Complexity of the Class B Phenotype in Autosomal Dominant Retinitis Pigmentosa Due to Rhodopsin Mutations

Treatment Strategy With Gene Editing for Late-Onset Retinal Degeneration Caused by a Founder Variant in C1QTNF5

Purpose

Genome editing is an emerging group of technologies with the potential to ameliorate dominant, monogenic human diseases such as late-onset retinal degeneration (L-ORD). The goal of this study was to identify disease stages and retinal locations optimal for evaluating the efficacy of a future genome editing trial.

Methods

Twenty five L-ORD patients (age range, 33-77 years; median age, 59 years) harboring the founder variant S163R in C1QTNF5 were enrolled from three centers in the United Kingdom and United States. Patients were examined with widefield optical coherence tomography (OCT) and chromatic perimetry under dark-adapted and light-adapted conditions to derive phenomaps of retinal disease. Results were analyzed with a model of a shared natural history of a single delayed exponential across all subjects and all retinal locations.

Results

Critical age for the initiation of photoreceptor loss ranged from 48 years at the temporal paramacular retina to 74 years at the inferior midperipheral retina. Subretinal deposits (sRET-Ds) became more prevalent as critical age was approached. Subretinal pigment epithelial deposits (sRPE-Ds) were detectable in the youngest patients showing no other structural or functional abnormalities at the retina. The sRPE-D thickness continuously increased, reaching 25 µm in the extrafoveal retina and 19 µm in the fovea at critical age. Loss of light sensitivity preceded shortening of outer segments and loss of photoreceptors by more than a decade.

Conclusions

Retinal regions providing an ideal treatment window exist across all severity stages of L-ORD.

Genetic treatment for autosomal dominant inherited retinal dystrophies: approaches, challenges and targeted genotypes

Inherited retinal diseases (IRDs) have been in the front line of gene therapy development for the last decade, providing a useful platform to test novel therapeutic approaches. More than 40 clinical trials have been completed or are ongoing, tackling autosomal recessive and X-linked conditions, mostly through adeno-associated viral vector delivery of a normal copy of the disease-causing gene. However, only recently has autosomal dominant (ad) disease been targeted, with the commencement of a trial for rhodopsin (RHO)-associated retinitis pigmentosa (RP), implementing antisense oligonucleotide (AON) therapy, with promising preliminary results (NCT04123626).Autosomal dominant RP represents 15%-25% of all RP, with RHO accounting for 20%-30% of these cases. Autosomal dominant macular and cone-rod dystrophies (MD/CORD) correspond to approximately 7.5% of all IRDs, and approximately 35% of all MD/CORD cases, with the main causative gene being BEST1 Autosomal dominant IRDs are not only less frequent than recessive, but also tend to be less severe and have later onset; for example, an individual with RHO-adRP would typically become severely visually impaired at an age 2-3 times older than in X-linked RPGR-RP.Gain-of-function and dominant negative aetiologies are frequently seen in the prevalent adRP genes RHO, RP1 and PRPF31 among others, which would not be effectively addressed by gene supplementation alone and need creative, novel approaches. Zinc fingers, RNA interference, AON, translational read-through therapy, and gene editing by clustered regularly interspaced short palindromic repeats/Cas are some of the strategies that are currently under investigation and will be discussed here.

Genotype and phenotype characteristics of RHO-associated retinitis pigmentosa in the Japanese population

PURPOSE

To identify the genotypic and phenotypic characteristics of rhodopsin (RHO)-associated retinitis pigmentosa (RP) in the Japanese population.

STUDY DESIGN

Cross-sectional, single-center study METHODS: The medical records of 1336 patients with RP who underwent genetic testing at our clinic between November 2008 and September 2021 were reviewed, and patients with RHO variants were included. The patients were divided into class A and class B to assess genotype-phenotype correlations based on previous reports. The clinical findings, including best-corrected visual acuity (BCVA), OCT parameters (ellipsoid zone [EZ] width and central retinal thickness [CRT]), and presence of macular degeneration, of the 2 groups were compared.

RESULTS

The study included 28 patients diagnosed with RHO-associated RP (class A, 19; class B, 9). The BCVA was significantly worse in class A patients than in class B patients (P = 0.045). Superior EZ width was significantly shorter in class A than in class B patients (P = 0.016). Class A patients tended to have thinner CRT and shorter inferior EZ width than those of class B patients, although this difference was not significant. Macular degeneration was observed in 61.5% of class A and 12.5% of class B patients, demonstrating that macular degeneration can be a common complication in class A variants.

CONCLUSION

Patients with class A variants presented with a severer form of RP than that of patients with class B variants in the Japanese population. These results suggest that the phenotype of RHO-associated RP is linked to the location of the variants and that such a genotype-phenotype correlation is less affected by ethnicities with different genetic backgrounds.

Photoreceptor function and structure in retinal degenerations caused by biallelic BEST1 mutations

The only approved retinal gene therapy is for biallelic RPE65 mutations which cause a recessive retinopathy with a primary molecular defect located at the retinal pigment epithelium (RPE). For a distinct recessive RPE disease caused by biallelic BEST1 mutations, a pre-clinical proof-of-concept for gene therapy has been demonstrated in canine eyes. The current study was undertaken to consider potential outcome measures for a BEST1 clinical trial in patients demonstrating a classic autosomal recessive bestrophinopathy (ARB) phenotype. Spatial distribution of retinal structure showed a wide expanse of abnormalities including large intraretinal cysts, shallow serous retinal detachments, abnormalities of inner and outer segments, and an unusual prominence of the external limiting membrane. Surrounding the central macula extending from 7 to 30 deg eccentricity, outer nuclear layer was thicker than expected from a cone only retina and implied survival of many rod photoreceptors. Co-localized however, were large losses of rod sensitivity despite preserved cone sensitivities. The dissociation of rod function from rod structure observed, supports a large treatment potential in the paramacular region for biallelic bestrophinopathies.

Photoreceptor Function and Structure in Autosomal Dominant Vitelliform Macular Dystrophy Caused by BEST1 Mutations

Purpose

The purpose of this study was to evaluate rod and cone function and outer retinal structure within macular lesions, and surrounding extralesional areas of patients with autosomal dominant Best vitelliform macular dystrophy caused by BEST1 mutations.

Methods

Seventeen patients from seven families were examined with dark- and light-adapted chromatic perimetry and optical coherence tomography. Subsets of patients had long-term follow-up (14-22 years, n = 6) and dark-adaptation kinetics measured (n = 5).

Results

Within central lesions with large serous retinal detachments, rod sensitivity was severely reduced but visual acuity and cone sensitivity were relatively retained. In surrounding extralesional areas, there was a mild but detectable widening of the subretinal space in some patients and some retinal areas. Available evidence was consistent with subretinal widening causing slower dark-adaptation kinetics. Over long-term follow-up, some eyes showed formation of de novo satellite lesions at retinal locations that years previously demonstrated subretinal widening. A subclinical abnormality consisting of a retina-wide mild thickening of the outer nuclear layer was evident in many patients and thickening increased in the subset of patients with long-term follow-up.

Conclusions

Outcome measures for future clinical trials should include evaluations of rod sensitivity within central lesions and quantitative measures of outer retinal structure in normal-appearing regions surrounding the lesions.

Macular Rod Function in Retinitis Pigmentosa Measured With Scotopic Microperimetry

Purpose

To investigate the validity and reliability of macular rod photoreceptor function measurement with a microperimeter.

Methods

Macular sensitivity in dark-adapted retinitis pigmentosa (RP) patients (22 eyes; 9–67 years of age) and controls (five eyes; 22–55 years of age) was assessed with a modified Humphrey field analyzer (mHFA), as well as a scotopic microperimeter (Nidek MP-1S). Sensitivity loss (SL) was estimated at rod-mediated locations. All RP eyes were re-evaluated at a second visit 6 months later. The dynamic range of the MP-1S was expanded with a range of neutral-density filters (NDFs).

Results

In controls, a 4 NDF was used at all macular locations tested. In patients with RP, 0 to 3 NDFs were used, depending on the local disease severity. At rod-mediated locations (n = 281), SL estimates obtained with the MP-1S were highly correlated (r = 0.80) with those of the mHFA. The inter-perimeter difference of SL averaged less than 3 decibels (dB) with all NDFs, except those with most severe locations evaluated with a 0 NDF, where the difference averaged more than 6 dB. The results were similar on the second visit.

Conclusions

The MP-1S estimates of SL are highly correlated with those of the mHFA over a wide range of disease severity replicated at two visits; however, there was an unexplained bias in the magnitude of SL estimated by the MP-1S especially at loci with severe disease.

Translational Relevance

MP-1S scotopic microperimetry can be used to evaluate changes to macular rod function, but evaluation of treatment potential by quantitative comparison of SL to retinal structure will be more challenging.

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

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

Measures of Function and Structure to Determine Phenotypic Features, Natural History, and Treatment Outcomes in Inherited Retinal Diseases

Inherited retinal diseases (IRDs) are at the forefront of innovative gene-specific treatments because of the causation by single genes, the availability of microsurgical access for treatment delivery, and the relative ease of quantitative imaging and vision measurement. However, it is not always easy to choose a priori, from scores of potential measures, an appropriate subset to evaluate efficacy outcomes considering the wide range of disease stages with different phenotypic features. This article reviews measurements of visual function and retinal structure that our group has used over the past three decades to understand the natural history of IRDs. We include measures of light sensitivity, retinal structure, mapping of natural fluorophores, evaluation of pupillary light reflex, and oculomotor control. We provide historical context and examples of applicability. We also review treatment trial outcomes using these measures of function and structure. Expected final online publication date for the Annual Review of Vision Science, Volume 7 is September 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Safety and improved efficacy signals following gene therapy in childhood blindness caused by GUCY2D mutations

A first-in-human clinical trial of gene therapy in Leber congenital amaurosis due to mutations in the GUCY2D gene is underway, and early results are summarized. A recombinant adeno-associated virus serotype 5 (rAAV5) vector carrying the human GUCY2D gene was delivered by subretinal injection to one eye in three adult patients with severe visual loss, nystagmus, but preserved retinal structure. Safety and efficacy parameters were monitored for 9 months post-operatively. No systemic toxicity was detected; there were no serious adverse events, and ocular adverse events resolved. P1 and P2 showed statistically significant rod photoreceptor vision improvement by full-field stimulus testing in the treated eye. P1 also showed improvement in pupillary responses. Visual acuity remained stable from baseline in P1 and P2. P3, however, showed a gain of 0.3 logMAR in the treated eye, indicating greater cone-photoreceptor function. The results show safety and both rod- and cone-mediated efficacy of this therapy.

Rod Photoreceptor Neuroprotection in Dark-Reared Pde6brd10 Mice

Purpose

The purpose of this study was to test the hypothesis that anti-oxidant and / or anti-inflammation drugs that suppress rod death in cyclic light-reared Pde6brd10 mice are also effective in dark-reared Pde6brd10 mice.

Methods

In untreated dark-reared Pde6brd10 mice at post-natal (P) days 23 to 24, we measured the outer nuclear layer (ONL) thickness (histology) and dark-light thickness difference in external limiting membrane-retinal pigment epithelium (ELM-RPE) (optical coherence tomography [OCT]), retina layer oxidative stress (QUEnch-assiSTed [QUEST] magnetic resonance imaging [MRI]); and microglia/macrophage-driven inflammation (immunohistology). In dark-reared P50 Pde6brd10 mice, ONL thickness was measured (OCT) in groups given normal chow or chow admixed with methylene blue (MB) + Norgestrel (anti-oxidant, anti-inflammatory), or MB or Norgestrel separately.

Results

P24 Pde6brd10 mice showed no significant dark-light ELM-RPE response in superior and inferior retina consistent with high cGMP levels. Norgestrel did not significantly suppress the oxidative stress of Pde6brd10 mice that is only found in superior central outer retina of males at P23. Overt rod degeneration with microglia/macrophage activation was observed but only in the far peripheral superior retina in male and female P23 Pde6brd10 mice. Significant rod protection was measured in female P50 Pde6brd10 mice given 5 mg/kg/day MB + Norgestrel diet; no significant benefit was seen with MB chow or Norgestrel chow alone, nor in similarly treated male mice.

Conclusions

In early rod degeneration in dark-reared Pde6brd10 mice, little evidence is found in central retina for spatial associations among biomarkers of the PDE6B mutation, oxidative stress, and rod death; neuroprotection at P50 was limited to a combination of anti-oxidant/anti-inflammation treatment in a sex-specific manner.

Clinical and genetic findings in Italian patients with sector retinitis pigmentosa

Purpose

To describe clinical and genetic features in a series of Italian patients with sector retinitis pigmentosa (sector RP).

Methods

Fifteen patients with sector RP were selected from the database of Hereditary Retinal Degenerations Referring Center of Careggi Hospital (Florence, Italy). Eleven patients from five independent pedigrees underwent genetic analysis with next-generation sequencing (NGS) confirmed with Sanger sequencing. The diagnosis of sector RP was based on the detection of topographically limited retinal abnormalities consistent with corresponding sectorial visual field defects. Best-corrected visual acuity (BCVA), fundus color pictures as well as fundus autofluorescence (FAF), spectral domain-optical coherence tomography (SD-OCT), full-field electroretinography (ERG), and 30-2 Humphrey visual field (VF) data were retrospectively collected and analyzed.

Results

For the 30 eyes, the mean BCVA was 0.05 ± 0.13 logMAR, and the mean refractive error was -0.52 ± 1.89 D. The inferior retina was the most affected sector (86.7%), and the VF defect corresponded to the affected sector. FAF showed a demarcation line of increased autofluorescence between the healthy and affected retina, corresponding on SD-OCT to an interruption of the ellipsoid zone (EZ) band in the diseased retina. Dark-adapted ERG amplitudes were decreased in comparison to normative values. In five unrelated families, the sector RP phenotype was associated with sequence variants in the RHO gene. The same mutation c.568G>A p.(Asp190Asn) was found in nine patients of four families.

Conclusions

Typical sector RP is a mild form of RP characterized by preserved visual acuity with limited retinal involvement and, generally, a more favorable prognosis than other forms of RP.

Phenocopy of a heterozygous carrier of X-linked retinitis pigmentosa due to mosaicism for a RHO variant

We describe both phenotype and pathogenesis in two male siblings with typical retinitis pigmentosa (RP) and the potentially X-linked RP (XLRP) carrier phenotype in their mother. Two affected sons, two unaffected daughters, and their mother underwent detailed ophthalmological assessments including Goldmann perimetry, color vision testing, multimodal imaging and ISCEV-standard electroretinography. Genetic testing consisted of targeted next-generation sequencing (NGS) of known XLRP genes and whole exome sequencing (WES) of known inherited retinal disease genes (RetNet-WES). Variant validation and segregation analysis were performed by Sanger sequencing. The mutational load of the RHO variant in the mother was assessed in DNA from leucocytes, buccal cells and hair follicles using targeted NGS. Both affected sons showed signs of classical RP, while the mother displayed patches of hyperautofluorescence on blue light autofluorescence imaging and regional, intraretinal, spicular pigmentation, reminiscent of a carrier phenotype of XLRP. XLRP testing was negative. RetNet-WES testing revealed RHO variant c.404G > C p.(Arg135Pro) in a mosaic state (21% of the reads) in the mother and in a heterozygous state in both sons. Targeted NGQSS of the RHO variant in different maternal tissues showed a mutation load between 25.06% and 41.72%. We report for the first time that somatic mosaicism of RHO variant c.404G > C p.(Arg135Pro) mimics the phenotype of a female carrier of XLRP, in combination with heterozygosity for the variant in the two affected sons.

Clinical trial design for neuroprotection in RHO autosomal dominant retinitis pigmentosa; outcome measure considerations

Purpose: To identify structural and functional outcome measures among patients with Rho-positive autosomal dominant Retinitis Pigmentosa (adRP) to aid neuroprotection trial design.Methods: This was a retrospective cohort study of 52 patients with Rho-positive adRP. We measured Goldmann Visual Fields (GVF) constriction in four sectors (nasal, temporal, inferior, superior), and sectoral Ellipsoid Zone (EZ) width degeneration using Spectral Domain Optical Coherence Tomography (OCT) scans. Disease progression trajectories were projected using mixed effects modeling.Results: Superior GVF was most constricted at presentation and had the shallowest trajectory (less steep negative slope); Inferior GVF was less constricted (corrected p < .001) and had a steeper negative slope (corrected p = .019) than superior GVF. Temporal EZ was most stable on OCT with a relatively shallow negative trajectory (corrected p = .011).Conclusions: Patients' superior visual fields presented with more constriction and subsequently had a shallow negative slope suggesting the corresponding inferior retina may be "burned out" at presentation. Targeted therapies for adRP will likely show a greater efficacy signal if delivered to the superior and nasal retina, which may demonstrate more change on OCT and GVF over the course of a neuroprotection trial.Translational Relevance: Mixed effects analysis of sectoral visual field constriction and EZ degeneration in Rho-positive adRP can prove useful in monitoring therapeutic efficacy and identifying targets for local therapies.

Rod function deficit in retained photoreceptors of patients with class B Rhodopsin mutations

A common inherited retinal disease is caused by mutations in RHO expressed in rod photoreceptors that provide vision in dim ambient light. Approximately half of all RHO mutations result in a Class B phenotype where mutant rods are retained in some retinal regions but show severe degeneration in other regions. We determined the natural history of dysfunction and degeneration of retained rods by serially evaluating patients. Even when followed for more than 20 years, rod function and structure at some retinal locations could remain unchanged. Other locations showed loss of both vision and photoreceptors but the rate of rod vision loss was greater than the rate of photoreceptor degeneration. This unexpected divergence in rates with disease progression implied the development of a rod function deficit beyond loss of cells. The divergence of progression rates was also detectable over a short interval of 2 years near the health-disease transition in the superior retina. A model of structure–function relationship supported the existence of a large rod function deficit which was also most prominent near regions of health-disease transition. Our studies support the realistic therapeutic goal of improved night vision for retinal regions specifically preselected for rod function deficit in patients.

Retinal Dystrophies and the Road to Treatment: Clinical Requirements and Considerations

: Retinal dystrophies (RDs) comprise relatively rare but devastating causes of progressive vision loss. They represent a spectrum of diseases with marked genetic and clinical heterogeneity. Mutations in the same gene may lead to different diagnoses, for example, retinitis pigmentosa or cone dystrophy. Conversely, mutations in different genes may lead to the same phenotype. The age at symptom onset, and the rate and characteristics of peripheral and central vision decline, may vary widely per disease group and even within families. For most RD cases, no effective treatment is currently available. However, preclinical studies and phase I/II/III gene therapy trials are ongoing for several RD subtypes, and recently the first retinal gene therapy has been approved by the US Food and Drug Administration for RPE65-associated RDs: voretigene neparvovec-rzyl (Luxturna). With the rapid advances in gene therapy studies, insight into the phenotypic spectrum and long-term disease course is crucial information for several RD types. The vast clinical heterogeneity presents another important challenge in the evaluation of potential efficacy in future treatment trials, and in establishing treatment candidacy criteria. This perspective describes these challenges, providing detailed clinical descriptions of several forms of RD that are caused by genes of interest for ongoing and future gene or cell-based therapy trials. Several ongoing and future treatment options will be described.

Autosomal Dominant Retinitis Pigmentosa Due to Class B Rhodopsin Mutations: An Objective Outcome for Future Treatment Trials

Gene therapy for adRP due to RHO mutations was recently shown to prevent photoreceptor death in a canine model of Class B disease. Among translational steps to be taken, one is to determine a method to detect efficacy in a human clinical trial. The relatively slow progression of adRP becomes a difficulty for clinical trials requiring an answer to whether there is slowed progression of degeneration in response to therapy. We performed a single-center, retrospective observational study of cross-sectional and longitudinal data. The study was prompted by our identification of a pericentral disease distribution in Class B RHO-adRP. Ultrawide optical coherence tomography (OCT) scans were used. Inferior retinal pericentral defects was an early disease feature. Degeneration further inferior in the retina merged with the pericentral defect, which extended into superior retina. In about 70% of patients, there was an asymmetric island of structure with significantly greater superior than inferior ellipsoid zone (EZ) extent. Serial measures of photoreceptor structure by OCT indicated constriction in superior retinal extent within a two-year interval. We conclude that these results should allow early-phase trials of therapy in RHO-adRP to move forward by inclusion of patients with an asymmetric extent of photoreceptor structure and by monitoring therapeutic effects over two years in the superior retina, a reasonable target for subretinal injection.

Clinically Relevant Outcome Measures for the I307N Rhodopsin Mouse: A Model of Inducible Autosomal Dominant Retinitis Pigmentosa

Purpose

The I307N rhodopsin (Rho) mouse is a light-inducible model of autosomal dominant retinitis pigmentosa (adRP) that may be useful in testing therapies. We investigated the time-course of retinal changes of the I307N Rho mouse with spectral-domain optical coherence tomography (SD-OCT).

Methods

SD-OCT was performed up to day 30 after light damage; electroretinography (ERG) was employed to evaluate photoreceptor function. We utilized ImageJ to analyze reflectivity of the retina. We used light and electron microscopy to assess retinal organization. We stained synaptophysin and zonula occludins-1 with immunohistochemistry to determine injury to the plexiform layers and retinal pigment epithelium (RPE). We performed lectin staining to evaluate retinal blood vessels.

Results

Retinal degeneration increased with longer exposures to light. An increase in retinal thickness was detected by SD-OCT on day 1 after light challenge followed by loss of the outer nuclear layer (ONL) by day 8. Degeneration was most severe in the nasal and inferior retina. Hyper-reflectivity on SD-OCT developed as early as 1 day after light exposure. Disorganization of the ONL, condensation of photoreceptor chromatin, disruption of the outer limiting membrane, and disarray of outer segments were associated with the hyper-reflectivity. Retraction of the outer plexiform synapses and resorption of the subretinal detachment contributed to retinal thinning. The RPE remained intact, whereas atrophied major retinal vessels were evident after light damage.

Conclusions

Our time-course analysis of retinal degeneration in the I307N Rho mouse with SD-OCT and other outcome measures should enable the use of the mouse model in preclinical efficacy studies and mechanistic studies.

Translational Retinal Research and Therapies

The following review summarizes the state of the art in representative aspects of gene therapy/translational medicine and evolves from a symposium held at the School of Veterinary Medicine, University of Pennsylvania on November 16, 2017 honoring Dr. Gustavo Aguirre, recipient of ARVO's 2017 Proctor Medal. Focusing on the retina, speakers highlighted current work on moving therapies for inherited retinal degenerative diseases from the laboratory bench to the clinic.

Misfolded rhodopsin mutants display variable aggregation properties

The largest class of rhodopsin mutations causing autosomal dominant retinitis pigmentosa (adRP) is mutations that lead to misfolding and aggregation of the receptor. The misfolding mutants have been characterized biochemically, and categorized as either partial or complete misfolding mutants. This classification is incomplete and does not provide sufficient information to fully understand the disease pathogenesis and evaluate therapeutic strategies. A Förster resonance energy transfer (FRET) method was utilized to directly assess the aggregation properties of misfolding rhodopsin mutants within the cell. Partial (P23H and P267L) and complete (G188R, H211P, and P267R) misfolding mutants were characterized to reveal variability in aggregation properties. The complete misfolding mutants all behaved similarly, forming aggregates when expressed alone, minimally interacting with the wild-type receptor when coexpressed, and were unresponsive to treatment with the pharmacological chaperone 9-cis retinal. In contrast, variability was observed between the partial misfolding mutants. In the opsin form, the P23H mutant behaved similarly as the complete misfolding mutants. In contrast, the opsin form of the P267L mutant existed as both aggregates and oligomers when expressed alone and formed mostly oligomers with the wild-type receptor when coexpressed. The partial misfolding mutants both reacted similarly to the pharmacological chaperone 9-cis retinal, displaying improved folding and oligomerization when expressed alone but aggregating with wild-type receptor when coexpressed. The observed differences in aggregation properties and effect of 9-cis retinal predict different outcomes in disease pathophysiology and suggest that retinoid-based chaperones will be ineffective or even detrimental.

Mutation-independent rhodopsin gene therapy by knockdown and replacement with a single AAV vector

Inherited retinal degenerations are caused by mutations in >250 genes that affect photoreceptor cells or the retinal pigment epithelium and result in vision loss. For autosomal recessive and X-linked retinal degenerations, significant progress has been achieved in the field of gene therapy as evidenced by the growing number of clinical trials and the recent commercialization of the first gene therapy for a form of congenital blindness. However, despite significant efforts to develop a treatment for the most common form of autosomal dominant retinitis pigmentosa (adRP) caused by >150 mutations in the rhodopsin (RHO) gene, translation to the clinic has stalled. Here, we identified a highly efficient shRNA that targets human (and canine) RHO in a mutation-independent manner. In a single adeno-associated viral (AAV) vector we combined this shRNA with a human RHO replacement cDNA made resistant to RNA interference and tested this construct in a naturally occurring canine model of RHO-adRP. Subretinal vector injections led to nearly complete suppression of endogenous canine RHO RNA, while the human RHO replacement cDNA resulted in up to 30% of normal RHO protein levels. Noninvasive retinal imaging showed photoreceptors in treated areas were completely protected from retinal degeneration. Histopathology confirmed retention of normal photoreceptor structure and RHO expression in rod outer segments. Long-term (>8 mo) follow-up by retinal imaging and electroretinography indicated stable structural and functional preservation. The efficacy of this gene therapy in a clinically relevant large-animal model paves the way for treating patients with RHO-adRP.

The Genetic Basis of Pericentral Retinitis Pigmentosa-A Form of Mild Retinitis Pigmentosa

Pericentral retinitis pigmentosa (RP) is an atypical form of RP that affects the near-peripheral retina first and tends to spare the far periphery. This study was performed to further define the genetic basis of this phenotype. We identified a cohort of 43 probands with pericentral RP based on a comprehensive analysis of their retinal phenotype. Genetic analyses of DNA samples from these patients were performed using panel-based next-generation sequencing, copy number variations, and whole exome sequencing (WES). Mutations provisionally responsible for disease were found in 19 of the 43 families (44%) analyzed. These include mutations in RHO (five patients), USH2A (four patients), and PDE6B (two patients). Of 28 putatively pathogenic alleles, 15 (54%) have been previously identified in patients with more common forms of typical RP, while the remaining 13 mutations (46%) were novel. Burden testing of WES data successfully identified HGSNAT as a cause of pericentral RP in at least two patients, suggesting it is also a relatively common cause of pericentral RP. While additional sequencing might uncover new genes specifically associated with pericentral RP, the current results suggest that genetically pericentral RP is not a separate clinical entity, but rather is part of the spectrum of mild RP phenotypes.

Defining Outcomes for Clinical Trials of Leber Congenital Amaurosis Caused by GUCY2D Mutations

PURPOSE

To determine outcome measures for a clinical trial of Leber congenital amaurosis (LCA) associated with mutations in the GUCY2D gene.

DESIGN

Retrospective observational case series.

METHODS

Twenty-eight patients with GUCY2D-LCA (aged 2-59 years) were studied clinically and with chromatic full-field sensitivity testing (FST), optical coherence tomography (OCT), pupillometry, and the NEI Visual Function Questionnaire (VFQ).

RESULTS

FST permitted quantitation of cone and rod sensitivity in these patients with severe visual impairment. For most patients, the degree of rod and cone sensitivity losses showed a relationship, thereby providing an opportunity to divide patients into cohorts by severity of rod and cone dysfunction. OCT analyses indicated that retinal structure could be used not only as an objective safety measure but also as an exploratory efficacy outcome. A foveal bulge was not present in 67% of patients. The intensity of inner segment/outer segment (ellipsoid zone line) reflectivity was reduced significantly at the fovea and in the rod-dense superior retina. Based on OCT and FST parameters, most patients had dissociation of structure and function. Abnormal pupillometry sensitivity in the majority of GUCY2D-LCA patients provided another objective efficacy outcome. NEI VFQ scores showed a similar range of findings to those of other severe retinal diseases.

CONCLUSION

Conventional outcome measures, such as visual acuity and the NEI VFQ, will need to be complemented by methods more specific to this GUCY2D-LCA population. Any therapeutic strategy should determine if there is an effect on rod as well as cone function and structure. FST provides a photoreceptor-based subjective outcome; and OCT in 2 retinal regions, fovea and superior retina, can assess photoreceptor structure. A change in the relationship of structure and function away from baseline becomes evidence of efficacy.