. The photopic b-wave was normal for both lines until the ONL thinned beyond 50%. Phototransduction sensitivity was normal for both lines, and dark-adaptation recovery after bleaching rhodopsin was normal.

CONCLUSIONS

The P23H transgenic rat has a slow rod degeneration with initially normal cone function, consistent with clinical findings of P23H patients. However, the normal bleach recovery and the normal phototransduction sensitivity in this rat model are different from human P23H disease. a-Wave measures were more sensitive than the b-wave for tracking changes. b-Wave threshold was inexplicably poor for tracking degeneration. Although line 1 degenerated faster than line 3, the functional-structural correlates were the same. The tight linear relationship between saturated a-wave amplitude and the product of (ROS x ONL) indicates that the density of cGMP-gated channels per unit ROS plasma membrane area remains constant over a wide range of degenerations.

Structural and functional rescue of murine rod photoreceptors by human rhodopsin transgene

Mice carrying a targeted disruption of the rhodopsin gene develop a severe degenerative retinopathy, failing to elaborate rod photoreceptor outer segments (ROS), having no recordable rod electroretinogram (ERG) and losing all of their rod cells over a period of approximately 12 weeks. Murine and human rhodopsins differ in their amino acid sequences. Whether, or to what extent, such variability might influence the ability of human rhodopsin to serve as an adequate structural and functional substitute for the endogenous protein in mouse rod cells bears direct relevance to exploiting the full utility of Rho-/-animals as a model of degenerative retinal disease in man. We crossed Rho-/-mice with mice expressing a wild-type human rhodopsin transgene at levels approximating to those of the endogenous protein. Immunohistological examination of retinal selections from such animals demonstrated ROS of normal number and length and temporal expression of rhodopsin similar to that observed in wild-type animals; that is, immunoreactivity to an anti-rhodopsin antibody became clearly evident by day 3 post-partum. Whereas Rho-/-mice never display a rod ERG response, and even lose cone responses by 12 weeks of age, rescued mice showed 75% normal maximum amplitudes and had ERG b-wave thresholds (based on a 50 microV criterion) within 0.1 log unit of normal wild-type at 20 weeks, and cone amplitudes remained normal at this age. These data demonstrate very substantial structural and functional rescue of the rod photoreceptors of Rho-/-mice and long-term preservation by the human rhodopsin transgene.