Correlation of Optical Coherence Tomography and Autofluorescence in the Outer Retina and Choroid of Patients With Choroideremia

Optical coherence tomography in children with inherited retinal disease

Recent advances have led to therapeutic options becoming available for people with inherited retinal disease. In particular, gene therapy has been shown to hold great promise for slowing vision loss from inherited retinal disease. Recent studies suggest that gene therapy is likely to be most effective when implemented early in the disease process, making consideration of paediatric populations important. It is therefore necessary to have a comprehensive understanding of retinal imaging in children with inherited retinal diseases, in order to monitor disease progression and to determine which early retinal biomarkers may be used as outcome measures in future clinical trials. In addition, as many optometrists will review children with an inherited retinal disease, an understanding of the expected imaging outcomes can improve clinical care. This review focuses on the most common imaging modality used in research assessment of paediatric inherited retinal diseases: optical coherence tomography. Optical coherence tomography findings can be used in both the clinical and research setting. In particular, the review discusses current knowledge of optical coherence tomography findings in eight paediatric inherited retinal diseases - Stargardt disease, Bests disease, Leber's congenital amaurosis, choroideremia, RPGR related retinitis pigmentosa, Usher syndrome, X-linked retinoschisis and, Batten disease.

Loss of REP1 impacts choroidal melanogenesis and vasculogenesis in choroideremia

Choroideremia (CHM) is a rare X-linked chorioretinal dystrophy affecting the photoreceptors, retinal pigment epithelium (RPE) and choroid, however, the involvement of the choroid in disease progression is not fully understood. CHM is caused by mutations in the CHM gene, encoding the ubiquitously expressed Rab escort protein 1 (REP1). REP1 plays an important role in intracellular trafficking of vesicles, including melanosomes. In this study, we examined the ultrastructure of the choroid in chmru848 fish and Chmnull/WT mouse models using transmission electron and confocal microscopy. Significant pigmentary disruptions were observed, with lack of melanosomes in the choroid of chmru848 fish from 4 days post fertilisation (4dpf), and a reduction in choroidal blood vessel diameter and interstitial pillars suggesting a defect in vasculogenesis. Total melanin and expression of melanogenesis genes tyr, tryp1a, mitf, dct and pmel were also reduced from 4dpf. In Chmnull/WT mice, choroidal melanosomes were significantly smaller at 1 month, with reduced eumelanin at 1 year. The choroid in CHM patients were also examined using spectral domain optical coherence tomography (SD-OCT) and OCT-angiography (OCT-A) and the area of preserved choriocapillaris (CC) was found to be smaller than that of overlying photoreceptors, suggesting that the choroid is degenerating at a faster rate. Histopathology of an enucleated eye from a 74-year-old CHM male patient revealed isolated areas of RPE but no associated underlying CC. Pigmentary disruptions in CHM animal models reveal an important role for REP1 in melanogenesis, and drugs that improve melanin production represent a potential novel therapeutic avenue.

Choroideremia: The Endpoint Endgame

Choroideremia is an X-linked retinal degeneration resulting from the progressive, centripetal loss of photoreceptors and choriocapillaris, secondary to the degeneration of the retinal pigment epithelium. Affected individuals present in late childhood or early teenage years with nyctalopia and progressive peripheral visual loss. Typically, by the fourth decade, the macula and fovea also degenerate, resulting in advanced sight loss. Currently, there are no approved treatments for this condition. Gene therapy offers the most promising therapeutic modality for halting or regressing functional loss. The aims of the current review are to highlight the lessons learnt from clinical trials in choroideremia, review endpoints, and propose a future strategy for clinical trials.

Clinical and Genetic Findings in Korean Patients with Choroideremia

PURPOSE

We share and analyze the clinical presentations and genotypes of Korean male patients and female carriers who visited our clinic.

METHODS

Six male patients and three female carriers with comprehensive ophthalmic examinations and next-generation sequencing were included. Detailed clinical features were identified using visual field (VF) test and multimodal imaging including color fundus photography, fundus autofluorescence (FAF), and optical coherence tomography (OCT).

RESULTS

Six male patients were diagnosed with choroideremia at the median age of 25 years. Before genetic testing, three patients (50.0%) were clinically diagnosed with choroideremia, while the other three patients (50.0%) with retinitis pigmentosa. Patients showed different types of hemizygous CHM variants, including two nonsense variants, c.715C>T:p.(Arg239*) and c.799C>T:p.(Arg267*); two frameshift variants, c.1584_1587del:p.(Val529Hisfs*7) and c.403_404del:p.(Asp135Phefs*9); one splicing variant c.1511-28_1511-2del; and one exon 2-8 duplication. The latter three variants were novel. Two female carriers had heterozygous exon 2-8 duplication and the other one female carrier had heterozygous nonsense variant c.715C>T:p. (Arg239*). Fundus showed diffuse yellow-whitish scleral reflex and granular pigmented lesions. FAF showed multiple patchy hypofluorescence lesions, sparing macula. OCT showed thinning of outer nuclear layer, ellipsoid zone, retinal pigment epithelium layer, choroid thickness, interlaminar bridges, outer retinal tubulations, and microcysts in the inner nuclear layer. VF showed ring scotoma pattern with small amount of remaining central field. Asymptomatic female carriers showed variable fundus findings and mild changes in OCT.

CONCLUSIONS

A detailed description of the genotypes with three novel mutations and phenotypes of six choroideremia patients and three CHM mutation female carriers are presented.

Choroideremia: Toward Regulatory Approval of Retinal Gene Therapy

Choroideremia is an X-linked inherited retinal degeneration characterized by primary centripetal degeneration of the retinal pigment epithelium (RPE), with secondary degeneration of the choroid and retina. Affected individuals experience reduced night vision in early adulthood with blindness in late middle age. The underlying CHM gene encodes REP1, a protein involved in the prenylation of Rab GTPases essential for intracellular vesicle trafficking. Adeno-associated viral gene therapy has demonstrated some benefit in clinical trials for choroideremia. However, challenges remain in gaining regulatory approval. Choroideremia is slowly progressive, which presents difficulties in demonstrating benefit over short pivotal clinical trials that usually run for 1-2 years. Improvements in visual acuity are particularly challenging due to the initial negative effects of surgical detachment of the fovea. Despite these challenges, great progress toward a treatment has been made since choroideremia was first described in 1872.

Retinitis Pigmentosa: Current Clinical Management and Emerging Therapies

Retinitis pigmentosa (RP) comprises a group of inherited retinal dystrophies characterized by the degeneration of rod photoreceptors, followed by the degeneration of cone photoreceptors. As a result of photoreceptor degeneration, affected individuals experience gradual loss of visual function, with primary symptoms of progressive nyctalopia, constricted visual fields and, ultimately, central vision loss. The onset, severity and clinical course of RP shows great variability and unpredictability, with most patients already experiencing some degree of visual disability in childhood. While RP is currently untreatable for the majority of patients, significant efforts have been made in the development of genetic therapies, which offer new hope for treatment for patients affected by inherited retinal dystrophies. In this exciting era of emerging gene therapies, it remains imperative to continue supporting patients with RP using all available options to manage their condition. Patients with RP experience a wide variety of physical, mental and social-emotional difficulties during their lifetime, of which some require timely intervention. This review aims to familiarize readers with clinical management options that are currently available for patients with RP.

Outer retinal tubulation in Bietti crystalline dystrophy associated with the retinal pigment epithelium atrophy

PURPOSE

To determine the prognostic value of outer retinal tubulation (ORT) in the eyes of a Chinese cohort with Bietti crystalline dystrophy (BCD).

METHODS

This retrospective, multicenter cohort study enrolled forty-two patients with clinically and genetically diagnosed BCD. Eighty eyes with good-quality images of spectral domain optical coherence tomography (SD-OCT) were included. Demographic details and clinical data were collected. The characteristics of ORT, including prevalence, location and morphologic characteristics were analyzed.

RESULTS

Forty-two BCD patients harbored potentially CYP4V2 disease-causing mutations. The mutation spectrum comprised 17 unique variants, nine of which were novel. Fifty-two of these 80 eyes demonstrated evidence of ORT. The incidence of ORT is significantly higher in stage 2 than other stages (P<0.001). ORT was mainly bilateral and located at margin of the atrophic area of retinal pigmental epithelial (RPE), and dynamically changed with the progressive RPE atrophy. The process of RPE atrophy was slower in eyes with ORT (P=0.017), with significantly longer intact RPE width in stage 3 (P=0.024). Eyes with ORT had slower vision loss than eyes without ORT (P=0.044).

CONCLUSION

ORT may be a sign of the onset of RPE atrophy in early-stage BCD and may suggest less risk of rapid progression in late-stage BCD.

AAV2-hCHM Subretinal Delivery to the Macula in Choroideremia: Two Year Interim Results of an Ongoing Phase I/II Gene Therapy Trial

PURPOSE

To assess the safety of the subretinal delivery of a recombinant adeno-associated virus serotype 2 (AAV2) vector carrying a human CHM-encoding cDNA in choroideremia (CHM).

DESIGN

Prospective, open-label, non-randomized, dose-escalation, phase 1/2 clinical trial.

SUBJECTS, PARTICIPANTS, AND/OR CONTROLS

Fifteen CHM patients (ages 20-57 years at dosing).

METHODS, INTERVENTION, OR TESTING

Patients received uniocular subfoveal injections of low dose (up to 5x10¹⁰ vector genome (vg) per eye, n=5) or high dose (up to 1x10¹¹ vg per eye, n=10) AAV2-hCHM. Patients were evaluated pre- and post-operatively for two years with ophthalmic examinations, multimodal retinal imaging and psychophysical testing.

MAIN OUTCOME

Measures: visual acuity (VA), perimetry (10-2 protocol), spectral-domain optical coherence tomography (SD-OCT) and short-wavelength fundus autofluorescence (SW-FAF).

RESULTS

We detected no vector-related or systemic toxicities. VA returned to within 15 letters of baseline in all but two patients (one developed acute foveal thinning, another patient, a macular hole); the rest showed no gross changes in foveal structure at two years. There were no significant differences between intervention and control eyes in mean light-adapted sensitivity by perimetry, or in the lateral extent of retinal pigment epithelium (RPE) relative preservation by SD-OCT and SW-FAF. Microperimetry showed non-significant (<3SD of the intervisit variability) gains in sensitivity in some locations and participants in the intervention eye. There were no obvious dose-dependent relationships.

CONCLUSIONS

VA was within 15 letters of baseline after the subfoveal AAV2-hCHM injections in 13/15 (87%) of the patients. Acute foveal thinning with unchanged perifoveal function in one patient and macular hole in a second suggests foveal vulnerability to the subretinal injections. Longer observation intervals will help establish the significance of the minor differences in sensitivities and rate of disease progression observed between intervention and control eyes.

Multimodal imaging reveals retinoschisis masquerading as retinal detachment in patients with choroideremia

Purpose

To report three cases of retinoschisis in patients with intermediate to advanced choroideremia.

Observations

Three patients were referred for evaluation of retinal detachment in the context of an inherited retinal degenerative disease. In all three cases, patients carried variants in the CHM gene suspected to be pathogenic and exhibited the characteristic findings of choroideremia, including pigment clumping and chorioretinal atrophy with scleral exposure and prominent choroidal vessels. Interestingly, these patients were also found to have areas of typical retinoschisis and cystoid degeneration located in the outer plexiform layer of the mid periphery or macula. Retinoschisis was confirmed by spectral domain optical coherence tomography (SD-OCT).

Conclusions/Importance

This paper draws attention to the occurrence of retinoschisis in patients with choroideremia. OCT can be used to confirm the presence of retinoschisis rather than retinal detachment, as the clinical exam findings that distinguish the two conditions are not helpful in the setting of advanced chorioretinal atrophy. Although it remains unclear whether patients with choroideremia as a group are at increased risk of retinoschisis, it is possible that abnormal vesicular traffic in the RPE and photoreceptors could contribute to abnormalities in cell adhesion and the extracellular matrix. As gene therapy by subretinal injection of adeno-associated virus becomes the standard of care to slow down or arrest retinal degeneration in choroideremia, it will be critical to carefully screen these patients for retinoschisis prior to surgical intervention and to incorporate any such findings into surgical planning.

Adeno-Associated Viral Vectors as Versatile Tools for Neurological Disorders: Focus on Delivery Routes and Therapeutic Perspectives

It is without doubt that the gene therapy field is currently in the spotlight for the development of new therapeutics targeting unmet medical needs. Thus, considering the gene therapy scenario, neurological diseases in general and neurodegenerative disorders in particular are emerging as the most appealing choices for new therapeutic arrivals intended to slow down, stop, or even revert the natural progressive course that characterizes most of these devastating neurodegenerative processes. Since an extensive coverage of all available literature is not feasible in practical terms, here emphasis was made in providing some advice to beginners in the field with a narrow focus on elucidating the best delivery route available for fulfilling any given AAV-based therapeutic approach. Furthermore, it is worth nothing that the number of ongoing clinical trials is increasing at a breath-taking speed. Accordingly, a landscape view of preclinical and clinical initiatives is also provided here in an attempt to best illustrate what is ongoing in this quickly expanding field.

Clinical Manifestations and Genetic Analysis of 5 Korean Choroideremia Patients Initially Diagnosed With Retinitis Pigmentosa

BACKGROUND

To investigate the clinical findings of choroideremia patients and perform genetic analysis by whole-exome sequencing (WES).

METHODS

A total of 94 patients initially diagnosed with retinitis pigmentosa (RP) at another hospital, and who visited our hospital for genetic analysis by WES, were included in the study, along with 64 family members. All subjects underwent comprehensive ophthalmic evaluation, including best-corrected visual acuity, slit lamp examination, fundus photography, fundus autofluorescence (FAF), fluorescein angiography (FAG), visual field (VF), electroretinogram (ERG), and optical coherence tomography (OCT).

RESULTS

In six male patients with suspected choroideremia, extensive retinal pigment epithelium (RPE) and severe loss of choroid were observed in the fundus, but not in the macula. CHM gene mutation was confirmed in five patients. A novel single nucleotide variant at a splice site was observed in one patient. OCT showed marked thinning of the outernuclear layer and choroid, except in the macula. FAF showed a small area of hyperfluorescence in the posterior pole. In addition, characteristic interlaminar bridges were observed in four patients. On FAG, hypofluorescence was seen up to the far-peripheral retina in five patients.

CONCLUSION

Of the 94 patients initially diagnosed with RP, CHM mutation was identified in five (5.3%) by WES. Choroideremia should be considered as a differential diagnosis of RP. WES would be useful for identifying the causes of hereditary retinal disease.

[Morphology of outer retinal tubulations in the outcome of exudative age-related macular degeneration according to optical coherence tomography angiography]

Outer retinal tubulation (ORT) develops in the later stages of age-related macular degeneration (AMD). It is associated with low visual acuity, severe loss of photoreceptors, choroidal neovascularization (CNV), and geographic atrophy. Despite the frequent detection of ORTs by optical coherence tomography (OCT), their role in the process of outer retinal atrophy and degenerative changes in photoreceptors remains undetermined.

PURPOSE

To investigate the evolution of ORT in patients with exudative and disciform-stage CNV.

MATERIAL AND METHODS

The retrospective study included 340 patients with AMD, among them 235 (69%) women and 105 (31%) men with mean age of 76±7.4 years; in all, the analysis involved 267 eyes with dry AMD and 174 eyes with CNV: 92 eyes - with exudative AMD, 82 eyes - with disciform-stage disease). In addition to standard OCT, all patients underwent OCT-angiography (OCTA). In 10 cases, patients with exudative AMD were followed up after intravitreal injections of Aflibercept.

RESULTS

ORTs were detected in 37 eyes of 32 patients (26%), all of them with CNV: 13 eyes with exudative AMD (group 1) and 24 eyes with disciform scar (group 2; p=0.013).

The groups were similar in the type and morphology of ORTs. The most common were closed, i.e. fully formed ORT (92% of cases in group 1, and 88% in group 2). Destruction of the ellipsoid zone associated with ORT was observed in both groups. In one case, there was an increase in the size of ORT corresponding to the volume of cystic macular edema. Disappearance of ORT was noted only in one of ten patients 3 months after intravitreal injection of Aflibercept, but was not accompanied by visual acuity improvement.

CONCLUSION

Outer retinal tubulations are more common in the later stages of AMD, being an indicator of a deep destructive process in photoreceptors. In exudative AMD, ORTs serve as a predictive marker for poor functional outcomes.

HYPERREFLECTIVE FOCI AS A PATHOGENETIC BIOMARKER IN CHOROIDEREMIA

PURPOSE

To assess hyperreflective foci (HF) number and distribution in choroideremia (CHM) using spectral domain optical coherence tomography.

METHODS

Observational, cross-sectional case series. Consecutive patients and matched controls (20 eyes each) underwent best-corrected visual acuity measurement, fundoscopy, blue-light autofluorescence (BL-FAF) and spectral domain optical coherence tomography. Hyperreflective foci were assessed on a horizontal spectral domain optical coherence tomography scan, in the 500-µm area centered on the umbo, and in the 500-μm-wide areas internal (preserved border) and external (pathologic border) to the chorioretinal atrophy of CHM patients, and in the parafovea of controls. Hyperreflective foci were subclassified as retinal or choroidal. The spared central islet was measured on BL-FAF. Primary outcome was HF quantification in CHM. Secondary outcomes included their relationships with atrophy extent.

RESULTS

Choroideremia eyes disclosed a significantly higher HF number across the pathologic border and in the fovea when compared with controls; in particular, these HF were primarily located in the choroid (59-87%). Moreover, choroidal HF in the pathologic border inversely correlated with the area of the preserved central islet.

CONCLUSION

Hyperreflective foci might turn out to be a potential biomarker of CHM activity or severity. In this regard, we hypothesize that HF may be related to macrophages activation or progressive retinal pigment epithelium degeneration.

CHOROIDAL VASCULARITY INDEX IN YOUNG CHOROIDEREMIA PATIENTS

PURPOSE

To evaluate choroidal features in young patients affected by choroideremia (CHM).

METHODS

Young CHM patients and control subjects were recruited at the Eye Clinic in Florence. High-resolution choroidal imaging was obtained using swept-source optical coherence tomography with long optical coherence tomography scans (12 × 9 mm optical coherence tomography scans). We considered the subfoveal choroidal area within 9 mm of the optic disk in the horizontal plane and the subfoveal choroidal area within a 3-mm diameter centered over the fovea. The subfoveal choroidal thickness, total choroidal area, luminal area, stromal area, and choroidal vascularity index were assessed using the "ImageJ" software in both groups.

RESULTS

Eight patients (16 eyes; mean age, 19.3 ± 5.2 years) and seven control subjects (14 eyes; mean age, 19.0 ± 5.0 years) were included in this study. Best-corrected visual acuity was 20/20 in both eyes of seven CHM patients and in all control subjects and 20/25 in both eyes in one CHM patient. Mean subfoveal choroidal thickness did not differ between CHM patients and control subjects. Luminal area9mm, stromal area9mm, and total choroidal area9mm were reduced in patients compared with the control group. Luminal area3mm, stromal area3mm, and total choroidal area3mm did not differ between patients and control subjects. Choroidal vascularity index9mm and choroidal vascularity index3mm were not different between patients and control subjects.

CONCLUSION

There are no differences in the choroidal vascularity index between young CHM patients and control subjects; this result suggests a simultaneous, proportional impairment of both the stromal and vascular components of the choroid in the early stages of the disease.

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.

Choroidal Vascularity Features in Patients with Choroideremia and Cystoid Spaces

Cystoid spaces (CSs) are a common retinal finding in choroideremia (CHM) patients. The aim of this study was to analyze the vascular features of the choroid associated with the presence of CSs in patients with confirmed genetic diagnosis of CHM. A total of 33 patients (33 eyes) were enrolled in this retrospective cross-sectional study and divided into two groups based on the presence (17 eyes) or absence (16 eyes) of CSs. Choroidal features were evaluated on spectral-domain optical coherence tomography including subfoveal choroidal thickness (CT), total choroidal area (TCA), luminal choroidal area (LCA), and stromal choroidal area (SCA). The choroidal vascularity index (CVI) was then calculated in all study eyes. All structural choroidal parameters were calculated both on the entire length of the B-scan and in the central subfoveal 1500 μm. The average age was 37.3 ± 11.6 and 31.4 ± 16.7 years (p = 0.25) and mean logMAR best-corrected visual acuity was 0.11 ± 0.20 and 0.20 ± 0.57 (p = 0.54) in the CHM groups with and without CSs, respectively. There were no significant differences in subfoveal CT, and TCA, LCA, SCA, and CVI evaluated on either the entire scan or in the central 1500 μm (all p > 0.05). All choroidal vasculature parameters exhibited no significant differences between CHM eyes with and without CSs. Our results suggest that the choroid may not be involved in the development of CSs in patients with CHM.

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.

Study of retinal structural-functional relationship in choroideremia using fundus autofluorescence and optical coherence tomography

OBJECTIVE

The objective of this study was to assess the structural-functional relationship in choroideremia (CHM) patients using optical coherence tomography (OCT) and autofluorescence (AF) images.

METHODS

In this study, 53 eyes of 28 CHM patients were included. Demographic, ocular and clinical fundus features were recorded. Fundus AF and OCT images were analysed. Patients were classified into two groups based on AF features: group 1, CHM patients where the foveal island was present and group 2, CHM patients where the foveal island was absent. Inner and outer retinal layer thicknesses, retinal pigment epithelium (RPE) and subfoveal choroidal thickness (SFCT) were measured and correlated with visual acuity (VA).

RESULTS

There were 26 eyes in group 1 and 27 eyes in group 2. Mean age in groups 1 and 2 were 51.7 ± 13.4 and 63.6 ± 11.6 years, respectively. Age (p = 0.001) and VA (p < 0.001) between the two groups were significantly different. The retinal and SFCT showed significant differences that were analysed for each eye between the two groups. Reduced VA was noted with increasing age (r = 0.483; p ≤ 0.001), thin total retina (r = -0.378; p = 0.005), inner (r = -0.512; p < 0.001), outer (r = -0.59; p < 0.001) retinal thicknesses and thin RPE (r = -0.653; p < 0.001). Multivariate analysis showed RPE thickness (p = 0.001) as the most important index that affected VA.

CONCLUSION

RPE thinning contributes to poor VA in patients with advanced CHM. Further studies are needed to evaluate the role of retinal thickness and SFCT and its relationship to VA.

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.

Longitudinal Study to Assess the Quantitative Use of Fundus Autofluorescence for Monitoring Disease Progression in Choroideremia

Background: Characterisation of preserved autofluorescence (PAF) area in choroideremia (CHM) and its validity for monitoring disease progression in clinical trials is of importance. Methods: Eighty patients with molecularly confirmed CHM were recruited. PAF area was measured manually by 2 graders and half-life was calculated based on exponential decay model. Results: Mean age at baseline and follow-up examination was 38.1 (range, 10–69) and 40.7 (range, 11–70) years. Mean follow-up interval was 29 months (range, 6–104). The median LogMAR visual acuity was 0.10 (OD) and 0.18 (OS). Interobserver repeatability for PAF area was −0.99 to 1.03 mm² (−6.46 to 6.49% of area). There was a statistically significant relationship between age and rate of PAF area loss (r² = 0.28, p = 0.012). The half-life for PAF area was 13.7 years (range, 1.7–216.0 years). The correlation between half-life and age was stronger than between half-life and log transformed baseline PAF area, although neither was statistically significant. Conclusions: The intra- and inter-observer PAF area measurement variability provides a baseline change, which must be overcome in a clinical trial if this metric were to be used. Treatments must slow progression to alter the exponential decay in a timely manner accounting for naturally slow progression patterns.

The role of multimodal imaging and vision function testing in ABCA4-related retinopathies and their relevance to future therapeutic interventions

The aim of this review article is to describe the specific features of Stargardt disease and ABCA4 retinopathies (ABCA4R) using multimodal imaging and functional testing and to highlight their relevance to potential therapeutic interventions. Standardised measures of tissue loss, tissue function and rate of change over time using formal structured deep phenotyping in Stargardt disease and ABCA4R are key in diagnosis, and prognosis as well as when selecting cohorts for therapeutic intervention. In addition, a meticulous documentation of natural history will be invaluable in the future to compare treated with untreated retinas. Despite the familiarity with the term Stargardt disease, this eponymous classification alone is unhelpful when evaluating ABCA4R, as the ABCA4 gene is associated with a number of phenotypes, and a range of severity. Multimodal imaging, psychophysical and electrophysiologic measurements are necessary in diagnosing and characterising these differing retinopathies. A wide range of retinal dystrophy phenotypes are seen in association with ABCA4 mutations. In this article, these will be referred to as ABCA4R. These different phenotypes and the existence of phenocopies present a significant challenge to the clinician. Careful phenotypic characterisation coupled with the genotype enables the clinician to provide an accurate diagnosis, associated inheritance pattern and information regarding prognosis and management. This is particularly relevant now for recruiting to therapeutic trials, and in the future when therapies become available. The importance of accurate genotype-phenotype correlation studies cannot be overemphasised. This approach together with segregation studies can be vital in the identification of causal mutations when variants in more than one gene are being considered as possible. In this article, we give an overview of the current imaging, psychophysical and electrophysiological investigations, as well as current therapeutic research trials for retinopathies associated with the ABCA4 gene.

Differences in Intraretinal Pigment Migration Across Inherited Retinal Dystrophies

PURPOSE

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

DESIGN

Retrospective cohort study.

METHODS

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

RESULTS

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

CONCLUSIONS

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

Fluorescence Lifetime Imaging Ophthalmoscopy (FLIO) in Patients with Choroideremia

Purpose

To provide a detailed characterization of choroideremia (CHM) using fluorescence lifetime imaging ophthalmoscopy (FLIO) and to provide a deeper understanding of disease-related changes and progression.

Methods

Twenty-eight eyes of 14 patients with genetically confirmed CHM (mean age, 28 ± 14 years) and 14 age-matched healthy subjects were investigated in this study. FLIO images of a 30° retinal field were collected at the Moran Eye Center using a Heidelberg Engineering FLIO device. FLIO lifetimes were recorded in short spectral channels (SSC; 498-560 nm) and long spectral channels (LSC; 560-720 nm), and mean autofluorescence lifetimes (τm) were calculated. Optical coherence tomography (OCT) scans were recorded for each patient. Three patients were re-imaged after a year.

Results

Patients with CHM exhibit specific FLIO lifetime patterns. Prolonged FLIO lifetimes (around 600-700 ps) were found in the peripheral macula corresponding to atrophy in OCT imaging. In the central macula, τm was unrelated to autofluorescence intensity. Some areas of persistent retinal pigment epithelial islands had prolonged FLIO lifetimes, whereas other areas of hypofluorescence had short FLIO lifetimes. At 1-year follow-up, FLIO lifetimes were significantly prolonged within atrophic areas (P < 0.05).

Conclusions

FLIO shows distinct patterns in patients with CHM, indicating lesions of atrophy and areas of preserved function in the presence or absence of findings in fundus autofluorescence intensity images. FLIO may provide differentiated knowledge about pathophysiology and atrophy progression in CHM compared to conventional imaging modalities.

Translational Relevance

FLIO shows distinctive lifetime patterns that potentially identify areas of function, atrophy, and disease progression in patients with CHM.

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.

VASCULAR ALTERATIONS REVEALED WITH OPTICAL COHERENCE TOMOGRAPHY ANGIOGRAPHY IN PATIENTS WITH CHOROIDEREMIA

PURPOSE

Choroideremia is a rare degenerative retinal disease that causes incurable blindness. It occurs as a result of the deficiency of the X-linked CHM gene, which encodes the Rab escort protein 1 (REP1). Gene therapy has been developed to treat CHM using adeno-associated viral vectors and is currently undergoing clinical trials. Expression of the CHM gene is ubiquitous throughout the retina, and it is therefore important to identify which retinal layers are affected in the disease process. The purpose of this study was to assess in particular the choriocapillaris using optical coherence tomography angiography because this layer is difficult to see with conventional imaging techniques.

METHODS

Six men with choroideremia were identified and underwent standardized optical coherence tomography angiography as part of an ethics-approved clinical study and were compared with age-matched control subjects.

RESULTS

The choriocapillaris appeared normal in regions where the retinal pigment epithelium remained intact, but it was deficient elsewhere. The outer retinal vasculature showed significant changes peripherally but also some changes centrally. The inner retinal vasculature appeared unaffected by the disease process.

CONCLUSION

Choroideremia is a disease in which the choriocapillaris maintains a normal structure until the loss of the overlying retinal pigment epithelium. The inner retina also appears not to be affected at the vascular level. Although this study is limited by the small number of patients eligible for inclusion in the study, the observations support the concept of targeting gene therapy to the retinal pigment epithelium and outer retina because there is no evidence of independent degeneration of the choriocapillaris.

Reduced vessel density in deep capillary plexus correlates with retinal layer thickness in choroideremia

Background

To assess retinal layer thickness in choroideremia (CHM) and to reveal its correlation with optical coherence tomography (OCT) angiography (OCTA) findings.

Methods

The study was designed as an observational, cross-sectional clinical series of patients with CHM, which included 14 CHM eyes and 14 age-matched controls. Multimodal imaging included OCT and OCTA. The vessel density (VD) of superficial capillary (SCP), deep capillary (DCP) and choriocapillaris (CC) plexuses was analysed by OCTA. The apparently preserved retinal islet and atrophic regions were investigated separately. Main outcome measures were as follows: best-corrected visual acuity (BCVA), total retinal layers, ganglion cell layer (GCL), inner plexiform layer (IPL), inner nuclear layer (INL), outer plexiform layer (OPL), outer nuclear layer (ONL), ellipsoid zone–retinal pigment epithelium (EZ-RPE) layer, choroidal thickness and VDs of SCP, DCP and of CC.

Results

Mean BCVA was 0.0±0.0 LogMAR in both groups. GCL, ONL, EZ-RPE and choroid were significantly thinned in CHM, particularly in the atrophic region. OPL was unaffected in the apparently preserved islet, whereas INL and IPL were similarly thinned in the atrophic and apparently preserved retina. DCP appeared severely affected in both regions, while CC was only altered in the atrophic retina. Significant correlations were found between OCT and OCTA parameters.

Conclusions

Our study showed severe alterations in both outer and inner retinal layers of patients with CHM. The extended retinal involvement might be the consequence of neuronal and vascular trophic factor reduction produced by the primarily altered RPE and/or secondary Müller glial cell reaction.

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.

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.

A distinct retinal pigment epithelial cell autofluorescence pattern in choroideremia predicts early involvement of overlying photoreceptors

PURPOSE

Choroideremia is an X-linked retinal disease characterized by early retinal pigment epithelium (RPE) loss and subsequent retinal degeneration. The RPE adopts either a smooth or mottled appearance on fundus autofluorescence (FAF). It is not known how RPE changes predict the health of the overlying ellipsoid zone (EZ).

METHODS

A retrospective review of FAF and optical coherence tomography (OCT) images from 20 patients with choroideremia was performed. The percentage of intact EZ in each smooth and mottled FAF region was determined using one horizontal trans-foveal OCT section.

RESULTS

Fourteen out of 20 patients had distinct smooth and mottled areas in both eyes and were included in the sub-analysis. On average, 62.5 ± 10.1% of the EZ in each smooth region of the right eyes was intact compared to 10.0 ± 4.3% in the mottled areas. The same trend was observed in left eyes: 76.5 ± 7.2% of the EZ was intact in the smooth regions versus 9.8 ± 3.9% in the mottled areas (two-way anova, p < 0.0001). Thus, the mottled FAF regions were associated with EZ disruption more so than the smooth areas.

CONCLUSION

Retinal pigment epithelium (RPE) changes correlate with the health of the overlying EZ in choroideremia. The smooth FAF region likely represents early stages of the disease, with most of the area containing preserved EZ, whereas the mottled zone indicates more advanced stages and has mostly disrupted EZ. Because of the clear relationship between FAF findings and EZ integrity, FAF imaging can be used to monitor disease progression and identify areas of preserved EZ that could be rescued by gene therapy.

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.

En face OCT in choroideremia

Purpose: To describe the outer retinal tubulation (ORT) morphology using En face OCT elaboration in a large group of patients affected by choroideremia (CHM).Material and Methods: We retrospectively reviewed CHM patients examined at the Regional Reference Center for Hereditary Retinal Degenerations at the Eye Clinic in Florence. We took into consideration genetically confirmed CHM patients with ophthalmological, fundus autofluorescence (FAF) and optical coherence tomography (OCT) examinations.Results: We studied en face OCT features of ORTs in 18 CHM patients, for a total of 36 eyes; (average age 33 years; SD 19,2; range 13-77 years). ORTs were found in 30 eyes of 15 patients (15/18; 83,3% of the patients). We identified 3 en face OCT patterns: round lesions with scalloped boundaries which involved the peripapillary area with more or less evident pseudodendritic ORTs (PD-ORT) (pattern p; 26,7%); central islands with PD-ORTs (pattern i; 53,3%); residual outer retinal areas with no ORTs (pattern r; 20,0%).Conclusions: In CHM, en face OCT imaging allows us to observe various morphological features of the ORTs in different stages of disease, not detectable with other imaging techniques. ORTs were not identified in the mildest phenotypes. En face OCT is a non-invasive useful tool in the characterization and monitoring of the disease.

CLINICAL CHARACTERISTICS AND MOLECULAR GENETIC ANALYSIS OF A COHORT OF CHINESE PATIENTS WITH CHOROIDEREMIA

PURPOSE

To describe the clinical and molecular genetic characteristics of a large cohort of Chinese patients with choroideremia (CHM).

METHODS

Forty-eight Chinese participants from 35 families with a clinical diagnosis of CHM who harbored sequence variants in the CHM gene were enrolled. Comprehensive clinical evaluations and molecular genetic analysis of the CHM gene were performed.

RESULTS

The median age of the 48 patients was 31.5 years (range, 5-78 years). There were 30 different sequence variants detected in 35 families; of which, 13 sequence variants were novel. The mean (±SD) best-corrected visual acuity best in logarithm of the minimum angle of resolution equivalents was 0.71 (±0.87) (range, 0.00-2.80) or approximately 20/100 in Snellen visual acuity. A significant correlation was revealed between best-corrected visual acuity best and age (P < 0.001). The trend in the change in the best-corrected visual acuity over age showed that relatively good vision remained until 20 years old. The patterns of fundus photography and fundus autofluorescence finding demonstrated that residual retinal pigment epithelium areas significantly declined in patients at the age of 20 years or older. The results of visual field and full-field electroretinography showed that these measures might be of limited value for evaluating the condition of the late stage of CHM in Chinese patients.

CONCLUSION

This study described for the first time the clinical and molecular genetic characteristics of a large cohort of Chinese patients with CHM. The findings from best-corrected visual acuity best and visual field showed that the impairment of visual function in CHM might be more severe in Chinese patients than in western patients.

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

Purpose

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

Methods

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

Results

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

Conclusions

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

Choroideremia: Update On Clinical Features And Emerging Treatments

Choroideremia (CHM) is an X-linked chorioretinal dystrophy characterized by progressive degeneration of the choroid, retinal pigment epithelium and retina. This disease is caused by mutations in the X-linked CHM gene encoding a Ras-related GTPase Rab escort protein (REP)-1, which is extremely important for the retinal function. Clinically, male-affected patients have a progressive reduction in visual acuity. This disease is formally considered incurable, although new promising treatments have been recently introduced. In this article, a review of the salient pathogenetic features of choroideremia, essential for the proper interpretation of therapeutic approaches, is followed by a discussion of the fundamental clinical features of this hereditary disease. Finally, relevant new therapeutic approaches in this disease will be discussed, including gene therapy, stem cells, small molecules, and retinal prosthesis.

The Impact of Progressive Visual Field Constriction on Reading Ability in an Inherited Retinal Degeneration

BACKGROUND

The ability to read is an important factor in the quality of life. Choroideremia is an inherited retinal degeneration presenting with gradual, progressive constriction of the central visual field, providing a useful disease model to investigate the impact of the visual field on reading ability.

OBJECTIVE

The aim of this study was to provide practical guidance on the usefulness of measuring reading ability in patients.

METHOD

The Radner Reading Test was administered to 33 patients (65 eyes with choroideremia). To quantify the residual retinal area, the patients underwent microperimetry and imaging. The visual angle subtended by the largest letter read by each subject was calculated using Emsley's Model Eye.

RESULTS

A minimum of 1 letter must be seen to allow the eye to read, with preservation of foveal sensitivity. The relationship between reading speed and acuity varies with the visual field. The reading speed is higher in eyes with an intact fovea (p < 0.001 right eye, p = 0.06 left eye). Qualitative analysis of the direction of the intact retina did not indicate any directional impact on measurements.

CONCLUSIONS

In order to read, an eye must have enough retinal width close to the fovea to see at least 1 full letter. Direction of print does not impact the ability to read, allowing results from different languages to be combined in clinical trials.

Optical coherence tomography (OCT) features of cystoid spaces in choroideremia (CHM)

PURPOSE

To investigate the prevalence and features of cystoid spaces (CS) in patients with confirmed genetic diagnosis of choroideremia (CHM) using swept source optical coherence tomography (OCT).

METHODS

We retrospectively reviewed CHM patients examined at the Regional Reference Center for Hereditary Retinal Degenerations at the Eye Clinic in Florence. We took into consideration genetically confirmed CHM patients with ophthalmological and swept source optical coherence tomography (OCT) examinations. The presence/absence and location of cystoid spaces in the retina of each eye were reported.

RESULTS

A total of 42 eyes of 21 CHM patients were included in our series. The average age of the patients was 36.5 ± 20.1 (range, 13-73 years). The average best-corrected visual acuity (BCVA) for all patients was 0.63 ± 1.00 logMar (range, 0-2,80). CS were present in 15 eyes of eight patients (8/21, 38%). In all cases, CS were located in inner nuclear layer (INL); in five eyes of three patients, CS were detected also in ganglion cell layer (GCL). CS appeared as microcistoyd abnormalities and were detected in retinal areas characterized by retinal pigment epithelium (RPE) and outer retinal layers atrophy at the transition zone.

CONCLUSIONS

Cystoid spaces in choroideremia showed peculiar features; they are clusters of small-size extrafoveal degenerative cysts mainly located in inner nuclear layer at the transition zone where outer retinal layers and RPE are severely damaged.

Molecular Therapies for Choroideremia

Advances in molecular research have culminated in the development of novel gene-based therapies for inherited retinal diseases. We have recently witnessed several groundbreaking clinical studies that ultimately led to approval of Luxturna, the first gene therapy for an inherited retinal disease. In parallel, international research community has been engaged in conducting gene therapy trials for another more common inherited retinal disease known as choroideremia and with phase III clinical trials now underway, approval of this therapy is poised to follow suit. This chapter discusses new insights into clinical phenotyping and molecular genetic testing in choroideremia with review of molecular mechanisms implicated in its pathogenesis. We provide an update on current gene therapy trials and discuss potential inclusion of female carries in future clinical studies. Alternative molecular therapies are discussed including suitability of CRISPR gene editing, small molecule nonsense suppression therapy and vision restoration strategies in late stage choroideremia.

Near-Infrared Autofluorescence in Choroideremia: Anatomic and Functional Correlations

PURPOSE

To investigate near-infrared fundus autofluorescence (NIR-AF) characteristics in patients with choroideremia and to correlate these with anatomic and functional parameters.

DESIGN

Retrospective, observational case series.

METHODS

In this multicenter study, 43 consecutive choroideremia patients (79 eyes) underwent multimodal retinal imaging, including near-infrared fundus autofluorescence (NIR-AF), blue autofluorescence (B-AF), optical coherence tomography (OCT), fundus photography, and functional testing including fundus-controlled microperimetry.

RESULTS

All eyes could be categorized into 3 groups based on patterns of NIR-AF over the island of surviving retinal pigment epithelium: Group 1 (preserved NIR-AF centrally), Group 2 (only disrupted NIR-AF), or Group 3 (absence of NIR-AF). Group 1 eyes showed areas of NIR-AF that matched the areas of B-AF islands (R² = 0.94, slope 0.84 ± 0.04) while Group 2 eyes showed significantly smaller areas of NIR-AF compared with B-AF (R² = 0.08; slope 0.02 ± 0.01). The 3 groups differed significantly in terms of residual B-AF island size (P < .0001), length of foveal ellipsoid zone (P = .03), foveal thickness (P = .04), and foveal sensitivity (P = .01). Visual acuity (P = .07) and central retinal thickness (P = .06) did not differ statistically. The length of the ellipsoid zone line was similar to the horizontal diameter of NIR-AF in Group 1 (R² = 0.97, slope 0.96 ± 0.04), while Group 2 eyes showed broader ellipsoid zone than NIR-AF (R² = 0.60, slope 0.19 ± 0.03).

CONCLUSIONS

Choroideremia patients can be stratified into 3 groups based on NIR-AF imaging, which showed morphologic and functional changes correlating with different stages of retinal pigment epithelium degeneration. NIR-AF could be a marker for disease staging in choroideremia, and could be used for patient selection or as an outcome parameter in interventional trials.

Adeno-Associated Viral Gene Therapy for Inherited Retinal Disease

Inherited retinal diseases (IRDs) are a group of rare, heterogenous eye disorders caused by gene mutations that result in degeneration of the retina. There are currently limited treatment options for IRDs; however, retinal gene therapy holds great promise for the treatment of different forms of inherited blindness. One such IRD for which gene therapy has shown positive initial results is choroideremia, a rare, X-linked degenerative disorder of the retina and choroid. Mutation of the CHM gene leads to an absence of functional Rab escort protein 1 (REP1), which causes retinal pigment epithelium cell death and photoreceptor degeneration. The condition presents in childhood as night blindness, followed by progressive constriction of visual fields, generally leading to vision loss in early adulthood and total blindness thereafter. A recently developed adeno-associated virus-2 (AAV2) vector construct encoding REP1 (AAV2-REP1) has been shown to deliver a functional version of the CHM gene into the retinal pigment epithelium and photoreceptor cells. Phase 1 and 2 studies of AAV2-REP1 in patients with choroideremia have produced encouraging results, suggesting that it is possible not only to slow or stop the decline in vision following treatment with AAV2-REP1, but also to improve visual acuity in some patients.

Choroideremia: from genetic and clinical phenotyping to gene therapy and future treatments

Choroideremia is an X-linked inherited chorioretinal dystrophy leading to blindness by late adulthood. Choroideremia is caused by mutations in the CHM gene which encodes Rab escort protein 1 (REP1), an ubiquitously expressed protein involved in intracellular trafficking and prenylation activity. The exact site of pathogenesis remains unclear but results in degeneration of the photoreceptors, retinal pigment epithelium and choroid. Animal and stem cell models have been used to study the molecular defects in choroideremia and test effectiveness of treatment interventions. Natural history studies of choroideremia have provided additional insight into the clinical phenotype of the condition and prepared the way for clinical trials aiming to investigate the safety and efficacy of suitable therapies. In this review, we provide a summary of the current knowledge on the genetics, pathophysiology, clinical features and therapeutic strategies that might become available for choroideremia in the future, including gene therapy, stem cell treatment and small-molecule drugs with nonsense suppression action.

Beneficial effects on vision in patients undergoing retinal gene therapy for choroideremia

Retinal gene therapy is increasingly recognized as a novel molecular intervention that has huge potential in treating common causes of blindness, the majority of which have a genetic aetiology1-5. Choroideremia is a chronic X-linked retinal degeneration that was first described in 18726. It leads to progressive blindness due to deficiency of Rab-escort protein 1 (REP1). We designed an adeno-associated viral vector to express REP1 and assessed it in a gene therapy clinical trial by subretinal injection in 14 patients with choroideremia. The primary endpoint was vision change in treated eyes 2 years after surgery compared to unoperated fellow eyes. Despite complications in two patients, visual acuity improved in the 14 treated eyes over controls (median 4.5 letter gain, versus 1.5 letter loss, P = 0.04), with 6 treated eyes gaining more than one line of vision (>5 letters). The results suggest that retinal gene therapy can sustain and improve visual acuity in a cohort of predominantly late-stage choroideremia patients in whom rapid visual acuity loss would ordinarily be predicted.

THE NATURAL HISTORY OF FULL-FIELD STIMULUS THRESHOLD DECLINE IN CHOROIDEREMIA

PURPOSE

To evaluate full-field sensitivity thresholds (FSTs) across a wide range of choroideremia (CHM) disease stages and to determine their applicability as functional endpoints for CHM clinical trials.

METHODS

Thirty CHM subjects (60 eyes) and 50 healthy controls (50 eyes) underwent FST testing under dark-adapted conditions to determine rod- and cone-mediated FSTs. Central retinal structure and function were assessed using fundus autofluorescence and microperimetry. Correlation and regression analyses were performed to compare FST responses with the residual area of retinal pigment epithelium in the peri- and parafoveal regions, as well as the mean and highest macular microperimetry sensitivity.

RESULTS

All patients with CHM had a baseline of 18 dB elevation in dark-adapted rod FSTs, including the least affected individuals. Further FST sensitivity loss was exponentially associated with decrease in the area of residual peri- and parafoveal retinal pigment epithelium, with precipitous loss of sensitivity noted for fundus autofluorescence areas less than 5 mm. Cone FSTs were comparable with controls, except for advanced stages of CHM. Full-field sensitivity threshold responses showed high correlation with both mean and highest macular microperimetry thresholds (P < 0.001). In some cases of absent macular fundus autofluorescence, the peripheral retina could contribute to detectable rod FST responses but with severely diminished cone-driven responses.

CONCLUSION

Full-field sensitivity threshold testing demonstrated a baseline level of rod dysfunction in CHM present in all rod photoreceptors. Further decline in FST responses correlated strongly with the extent of central retina structural and functional loss. Full-field sensitivity threshold allowed quantification of residual rod function in peripheral islands of vision, which cannot be reliably achieved with other conventional tests. As such, the FST can serve as a complimentary tool to guide patient selection and expand the eligibility criteria for current and future CHM clinical trials.

Gene editing in the context of an increasingly complex genome

The reporting of the first draft of the human genome in 2000 brought with it much hope for the future in what was felt as a paradigm shift toward improved health outcomes. Indeed, we have now mapped the majority of variation across human populations with landmark projects such as 1000 Genomes; in cancer, we have catalogued mutations across the primary carcinomas; whilst, for other diseases, we have identified the genetic variants with strongest association. Despite this, we are still awaiting the genetic revolution in healthcare to materialise and translate itself into the health benefits for which we had hoped. A major problem we face relates to our underestimation of the complexity of the genome, and that of biological mechanisms, generally. Fixation on DNA sequence alone and a 'rigid' mode of thinking about the genome has meant that the folding and structure of the DNA molecule -and how these relate to regulation- have been underappreciated. Projects like ENCODE have additionally taught us that regulation at the level of RNA is just as important as that at the spatiotemporal level of chromatin.In this review, we chart the course of the major advances in the biomedical sciences in the era pre- and post the release of the first draft sequence of the human genome, taking a focus on technology and how its development has influenced these. We additionally focus on gene editing via CRISPR/Cas9 as a key technique, in particular its use in the context of complex biological mechanisms. Our aim is to shift the mode of thinking about the genome to that which encompasses a greater appreciation of the folding of the DNA molecule, DNA- RNA/protein interactions, and how these regulate expression and elaborate disease mechanisms.Through the composition of our work, we recognise that technological improvement is conducive to a greater understanding of biological processes and life within the cell. We believe we now have the technology at our disposal that permits a better understanding of disease mechanisms, achievable through integrative data analyses. Finally, only with greater understanding of disease mechanisms can techniques such as gene editing be faithfully conducted.

Deep learning for the segmentation of preserved photoreceptors on en face optical coherence tomography in two inherited retinal diseases

The objective quantification of photoreceptor loss in inherited retinal degenerations (IRD) is essential for measuring disease progression, and is now especially important with the growing number of clinical trials. Optical coherence tomography (OCT) is a non-invasive imaging technology widely used to recognize and quantify such anomalies. Here, we implement a versatile method based on a convolutional neural network to segment the regions of preserved photoreceptors in two different IRDs (choroideremia and retinitis pigmentosa) from OCT images. An excellent segmentation accuracy (~90%) was achieved for both IRDs. Due to the flexibility of this technique, it has potential to be extended to additional IRDs in the future.