Choroideremia Gene Therapy Phase 2 Clinical Trial: 24-Month Results

Structural evaluation in inherited retinal diseases

Ophthalmic genetics is a field that has been rapidly evolving over the last decade, mainly due to the flourishing of translational medicine for inherited retinal diseases (IRD). In this review, we will address the different methods by which retinal structure can be objectively and accurately assessed in IRD. We review standard-of-care imaging for these patients: colour fundus photography, fundus autofluorescence imaging and optical coherence tomography (OCT), as well as higher-resolution and/or newer technologies including OCT angiography, adaptive optics imaging, fundus imaging using a range of wavelengths, magnetic resonance imaging, laser speckle flowgraphy and retinal oximetry, illustrating their utility using paradigm genotypes with on-going therapeutic efforts/trials.

The safety and efficacy of gene therapy treatment for monogenic retinal and optic nerve diseases: A systematic review

PURPOSE

This study aimed to systematically review and summarize gene therapy treatment for monogenic retinal and optic nerve diseases.

METHODS

This review was prospectively registered (CRD42021229812). A comprehensive literature search was performed in Ovid MEDLINE, Ovid Embase, Cochrane Central, and clinical trial registries (February 2021). Clinical studies describing DNA-based gene therapy treatments for monogenic posterior ocular diseases were eligible for inclusion. Risk of bias evaluation was performed. Data synthesis was undertaken applying Synthesis Without Meta-analysis guidelines.

RESULTS

This study identified 47 full-text publications, 50 conference abstracts, and 54 clinical trial registry entries describing DNA-based ocular gene therapy treatments for 16 different genetic variants. Study summaries and visual representations of safety and efficacy outcomes are presented for 20 unique full-text publications in RPE65-mediated retinal dystrophies, choroideremia, Leber hereditary optic neuropathy, rod-cone dystrophy, achromatopsia, and X-linked retinoschisis. The most common adverse events were related to lid/ocular surface/cornea abnormalities in subretinal gene therapy trials and anterior uveitis in intravitreal gene therapy trials.

CONCLUSION

There is a high degree of variability in ocular monogenic gene therapy trials with respect to study design, statistical methodology, and reporting of safety and efficacy outcomes. This review improves the accessibility and transparency in interpreting gene therapy trials to date.

Risk Mitigation of Immunogenicity: A Key to Personalized Retinal Gene Therapy

Gene therapy (GT) for ocular disorders has advanced the most among adeno-associated virus (AAV)-mediated therapies, with one product already approved in the market. The bank of retinal gene mutations carefully compiled over 30 years, the small retinal surface that does not require high clinical vector stocks, and the relatively immune-privileged environment of the eye explain such success. However, adverse effects due to AAV-delivery, though rare in the retina have led to the interruption of clinical trials. Risk mitigation, as the key to safe and efficient GT, has become the focus of 'bedside-back-to-bench' studies. Herein, we overview the inflammatory adverse events described in retinal GT trials and analyze which components of the retinal immunological environment might be the most involved in these immune responses, with a focus on the innate immune system composed of microglial surveillance. We consider the factors that can influence inflammation in the retina after GT such as viral sensors in the retinal tissue and CpG content in promoters or transgene sequences. Finally, we consider options to reduce the immunological risk, including dose, modified capsids or exclusion criteria for clinical trials. A better understanding and mitigation of immune risk factors inducing host immunity in AAV-mediated retinal GT is the key to achieving safe and efficient GT.

Current trends in gene therapy for retinal diseases (Review)

The eye is considered an effective target for genetic therapy, as it has a privileged immune status, it is easily accessed for medication delivery and it is affected by a number of inherited disorders. In particular, the retina is considered for gene therapy due to the fact that it can be visualized with ease, it does not have lymphatic vessels, nor a direct blood network for the outer layers and its cells do not divide after birth, and thus transgene expression is not affected. As gene therapy is currently on a continuously progressive development trend, this emerging field of gene manipulation techniques has yielded promising results. This involves the development of treatments for a number of debilitating and blinding diseases, which were to date considered intractable. However, numerous unanswered questions remain as regards the long-term efficacy and safety profile of these treatments. The present review article discusses the current research status regarding genetic manipulation techniques aimed at addressing visual impairment related to retinal disorders, both inherited and degenerative.

Gene Therapy in Inherited Retinal Diseases: An Update on Current State of the Art

Background: Gene therapy cannot be yet considered a far perspective, but a tangible therapeutic option in the field of retinal diseases. Although still confined in experimental settings, the preliminary results are promising and provide an overall scenario suggesting that we are not so far from the application of gene therapy in clinical settings. The main aim of this review is to provide a complete and updated overview of the current state of the art and of the future perspectives of gene therapy applied on retinal diseases.

Methods: We carefully revised the entire literature to report all the relevant findings related to the experimental procedures and the future scenarios of gene therapy applied in retinal diseases. A clinical background and a detailed description of the genetic features of each retinal disease included are also reported.

Results: The current literature strongly support the hope of gene therapy options developed for retinal diseases. Although being considered in advanced stages of investigation for some retinal diseases, such as choroideremia (CHM), retinitis pigmentosa (RP), and Leber's congenital amaurosis (LCA), gene therapy is still quite far from a tangible application in clinical practice for other retinal diseases.

Conclusions: Gene therapy is an extremely promising therapeutic tool for retinal diseases. The experimental data reported in this review offer a strong hope that gene therapy will be effectively available in clinical practice in the next years.

Molecular Therapy for Choroideremia: Pre-clinical and Clinical Progress to Date

Choroideremia is an inherited retinal disease characterised by a degeneration of the light-sensing photoreceptors, supporting retinal pigment epithelium and underlying choroid. Patients present with the same symptoms as those with classic rod-cone dystrophy: (1) night blindness early in life; (2) progressive peripheral visual field loss, and (3) central vision decline with a slow progression to legal blindness. Choroideremia is monogenic and caused by mutations in CHM. Eight clinical trials (three phase 1/2, four phase 2, and one phase 3) have started (four of which are already finished) to evaluate the therapeutic efficacy of gene supplementation mediated by subretinal delivery of an adeno-associated virus serotype 2 (AAV2/2) vector expressing CHM. Furthermore, one phase 1 clinical trial has been initiated to evaluate the efficiency of a novel AAV variant to deliver CHM to the outer retina following intravitreal delivery. Lastly, a non-viral-mediated CHM replacement strategy is currently under development, which could lead to a future clinical trial. Here, we summarise the rationale behind these various studies, as well as any results published to date. The diversity of these trials currently places choroideremia at the forefront of the retinal gene therapy field. As a consequence, the trial outcomes, regardless of the results, have the potential to change the landscape of gene supplementation for inherited retinal diseases.

Gene therapy for inherited retinal diseases

Inherited retinal diseases (IRDs) are a genetically variable collection of devastating disorders that lead to significant visual impairment. Advances in genetic characterization over the past two decades have allowed identification of over 260 causative mutations associated with inherited retinal disorders. Thought to be incurable, gene supplementation therapy offers great promise in treating various forms of these blinding conditions. In gene replacement therapy, a disease-causing gene is replaced with a functional copy of the gene. These therapies are designed to slow disease progression and hopefully restore visual function. Gene therapies are typically delivered to target retinal cells by subretinal (SR) or intravitreal (IVT) injection. The historic Food and Drug Administration (FDA) approval of voretigene neparvovec for RPE65-associated Leber's congenital amaurosis (LCA) spurred tremendous optimism surrounding retinal gene therapy for various other monogenic IRDs. Novel disease-causing mutations continue to be discovered annually, and targeted genetic therapy is now under development in clinical and preclinical models for many IRDs. Numerous clinical trials for other IRDs are ongoing or have recently completed. Disorders being targeted for genetic therapy include retinitis pigmentosa (RP), choroideremia (CHM), achromatopsia (ACHM), Leber's hereditary optic neuropathy, usher syndrome (USH), X-linked retinoschisis, and Stargardt disease. Here, we provide an update of completed, ongoing, and planned clinical trials using gene supplementation strategies for retinal degenerative disorders.

Precision Medicine Trials in Retinal Degenerations

The beginning of the twenty-first century was marked by the innovative use of pharmacochemical interventions, which have since expanded to include gene-based molecular therapies. For years, treatment has focused on tackling the pathophysiology of monogenic orphan diseases, and one of the first applications of these novel genome editing technologies was the treatment of rare inherited retinal dystrophies. In this review, we present recent, ongoing, and future gene therapy-based treatment trials for choroideremia, X-linked retinitis pigmentosa, Stargardt disease, and age-related macular degeneration. As these trials pave the way toward halting the progression of such devastating diseases, we will begin to see the exciting development of newer, cutting-edge strategies including base editing and prime editing, ushering in a new era of precision medicine.

cGMP-grade human iPSC-derived retinal photoreceptor precursor cells rescue cone photoreceptor damage in non-human primates

Background

Retinal regenerative therapies hold great promise for the treatment of inherited retinal degenerations (IRDs). Studies in preclinical lower mammal models of IRDs have suggested visual improvement following retinal photoreceptor precursors transplantation, but there is limited evidence on the ability of these transplants to rescue retinal damage in higher mammals. The purpose of this study was to evaluate the therapeutic potential of photoreceptor precursors derived from clinically compliant induced pluripotent stem cells (iPSCs).

Methods

Photoreceptor precursors were sub-retinally transplanted into non-human primates (Macaca fascicularis). The cells were transplanted both in naïve and cobalt chloride-induced retinal degeneration models who had been receiving systemic immunosuppression for one week prior to the procedure. Optical coherence tomography, fundus autofluorescence imaging, electroretinography, ex vivo histology and immunofluorescence staining were used to evaluate retinal structure, function and survival of transplanted cells.

Results

There were no adverse effects of iPSC-derived photoreceptor precursors on retinal structure or function in naïve NHP models, indicating good biocompatibility. In addition, photoreceptor precursors injected into cobalt chloride-induced retinal degeneration NHP models demonstrated an ability both to survive and to mature into cone photoreceptors at 3 months post-transplant. Optical coherence tomography showed restoration of retinal ellipsoid zone post-transplantation.

Conclusions

These findings demonstrate the safety and therapeutic potential of clinically compliant iPSC-derived photoreceptor precursors as a cell replacement source for future clinical trials.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02539-8.

Expression of Rab Prenylation Pathway Genes and Relation to Disease Progression in Choroideremia

Purpose

Choroideremia results from the deficiency of Rab Escort Protein 1 (REP1), encoded by CHM, involved in the prenylation of Rab GTPases. Here, we investigate whether the transcription and expression of other genes involved in the prenylation of Rab proteins correlates with disease progression in a cohort of patients with choroideremia.

Methods

Rates of retinal pigment epithelial area loss in 41 patients with choroideremia were measured using fundus autofluorescence imaging for up to 4 years. From lysates of cultured skin fibroblasts donated by patients (n = 15) and controls (n = 14), CHM, CHML, RABGGTB and RAB27A mRNA expression, and REP1 and REP2 protein expression were compared.

Results

The central autofluorescent island area loss in patients with choroideremia occurred with a mean half-life of 5.89 years (95% confidence interval [CI] = 5.09-6.70), with some patients demonstrating relatively fast or slow rates of progression (range = 3.3-14.1 years). Expression of CHM mRNA and REP1 protein were significantly decreased in all patients. No difference in expression of CHML, RABGGTB, RAB27A, or REP2 was seen between patients and controls. No correlation was seen between expression of the genes analyzed and rates of retinal degeneration. Non-sense induced transcriptional compensation of CHML, a CHM-like retrogene, was not observed in patients with CHM variants predicted to undergo non-sense mediated decay.

Conclusions

Patients with choroideremia, who are deficient for REP1, show normal levels of expression of other genes involved in Rab prenylation, which do not appear to play any modifying role in the rate of disease progression.

Translational Relevance

There remains little evidence for selection of patients for choroideremia gene therapy based on genotype.

Validating Ellipsoid Zone Area Measurement With Multimodal Imaging in Choroideremia

Purpose

To assess en face ellipsoid zone (EZ) maps of remaining retinal structure as outcome measures for the future clinical research in patients with choroideremia.

Methods

Twenty eyes from 12 patients with a confirmed genetic diagnosis of choroideremia were included retrospectively from a single site. From spectral domain-optical coherence tomography volume scans, slabs including the EZ were manually segmented to create the en face EZ maps. The preserved EZ area was measured by two graders. Lengths of the EZ were recorded at 0°, 45°, 90°, and 135°. The intraclass correlation coefficients and Bland–Altman plots were used to show intergrader agreement. The Pearson correlation coefficient evaluated the correlation between length and area. A Bland–Altman plot compared en face EZ and the preserved fundus autofluorescence area.

Results

Measurements of EZ area by two graders showed excellent agreement with an intraclass correlation coefficient of 0.992 (95% confidence interval, 0.980–0.997). A Pearson correlation analysis showed that the existing marker for preserved photoreceptor (horizontal EZ length) was correlated with the area (r = 0.722). The average EZ length in four meridians showed a much better correlation with the EZ area (r = 0.929). The fundus autofluorescence area was found to be a mean of 0.45 ± 0.99 mm² greater than the EZ area.

Conclusions

EZ area measurement provides excellent intergrader reliability, although the process is time consuming. We propose a less time-consuming alternative to estimate the EZ by using the average EZ band length in meridians. Our data also suggest that the loss of photoreceptor inner segments is an early change in choroideremia and may happen before the loss of the retinal pigment epithelium.

Translational Relevance

En face EZ mapping is a potential tool for future clinical trials to quantify preserved photoreceptor structure in choroideremia.

Effects of Altering HSPG Binding and Capsid Hydrophilicity on Retinal Transduction by AAV

Adeno-associated viruses (AAVs) have recently emerged as the leading vector for retinal gene therapy. However, AAV vectors which are capable of achieving clinically relevant levels of transgene expression and widespread retinal transduction are still an unmet need. Using rationally designed AAV2-based capsid variants, we investigate the role of capsid hydrophilicity and hydrophobicity as it relates to retinal transduction. We show that hydrophilic, single amino acid (aa) mutations (V387R, W502H, E530K, L583R) in AAV2 negatively impact retinal transduction when heparan sulfate proteoglycan (HSPG) binding remains intact. Conversely, addition of hydrophobic point mutations to an HSPG binding deficient capsid (AAV2ΔHS) lead to increased retinal transduction in both mouse and macaque. Our top performing vector, AAV2(4pMut)ΔHS, achieved robust rod and cone photoreceptor (PR) transduction in macaque, especially in the fovea, and demonstrates the ability to spread laterally beyond the borders of the subretinal injection (SRI) bleb. This study both evaluates biophysical properties of AAV capsids that influence retinal transduction, and assesses the transduction and tropism of a novel capsid variant in a clinically relevant animal model.ImportanceRationally guided engineering of AAV capsids aims to create new generations of vectors with enhanced potential for human gene therapy. By applying rational design principles to AAV2-based capsids, we evaluated the influence of hydrophilic and hydrophobic amino acid (aa) mutations on retinal transduction as it relates to vector administration route. Through this approach we identified a largely deleterious relationship between hydrophilic aa mutations and canonical HSPG binding by AAV2-based capsids. Conversely, the inclusion of hydrophobic aa substitutions on a HSPG binding deficient capsid (AAV2ΔHS), generated a vector capable of robust rod and cone photoreceptor (PR) transduction. This vector AAV2(4pMut)ΔHS also demonstrates a remarkable ability to spread laterally beyond the initial subretinal injection (SRI) bleb, making it an ideal candidate for the treatment of retinal diseases which require a large area of transduction.

An Update on Gene Therapy for Inherited Retinal Dystrophy: Experience in Leber Congenital Amaurosis Clinical Trials

Inherited retinal dystrophies (IRDs) are a group of rare eye diseases caused by gene mutations that result in the degradation of cone and rod photoreceptors or the retinal pigment epithelium. Retinal degradation progress is often irreversible, with clinical manifestations including color or night blindness, peripheral visual defects and subsequent vision loss. Thus, gene therapies that restore functional retinal proteins by either replenishing unmutated genes or truncating mutated genes are needed. Coincidentally, the eye’s accessibility and immune-privileged status along with major advances in gene identification and gene delivery systems heralded gene therapies for IRDs. Among these clinical trials, voretigene neparvovec-rzyl (Luxturna), an adeno-associated virus vector-based gene therapy drug, was approved by the FDA for treating patients with confirmed biallelic RPE65 mutation-associated Leber Congenital Amaurosis (LCA) in 2017. This review includes current IRD gene therapy clinical trials and further summarizes preclinical studies and therapeutic strategies for LCA, including adeno-associated virus-based gene augmentation therapy, 11-cis-retinal replacement, RNA-based antisense oligonucleotide therapy and CRISPR-Cas9 gene-editing therapy. Understanding the gene therapy development for LCA may accelerate and predict the potential hurdles of future therapeutics translation. It may also serve as the template for the research and development of treatment for other IRDs.

Focused Update on AAV-Based Gene Therapy Clinical Trials for Inherited Retinal Degeneration

Inherited retinal diseases (IRDs) comprise a clinically and genetically heterogeneous group of disorders that can ultimately result in photoreceptor dysfunction/death and vision loss. With over 270 genes known to be involved in IRDs, translation of treatment strategies into clinical applications has been historically difficult. However, in recent years there have been significant advances in basic research findings as well as translational studies, culminating in an increasing number of clinical trials with the ultimate goal of reducing vision loss and associated morbidities. The recent approval of Luxturna^® (voretigene neparvovec-rzyl) for Leber congenital amaurosis type 2 (LCA2) prompts a review of the current clinical trials for IRDs, with a particular focus on the importance of adeno-associated virus (AAV)-based gene therapies. The present article reviews the current state of AAV use in gene therapy clinical trials for IRDs, with a brief background on AAV and the reasons behind its dominance in ocular gene therapy. It will also discuss pre-clinical progress in AAV-based therapies aimed at treating other ocular conditions that can have hereditable links, and what alternative technologies are progressing in the same therapeutic space.

Is subretinal AAV gene replacement still the only viable treatment option for choroideremia?

INTRODUCTION

Choroideremia is an X-linked inherited retinal degeneration resulting from mutations in the CHM gene, encoding Rab escort protein-1 (REP1), a protein regulating intracellular vesicular transport. Loss-of-function mutations in CHM lead to progressive loss of retinal pigment epithelium (RPE) with photoreceptor and choriocapillaris degeneration, leading to progressive visual field constriction and loss of visual acuity. Three hundred and fifty-four unique mutations have been reported in CHM. While gene augmentation remains an ideal therapeutic option for choroideremia, other potential future clinical strategies may exist.

AREAS COVERED

The authors examine the pathophysiology and genetic basis of choroideremia. They summarize the status of ongoing gene therapy trials and discuss CHM mutations amenable to other therapeutic approaches including CRISPR/Cas-based DNA and RNA editing, nonsense suppression of premature termination codons, and antisense oligonucleotides for splice modification. The authors undertook a literature search in PubMed and NIH Clinical Trials in October 2020.

EXPERT OPINION

The authors conclude that AAV-mediated gene augmentation remains the most effective approach for choroideremia. Given the heterogeneity of CHM mutations and potential risks and benefits, genome-editing approaches currently do not offer significant advantages. Nonsense suppression strategies and antisense oligonucleotides are exciting novel therapeutic options; however, their clinical viability remains to be determined.

Inherited retinal diseases: Therapeutics, clinical trials and end points-A review

Inherited retinal diseases (IRDs) are a clinically and genetically heterogeneous group of disorders characterised by photoreceptor degeneration or dysfunction. These disorders typically present with severe vision loss that can be progressive, with disease onset ranging from congenital to late adulthood. The advances in genetics, retinal imaging and molecular biology, have conspired to create the ideal environment for establishing treatments for IRDs, with the first approved gene therapy and the commencement of multiple clinical trials. The scope of this review is to familiarise clinicians and scientists with the current management and the prospects for novel therapies for: (1) macular dystrophies, (2) cone and cone-rod dystrophies, (3) cone dysfunction syndromes, (4) Leber congenital amaurosis, (5) rod-cone dystrophies, (6) rod dysfunction syndromes and (7) chorioretinal dystrophies. We also briefly summarise the investigated end points for the ongoing trials.

Gene therapy for inherited retinal diseases: progress and possibilities

Inherited retinal diseases (IRDs) comprise a heterogeneous group of genetic disorders affecting the retina. Caused by mutations in over 300 genes, IRDs result in visual impairment due to dysfunction and degeneration of photoreceptors, retinal pigment epithelium, or the choroid. Important photoreceptor IRDs include retinitis pigmentosa and Leber congenital amaurosis. Macular dystrophies include Stargardt and Best disease. Currently, IRDs are largely incurable but the landscape of treatment options is rapidly changing for these diseases which, untreated, result in severe visual impairment and blindness.Advances in DNA delivery to the retina and improved genetic diagnosis of IRDs have led to a new era of research into gene therapy for these vision-threatening disorders. Gene therapy is a compelling approach due to the monogenic nature of most IRDs, with the retina being a favourable target for administering genetic vectors due to its immunoprivileged environment, direct visibility, and multiple methods to assess sensitivity and function. Generally, retinal gene therapy involves a subretinal or intravitreal injection of a viral vector, which infects target cells to deliver a therapeutic gene, or transgene. A gene augmentation strategy introduces a functioning copy of a gene to restore expression of a mutated gene, whereas a gene-editing strategy aims to directly edit and correct the mutation. Common delivery vectors include adeno-associated virus (AAV) and lentivirus.Voretigene neparvovec-rzyl (Luxturna) became the first FDA-approved direct gene therapy in December 2017, and the Australian TGA followed suit in August 2020. More are projected to follow, with clinical trials underway for many other IRDs.This review provides an overview of gene therapy for IRDs, including current progress and challenges. A companion article in this issue details target patient populations for IRD gene therapy, and how optometrists can assist in assessing individuals who may be eligible for current and future therapies.

CHM mutation spectrum and disease: An update at the time of human therapeutic trials

Choroideremia is an X-linked inherited retinal disorder (IRD) characterized by the degeneration of retinal pigment epithelium, photoreceptors, choriocapillaris and choroid affecting males with variable phenotypes in female carriers. Unlike other IRD, characterized by a large clinical and genetic heterogeneity, choroideremia shows a specific phenotype with causative mutations in only one gene, CHM. Ongoing gene replacement trials raise further interests in this disorder. We describe here the clinical and genetic data from a French cohort of 45 families, 25 of which carry novel variants, in the context of 822 previously reported choroideremia families. Most of the variants represent loss-of-function mutations with eleven families having large (i.e. ≥6 kb) genomic deletions, 18 small insertions, deletions or insertion deletions, six showing nonsense variants, eight splice site variants and two missense variants likely to affect splicing. Similarly, 822 previously published families carry mostly loss-of-function variants. Recurrent variants are observed worldwide, some of which linked to a common ancestor, others arisen independently in specific CHM regions prone to mutations. Since all exons of CHM may harbor variants, Sanger sequencing combined with quantitative polymerase chain reaction or multiplex ligation-dependent probe amplification experiments are efficient to achieve the molecular diagnosis in patients with typical choroideremia features.

Multisensory perception in Argus II retinal prosthesis patients: Leveraging auditory-visual mappings to enhance prosthesis outcomes

Crossmodal mappings associate features (such as spatial location) between audition and vision, thereby aiding sensory binding and perceptual accuracy. Previously, it has been unclear whether patients with artificial vision will develop crossmodal mappings despite the low spatial and temporal resolution of their visual perception (particularly in light of the remodeling of the retina and visual cortex that takes place during decades of vision loss). To address this question, we studied crossmodal mappings psychophysically in Retinitis Pigmentosa patients with partial visual restoration by means of Argus II retinal prostheses, which incorporate an electrode array implanted on the retinal surface that stimulates still-viable ganglion cells with a video stream from a head-mounted camera. We found that Argus II patients (N = 10) exhibit significant crossmodal mappings between auditory location and visual location, and between auditory pitch and visual elevation, equivalent to those of age-matched sighted controls (N = 10). Furthermore, Argus II patients (N = 6) were able to use crossmodal mappings to locate a visual target more quickly with auditory cueing than without. Overall, restored artificial vision was shown to interact with audition via crossmodal mappings, which implies that the reorganization during blindness and the limitations of artificial vision did not prevent the relearning of crossmodal mappings. In particular, cueing based on crossmodal mappings was shown to improve visual search with a retinal prosthesis. This result represents a key first step toward leveraging crossmodal interactions for improved patient visual functionality.

Chronic untreated retinal detachment in a patient with choroideremia provides insight into the disease process and potential therapy

AIM

We present the case of a 72-year-old male with advanced choroideremia and a left chronic rhegmatogenous retinal detachment, which to our knowledge is the first formal report of a retinal detachment in this disease.

BACKGROUND

Choroideremia is a rare X-linked inherited retinal dystrophy, caused by mutations in the CHM gene which encodes Rab escort protein 1 (REP1), and affected males typically experience a progressive centripetal loss of vision. The disease pathology is caused by a primary retinal pigment epithelium degeneration, which leads to secondary loss of photoreceptors and choriocapillaris. This in turn leads to fusion of the degenerate outer retinal layers resulting in a retinopexy that is known to make subretinal gene therapy particularly challenging in these patients.

CONCLUSION

Although retinal gene therapy is commonly targeted to the macular area in choroideremia, the observation of a rhegmatogenous retinal detachment indicates that the peripheral retina may not fuse with the residual choroid as occurs in the equatorial and macular regions. If this hypothesis is correct, targeting gene therapy to the retinal periphery even in advanced cases may be feasible and could potentially be used to preserve navigational vision.

Clinical Perspectives and Trends: Microperimetry as a trial endpoint in retinal disease

Endpoint development trials are underway across the spectrum of retinal disease. New validated endpoints are urgently required for the assessment of emerging gene therapies and in preparation for the arrival of novel therapeutics targeting early stages of common sight-threatening conditions such as age-related macular degeneration. Visual function measures are likely to be key candidates in this search. Over the last two decades, microperimetry has been used extensively to characterize functional vision in a wide range of retinal conditions, detecting subtle defects in retinal sensitivity that precede visual acuity loss and tracking disease progression over relatively short periods. Given these appealing features, microperimetry has already been adopted as an endpoint in interventional studies, including multicenter trials, on a modest scale. A review of its use to date shows a concurrent lack of consensus in test strategy and a wealth of innovative disease and treatment-specific metrics which may show promise as clinical trial endpoints. There are practical issues to consider, but these have not held back its popularity and it remains a widely used psychophysical test in research. Endpoint development trials will undoubtedly be key in understanding the validity of microperimetry as a clinical trial endpoint, but existing signs are promising.

The Michigan Retinal Degeneration Questionnaire: A Patient-Reported Outcome Instrument for Inherited Retinal Degenerations

PURPOSE

To create a psychometrically validated patient-reported outcome measure for inherited retinal degenerations.

DESIGN

Qualitative and quantitative patient-reported outcome (PROs) questionnaire development using item response theory validation.

METHODS

One hundred twenty-eight patients with a diagnosis of an inherited retinal degeneration at the Kellogg Eye Center (University of Michigan) were recruited and administered a 166-item questionnaire comprising 7 expert-defined domains. The questionnaire was re-administered 4-16 days later to a subset of 25 participants to assess test-retest variability. Graded response models were fit by Cai's Metropolis-Hastings Robbins-Monro algorithm using the R (version 3.6.3) package mirt. Model data were fit to assess questionnaire dimensionality, to estimate item information, and to score participants. Poorly functioning items were removed, and the model was refit to create the final questionnaire.

RESULTS

The psychometrically validated PROs measure was reduced to a 59-item questionnaire measuring 7 unidimesnional domains: central vision, color vision, contrast sensitivity, scotopic function, photopic peripheral vision, mesopic peripheral vision, and photosensitivity. A total of 39 items were removed because of poor factor loading, low item information, poor person-ability differentiation, or high item-level interdependence. This novel questionnaire produces a reliable domain score for person ability that does not show significant test-retest variability across repeated administration.

CONCLUSIONS

The final PRO questionnaire, known as the Michigan Retinal Degeneration Questionnaire, is psychometrically validated and available for use in the evaluation of patients with inherited retinal degenerations.

Update on Gene Therapy Clinical Trials for Choroideremia and Potential Experimental Therapies

Background and objectives: Choroideremia (CHM) is an X-linked recessive chorioretinal dystrophy caused by mutations involving the CHM gene. Gene therapy has entered late-phase clinical trials, although there have been variable results. This review gives a summary on the outcomes of phase I/II CHM gene therapy trials and describes other potential experimental therapies. Materials and Methods: A Medline (National Library of Medicine, Bethesda, MD, USA) search was performed to identify all articles describing gene therapy treatments available for CHM. Results: Five phase I/II clinical trials that reported subretinal injection of adeno-associated virus Rab escort protein 1 (AAV2.REP1) vector in CHM patients were included. The Oxford study (NCT01461213) included 14 patients; a median gain of 5.5 ± 6.8 SD (-6 min, 18 max) early treatment diabetic retinopathy study (ETDRS) letters was reported. The Tubingen study (NCT02671539) included six patients; only one patient had an improvement of 17 ETDRS letters. The Alberta study (NCT02077361) enrolled six patients, and it reported a minimal vision change, except for one patient who gained 15 ETDRS letters. Six patients were enrolled in the Miami trial (NCT02553135), which reported a median gain of 2 ± 4 SD (-1 min, 10 max) ETDRS letters. The Philadelphia study (NCT02341807) included 10 patients; best corrected visual acuity (BCVA) returned to baseline in all by one-year follow-up, but one patient had -17 ETDRS letters from baseline. Overall, 40 patients were enrolled in trials, and 34 had 2 years of follow-up, with a median gain of 1.5 ± 7.2 SD (-14 min, 18 max) in ETDRS letters. Conclusions: The primary endpoint, BCVA following gene therapy in CHM, showed a marginal improvement with variability between trials. Optimizing surgical technique and pre-, peri-, and post-operative management with immunosuppressants to minimize any adverse ocular inflammatory events could lead to reduced incidence of complications. The ideal therapeutic window needs to be addressed to ensure that the necessary cell types are adequately transduced, minimizing viral toxicity, to prolong long-term transgenic potential. Long-term efficacy will be addressed by ongoing studies.

Gene Therapy for Progressive Familial Intrahepatic Cholestasis: Current Progress and Future Prospects

Progressive Familial Intrahepatic Cholestasis (PFIC) are inherited severe liver disorders presenting early in life, with high serum bile salt and bilirubin levels. Six types have been reported, two of these are caused by deficiency of an ABC transporter; ABCB11 (bile salt export pump) in type 2; ABCB4 (phosphatidylcholine floppase) in type 3. In addition, ABCB11 function is affected in 3 other types of PFIC. A lack of effective treatment makes a liver transplantation necessary in most patients. In view of long-term adverse effects, for instance due to life-long immune suppression needed to prevent organ rejection, gene therapy could be a preferable approach, as supported by proof of concept in animal models for PFIC3. This review discusses the feasibility of gene therapy as an alternative for liver transplantation for all forms of PFIC based on their pathological mechanism. Conclusion: Using presently available gene therapy vectors, major hurdles need to be overcome to make gene therapy for all types of PFIC a reality.

Treatment-Emergent Adverse Events in Gene Therapy Trials for Inherited Retinal Diseases: A Narrative Review

Patient safety is a primary priority in the conduction of retinal gene therapy trials. An understanding of risk factors and mitigation strategies for post-procedure complications is crucial for the optimization of gene therapy clinical trial protocols. In this review, we synthesize the literature on ocular delivery methods, vector platforms, and treatment-emergent adverse effects in recent gene therapy clinical trials for inherited retinal diseases.

Genetic defects of CHM and visual acuity outcome in 24 choroideremia patients from 16 Japanese families

Choroideremia (CHM) is an incurable progressive chorioretinal dystrophy. Little is known about the natural disease course of visual acuity in the Japanese population. We aimed to investigate the genetic spectrum of the CHM gene and visual acuity outcomes in 24 CHM patients from 16 Japanese families. We measured decimal best-corrected visual acuity (BCVA) at presentation and follow-up, converted to logMAR units for statistical analysis. Sanger and/or whole-exome sequencing were performed to identify pathogenic CHM variants/deletions. The median age at presentation was 37.0 years (range, 5–76 years). The mean follow-up interval was 8.2 years. BCVA of the better-seeing eye at presentation was significantly worsened with increasing age (r = 0.515, p < 0.01), with a high rate of BCVA decline in patients > 40 years old. A Kaplan–Meier survival curve suggested that a BCVA of Snellen equivalent 20/40 at follow-up remains until the fifties. Fourteen pathogenic variants, 6 of which were novel [c.49 + 5G > A, c.116 + 5G > A, p.(Gly176Glu, Glu177Ter), p.Tyr531Ter, an exon 2 deletion, and a 5.0-Mb deletion], were identified in 15 families. No variant was found in one family only. Our BCVA outcome data are useful for predicting visual prognosis and determining the timing of intervention in Japanese patients with CHM variants.

Edge of Scotoma Sensitivity as a Microperimetry Clinical Trial End Point in USH2A Retinopathy

Purpose

Microperimetry is commonly used to assess retinal function. We perform cross-sectional and longitudinal analysis on microperimetry parameters in USH2A retinopathy and explore end points suitable for future clinical trials.

Methods

Microperimetry was performed using two grids, Grid 1 (18° diameter) and Grid 2 (6° diameter). In Grid 1, four parameters (number of nonscotomatous loci, mean sensitivity [MS], responding point sensitivity [RPS], and edge of scotoma sensitivity [ESS]) were analyzed. In Grid 2, number of nonscotomatous loci and MS were examined. Interocular symmetry was also examined. Longitudinal analysis was conducted in a subset of eyes.

Results

Microperimetry could be performed in 16 of 21 patients. In Grid 1 (n = 15; average age, 35.6 years), average number of nonscotomatous loci, MS, RPS, and ESS were 46.6 loci, 10.0 dB, 14.7 and 9.6 dB, respectively. In Grid 2 (n = 13; average age, 37.4 years), 12 eyes had measurable sensitivity across the entire grid. Average MS was 23.8 dB. Interocular analysis revealed large 95% confidence intervals for all parameters. Longitudinally, Grid 1 (n = 12, average follow-up 2.6 years) ESS showed the fastest rate of decline (–1.84 dB/y) compared with MS (–0.34 dB/y) and RPS (–0.90 dB/y).

Conclusions

Our data suggest that ESS may be more useful than MS and RPS in test grids that cover a large extent of the macula. We caution the use of contralateral eye as an internal control.

Translational Relevance

ESS may decrease the duration or sample size of treatment trials in USH2A retinopathy.

The new landscape of retinal gene therapy

Novel therapeutics for inherited retinal dystrophies (IRDs) have rapidly evolved since groundbreaking clinical trials for LCA due to RPE65 mutations led to the first FDA-approved in vivo gene therapy. Since then, advancements in viral vectors have led to more efficient AAV transduction and developed other viral vectors for gene augmentation therapy of large gene targets. Furthermore, significant developments in gene editing and RNA modulation technologies have introduced novel capabilities for treatment of autosomal dominant diseases, intronic mutations, and/or large genes otherwise unable to be treated with current viral vectors. We highlight strategies currently being evaluated in gene therapy clinical trials and promising preclinical developments for IRDs.

The X-linked retinopathies: Physiological insights, pathogenic mechanisms, phenotypic features and novel therapies

X-linked retinopathies represent a significant proportion of monogenic retinal disease. They include progressive and stationary conditions, with and without syndromic features. Many are X-linked recessive, but several exhibit a phenotype in female carriers, which can help establish diagnosis and yield insights into disease mechanisms. The presence of affected carriers can misleadingly suggest autosomal dominant inheritance. Some disorders (such as RPGR-associated retinopathy) show diverse phenotypes from variants in the same gene and also highlight limitations of current genetic sequencing methods. X-linked disease frequently arises from loss of function, implying potential for benefit from gene replacement strategies. We review X-inactivation and X-linked inheritance, and explore burden of disease attributable to X-linked genes in our clinically and genetically characterised retinal disease cohort, finding correlation between gene transcript length and numbers of families. We list relevant genes and discuss key clinical features, disease mechanisms, carrier phenotypes and novel experimental therapies. We consider in detail the following: RPGR (associated with retinitis pigmentosa, cone and cone-rod dystrophy), RP2 (retinitis pigmentosa), CHM (choroideremia), RS1 (X-linked retinoschisis), NYX (complete congenital stationary night blindness (CSNB)), CACNA1F (incomplete CSNB), OPN1LW/OPN1MW (blue cone monochromacy, Bornholm eye disease, cone dystrophy), GPR143 (ocular albinism), COL4A5 (Alport syndrome), and NDP (Norrie disease and X-linked familial exudative vitreoretinopathy (FEVR)). We use a recently published transcriptome analysis to explore expression by cell-type and discuss insights from electrophysiology. In the final section, we present an algorithm for genes to consider in diagnosing males with non-syndromic X-linked retinopathy, summarise current experimental therapeutic approaches, and consider questions for future research.

Human iPSC Modeling Reveals Mutation-Specific Responses to Gene Therapy in a Genotypically Diverse Dominant Maculopathy

Dominantly inherited disorders are not typically considered to be therapeutic candidates for gene augmentation. Here, we utilized induced pluripotent stem cell-derived retinal pigment epithelium (iPSC-RPE) to test the potential of gene augmentation to treat Best disease, a dominant macular dystrophy caused by over 200 missense mutations in BEST1. Gene augmentation in iPSC-RPE fully restored BEST1 calcium-activated chloride channel activity and improved rhodopsin degradation in an iPSC-RPE model of recessive bestrophinopathy as well as in two models of dominant Best disease caused by different mutations in regions encoding ion-binding domains. A third dominant Best disease iPSC-RPE model did not respond to gene augmentation, but showed normalization of BEST1 channel activity following CRISPR-Cas9 editing of the mutant allele. We then subjected all three dominant Best disease iPSC-RPE models to gene editing, which produced premature stop codons specifically within the mutant BEST1 alleles. Single-cell profiling demonstrated no adverse perturbation of retinal pigment epithelium (RPE) transcriptional programs in any model, although off-target analysis detected a silent genomic alteration in one model. These results suggest that gene augmentation is a viable first-line approach for some individuals with dominant Best disease and that non-responders are candidates for alternate approaches such as gene editing. However, testing gene editing strategies for on-target efficiency and off-target events using personalized iPSC-RPE model systems is warranted. In summary, personalized iPSC-RPE models can be used to select among a growing list of gene therapy options to maximize safety and efficacy while minimizing time and cost. Similar scenarios likely exist for other genotypically diverse channelopathies, expanding the therapeutic landscape for affected individuals.

Gene Therapy Preserves Retinal Structure and Function in a Mouse Model of NMNAT1-Associated Retinal Degeneration

No treatment is available for nicotinamide mononucleotide adenylyltransferase 1 (NMNAT1)-associated retinal degeneration, an inherited disease that leads to severe vision loss early in life. Although the causative gene, NMNAT1, plays an essential role in nuclear nicotinamide adenine dinucleotide (NAD)⁺ metabolism in tissues throughout the body, NMNAT1-associated disease is isolated to the retina. Since this condition is recessive, supplementing the retina with a normal copy of NMNAT1 should protect vulnerable cells from disease progression. We tested this hypothesis in a mouse model that harbors the p.Val9Met mutation in Nmnat1 and consequently develops a retinal degenerative phenotype that recapitulates key features of the human disease. Gene augmentation therapy, delivered by subretinal injection of adeno-associated virus (AAV) carrying a normal human copy of NMNAT1, rescued retinal structure and function. Due to the early-onset profile of the phenotype, a rapidly activating self-complementary AAV was required to initiate transgene expression during the narrow therapeutic window. These data represent the first proof of concept for a therapy to treat patients with NMNAT1-associated disease.

Progress in treating inherited retinal diseases: Early subretinal gene therapy clinical trials and candidates for future initiatives

Due to improved phenotyping and genetic characterization, the field of 'incurable' and 'blinding' inherited retinal diseases (IRDs) has moved substantially forward. Decades of ascertainment of IRD patient data from Philadelphia and Toronto centers illustrate the progress from Mendelian genetic types to molecular diagnoses. Molecular genetics have been used not only to clarify diagnoses and to direct counseling but also to enable the first clinical trials of gene-based treatment in these diseases. An overview of the recent reports of gene augmentation clinical trials by subretinal injections is used to reflect on the reasons why there has been limited success in this early venture into therapy. These first-in human experiences have taught that there is a need for advancing the techniques of delivery of the gene products - not only for refining further subretinal trials, but also for evaluating intravitreal delivery. Candidate IRDs for intravitreal gene delivery are then suggested to illustrate some of the disorders that may be amenable to improvement of remaining central vision with the least photoreceptor trauma. A more detailed understanding of the human IRDs to be considered for therapy and the calculated potential for efficacy should be among the routine prerequisites for initiating a clinical trial.

Content generation for patient-reported outcome measures for retinal degeneration therapeutic trials

PURPOSE

Generate content for a patient-reported outcome (PRO) measure for use in future clinical trials for inherited retinal degenerations.

METHODS

Patients at the University of Michigan Kellogg Eye Center with a clinical diagnosis of inherited retinal degeneration with varying phenotypes were recruited for interviews. First, in-depth interviews were performed to solicit a wide range of patient experiences pertaining to visual function. Coders qualitatively analyzed the transcripts from these interviews using Atlas.ti software (Version 8.1.3 (522)) to draft questionnaire items. Next, the questionnaire was tested and refined based on participant feedback in cognitive interviews and administrator feedback in the pilot survey administration (pilot interviews).

RESULTS

A total of 55 participants with a clinical diagnosis of inherited retinal degeneration were interviewed throughout the three study phases: in-depth interviews (n = 26), cognitive interviews (n = 16), and pilot interviews (n = 13). Coded items were analyzed for frequency of occurrence and related themes, then organized into common domains. Within each domain, PRO items were drafted to address the functional limitations or adaptations experienced by patients.

CONCLUSIONS

Items for a PRO measure have been drafted and evaluated for interpretability in the target inherited retinal degeneration patient population. Content validity for the items was established through a process of in-depth interviews, cognitive interviews, and pilot interviews.

Interpreting MAIA Microperimetry Using Age- and Retinal Loci-Specific Reference Thresholds

Purpose

Macular Integrity Assessment (MAIA) microperimetry is used widely in clinical trials and routine practice to assess paracentral scotoma. Current interpretation of MAIA is based on an assumed uniform 25 decibel (dB) cutoff for normal function irrespective of subject age and retinal location. We examined this convention by establishing an age- and loci-specific reference in healthy eyes and comparing this to the <25 dB cutoff.

Methods

Retrospective MAIA results from healthy eyes were analyzed for prevalence of loci with <25 dB. At each locus, a new reference cutoff was derived from quantile regression of sensitivity against age at the 2.5th percentile. Two clinical cases of serial MAIA testing were analyzed using the new approach and compared to the <25 dB cutoff.

Results

Fifty-four and 56 age-matched (range: 16–75 years) healthy eyes underwent small (37 loci) and large (68 loci) grid testing, respectively. Retinal sensitivity <25 dB was found in 5% of the small grid (1998 data points) and 10% of the large grid (3808 data points). These were found predominantly in older subjects and at the central point or in the perifoveal region. Quantile regression at each individual locus showed age-related decline with a median gradient of 0.6 dB/decade.

Conclusions

We caution against using <25 dB cutoff in MAIA interpretation and advocate an age- and loci-specific cutoff criterion.

Translational Relevance

Our study suggests that MAIA interpretation is influenced by the criterion used for defining abnormal pointwise measurement.

Quantification of RPE Changes in Choroideremia Using a Photoshop-Based Method

Purpose

To develop a reliable and efficient method for quantifying the area of preserved retinal pigment epithelium (RPE), facilitating the evaluation of disease progression or response to therapy in choroideremia (CHM).

Methods

The fundus autofluorescence images of CHM patients were captured at baseline and 1 year. A Photoshop-based method was developed to allow the reliable measurement of the RPE area. The results were compared with measurements generated by the Heidelberg Eye Explorer 2 (HEYEX2). The areas measured by two independent graders were compared to assess the test-retest reliability.

Results

By using the Photoshop-based method, the area of the RPE measured from 64 eyes was seen to decrease significantly (P < 0.001) at a rate of 2.57 ± 3.22 mm² annually, and a percentage of 8.39% ± 5.24%. The average standard deviations for Photoshop were less than that for HEYEX2 (0.5-1.1 in grader 1; 0.4-1.6 in grader 2), indicating less intragrader variability. The RPE decrease as determined by the Photoshop-based method showed excellent reliability with an intraclass correlation coefficient of 0.944 (95% confidence interval, 0.907-0.966). In Bland-Altman plots, the Photoshop method also exhibited better intergrader agreement.

Conclusions

Photoshop-based quantification of preserved RPE area in patients with CHM is feasible and has better test-retest reliability compared with the HEYEX2 method.

Translational Relevance

An accurate quantification method for longitudinal RPE change in CHM patients is an important tool for the evaluation of efficacy in any therapeutic trials.

Recombinant Adeno-Associated Viral Vectors (rAAV)-Vector Elements in Ocular Gene Therapy Clinical Trials and Transgene Expression and Bioactivity Assays

Inherited retinal dystrophies and optic neuropathies cause chronic disabling loss of visual function. The development of recombinant adeno-associated viral vectors (rAAV) gene therapies in all disease fields have been promising, but the translation to the clinic has been slow. The safety and efficacy profiles of rAAV are linked to the dose of applied vectors. DNA changes in the rAAV gene cassette affect potency, the expression pattern (cell-specificity), and the production yield. Here, we present a library of rAAV vectors and elements that provide a workflow to design novel vectors. We first performed a meta-analysis on recombinant rAAV elements in clinical trials (2007-2020) for ocular gene therapies. We analyzed 33 unique rAAV gene cassettes used in 57 ocular clinical trials. The rAAV gene therapy vectors used six unique capsid variants, 16 different promoters, and six unique polyadenylation sequences. Further, we compiled a list of promoters, enhancers, and other sequences used in current rAAV gene cassettes in preclinical studies. Then, we give an update on pro-viral plasmid backbones used to produce the gene therapy vectors, inverted terminal repeats, production yield, and rAAV safety considerations. Finally, we assess rAAV transgene and bioactivity assays applied to cells or organoids in vitro, explants ex vivo, and clinical studies.

Peripapillary Intravitreal Injection Improves AAV-Mediated Retinal Transduction

The intravitreal (IVT) injection method is a choice when targeting the inner retina for gene therapy. However, the transduction efficiency of adeno-associated virus (AAV) vectors administered by the IVT route is usually low and may be affected by several factors. To improve the transduction efficiency, we developed a novel illuminated long-needle attached injection system and injected AAV2-CMV (cytomegalovirus)-EGFP in front of the retina in rabbit eyes. Ophthalmological examinations were performed and the levels of pro-inflammatory cytokines in the aqueous humor were assessed at the baseline and 1 month, and the results were compared with those of the conventional injection method. Retinal tissues were used for immunohistochemistry. In the ophthalmological examinations, no significant inflammatory signs were detected in both groups, except for transient, mild hyperemia. In the tissues of the rabbits in the peripapillary injection group, significantly increased GFP expression was detected at the ganglion cell and the inner nuclear layers (p < 0.01). There were no differences between groups in glial activation and expressions of interleukin (IL)-6 and IL-8. These results suggest that peripapillary IVT injection in front of the retina would be safe and efficiently transduce viral vectors into the retina of large animals and is considered as a potential method for use in clinical trials.

What Is the Impact of Intraoperative Microscope-Integrated OCT in Ophthalmic Surgery? Relevant Applications and Outcomes. A Systematic Review

Background: Optical coherence tomography (OCT) has recently been introduced in the operating theatre. The aim of this review is to present the actual role of microscope-integrated optical coherence tomography (MI-OCT) in ophthalmology. Method: A total of 314 studies were identified, following a literature search adhering to the preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines. After full-text evaluation, 81 studies discussing MI-OCT applications in ophthalmology were included. Results: At present, three microscope-integrated optical coherence tomography systems are commercially available. MI-OCT can help anterior and posterior segment surgeons in the decision-making process, providing direct visualization of anatomic planes before and after surgical manoeuvres, assisting in complex cases, and detecting or confirming intraoperative complications. Applications range from corneal transplant to macular surgery, including cataract surgery, glaucoma surgery, paediatric examination, proliferative diabetic retinopathy surgery, and retinal detachment surgery. Conclusion: The use of MI-OCT in ophthalmic surgery is becoming increasingly prevalent and has been applied in almost all procedures. However, there are still limitations to be overcome and the technology involved remains difficult to access and use.

Next-generation sequencing-based clinical diagnosis of choroideremia and comprehensive mutational and clinical analyses

Background

To report the clinical and genetic findings from seven Chinese patients with choroideremia.

Methods

Five hundred seventy-eight patients with a clinically suspected diagnosis of retinitis pigmentosa (RP) underwent comprehensive ophthalmic examinations. Next-generation sequencing (NGS) was performed on samples from all patients. Detailed clinical characteristics of the patients with choroideremia identified in this study were assessed using multimodal imaging.

Results

Seven patients with choroideremia were identified, and six novel variants in CHM (c.1960 T > C p.Ter654Gln, c.1257del p.Ile420*fs1, c.1103_1121delATGGCAACACTCCATTTTT p.Tyr368Cysfs35, c.1414-2A > T, and c.1213C > T p.Gln405Ter, c.117-1G > A) were revealed. All variants were deleterious mutations: two were frameshifts, two were nonsense mutations, two were splicing mutations, and one was a readthrough mutation. The clinical phenotypes of these patients were markedly heterogeneous, and they shared many common clinical features with RP, including night blindness, constriction of the visual field and gradually reduced visual acuity. However, patients with choroideremia showed pigment hypertrophy and clumping, and chorioretinal atrophy, and a majority of patients with choroideremia presented with retinal tubulations in the outer layer of the retina.

Conclusions

We provide a detailed description of the genotypes and phenotypes of seven patients with choroideremia who were accurately diagnosed using NGS. These findings provide a better understanding of the genetics and phenotypes of choroideremia.

Long-term natural history of visual acuity in eyes with choroideremia: a systematic review and meta-analysis of data from 1004 individual eyes

BACKGROUND/AIMS

Best-corrected visual acuity (BCVA) is the most common primary endpoint in treatment trials for choroideremia (CHM) but the long-term natural history of BCVA is unclear.

METHODS

We searched in seven databases to identify studies that reported BCVA of untreated eyes with CHM. We sought individual-level data and performed segmented regression between BCVA and age. For eyes followed longitudinally, we introduced a horizontal translation factor to each dataset to account for different ages at onset of a rapid BCVA decline.

RESULTS

We included 1004 eyes from 23 studies. BCVA of the right and left eyes was moderately correlated (r=0.60). BCVA as a function of age followed a 2-phase decline (slow followed by rapid decline), with an estimated transition age of 39.1 years (95% CI 33.5 to 44.7). After the introduction of horizontal translation factors to longitudinal datasets, BCVA followed a 2-phase decline until it reached 0 letters (r²=0.90). The BCVA decline rate was 0.33 letters/year (95% CI -0.38 to 1.05) before 39 years, and 1.23 letters/year (95% CI 0.55 to 1.92) after 39 years (p=0.004).

CONCLUSION

BCVA in eyes with CHM follows a 2-phase linear decline with a transition age of approximately 39 years. Future trials enrolling young patients may not be able to use BCVA as a primary or sole endpoint, but rather, may need to employ additional disease biomarkers that change before age 39. BCVA may still have utility as a primary endpoint for patients older than 39 years who have measurable BCVA decline rates.

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.

Synonymous Variant in the CHM Gene Causes Aberrant Splicing in Choroideremia

Purpose

Choroideremia is an inherited retinal degeneration caused by 280 different pathogenic variants in the CHM gene. Only one silent/synonymous variant (c.1359C>T; p.(Ser453=)) has been reported and was classified as inconclusive based on in silico analysis. This study elucidates the pathogenicity of this variant also found in a Brazilian patient.

Methods

Ophthalmological examinations such as color fundus photography, spectral-domain optical coherence tomography, fundus autofluorescence, and macular integrity assessment microperimetry were performed. The subjects' total RNA was extracted from peripheral blood cells. cDNA was synthesized and the amplification between exon 10 and 14 of the CHM mRNA was performed. The amplification products were sequenced by Sanger sequencing and the results were aligned to the reference sequence.

Results

The synonymous variant c.1359C>T p.(Ser453=) in the CHM gene is associated with an error in mRNA processing, leading preferentially to production of an aberrant transcript without exon 11 (p.(Gln451Phefs*3)). This anomalous mRNA production is related to typical choroideremia phenotype.

Conclusions

These molecular findings reinforce the need for more detailed investigation of silent variants in patients with well-defined phenotype of retinal dystrophies. Molecular and clinical findings provided evidence that c.1359C>T (p.(Gln451Phefs*3)) in CHM should be considered a disease-causing variant.

Long-term Natural History of Atrophy in Eyes with Choroideremia-A Systematic Review and Meta-analysis of Individual-Level Data

PURPOSE

To conduct a systematic review and meta-analysis of the natural history of atrophy secondary to choroideremia (CHM).

CLINICAL RELEVANCE

A sensitive and reliable anatomic measure to monitor disease progression is needed in treatment trials for CHM. However, the long-term natural history of the residual retinal pigment epithelium (RPE) is unclear, with reported RPE area decline rates varying widely among patients.

METHODS

We searched in 7 literature databases up through July 17, 2019, to identify studies that assessed the residual RPE area in untreated eyes with CHM using fundus autofluorescence (FAF). We sought individual-eye data and investigated the RPE decline pattern using 3 models: the area linear model (ALM), radius linear model (RLM), and area exponential model (AEM), in which the area, radius, and log-transformed area of RPE change linearly with time, respectively. To account for different eyes' entry times into the studies, we added a horizontal translation factor to each dataset. The RPE decline rate was estimated using a 2-stage random-effects meta-analysis. We assessed the risk of bias using the Quality In Prognosis Studies tool.

RESULTS

Of 807 articles screened, we included 9 articles containing cross-sectional data (257 eyes) from 6 studies and longitudinal data (229 visits from 68 eyes) from 5 studies. The residual RPE area followed a trend of exponential decay as a function of patient age. After the introduction of horizontal translation factors to longitudinal datasets of individual eyes, the datasets fit along a straight line in the AEM over nearly 60 years (r² = 0.997). The decline rate of log-transformed RPE area was 0.050 (95% confidence interval, 0.046-0.055) log(mm²)/year and was independent of the baseline RPE area (r = -0.18; P = 0.15) and age (r = 0.06; P = 0.63). In contrast, the decline rates of the area and effective radius of residual RPE strongly correlated with the baseline RPE area (r = 0.90 and 0.61, respectively; P < 0.001).

CONCLUSIONS

The loss of residual RPE area in untreated eyes with CHM follows the AEM over approximately 60 years. Log-transformed residual RPE area measured by FAF can serve as an anatomic endpoint to monitor CHM.