Choroideremia: new findings from ocular pathology and review of recent literature

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.

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.

Cone Photoreceptor Morphology in Choroideremia Assessed Using Non-Confocal Split-Detection Adaptive Optics Scanning Light Ophthalmoscopy

Purpose

Choroideremia (CHM) is an X-linked inherited retinal degeneration causing loss of the photoreceptors, retinal pigment epithelium, and choriocapillaris, although patients typically retain a central island of relatively preserved, functioning retina until late-stage disease. Here, we investigate cone photoreceptor morphology within the retained retinal island by examining cone inner segment area, density, circularity, and intercone space.

Methods

Using a custom-built, multimodal adaptive optics scanning light ophthalmoscope, nonconfocal split-detection images of the photoreceptor mosaic were collected at 1°, 2°, and 4° temporal to the fovea from 13 CHM and 12 control subjects. Cone centers were manually identified, and cone borders were segmented. A custom MATLAB script was used to extract area and circularity for each cone and calculate the percentage of intercone space in each region of interest. Bound cone density was also calculated. An unbalanced two-way ANOVA and Bonferroni post hoc tests were used to assess statistical differences between the CHM and control groups and along retinal eccentricity.

Results

Cone density was lower in the CHM group than in the control group (P < 0.001) and decreased with eccentricity from the fovea (P < 0.001). CHM cone inner segments were larger in area (P < 0.001) and more circular (P = 0.042) than those of the controls. Intercone space in CHM was also higher than in the controls (P < 0.001).

Conclusions

Cone morphology is altered in CHM compared to control, even within the centrally retained, functioning retinal area. Further studies are required to determine whether such morphology is a precursor to cone degeneration.

Widespread subclinical cellular changes revealed across a neural-epithelial-vascular complex in choroideremia using adaptive optics

Choroideremia is an X-linked, blinding retinal degeneration with progressive loss of photoreceptors, retinal pigment epithelial (RPE) cells, and choriocapillaris. To study the extent to which these layers are disrupted in affected males and female carriers, we performed multimodal adaptive optics imaging to better visualize the in vivo pathogenesis of choroideremia in the living human eye. We demonstrate the presence of subclinical, widespread enlarged RPE cells present in all subjects imaged. In the fovea, the last area to be affected in choroideremia, we found greater disruption to the RPE than to either the photoreceptor or choriocapillaris layers. The unexpected finding of patches of photoreceptors that were fluorescently-labeled, but structurally and functionally normal, suggests that the RPE blood barrier function may be altered in choroideremia. Finally, we introduce a strategy for detecting enlarged cells using conventional ophthalmic imaging instrumentation. These findings establish that there is subclinical polymegathism of RPE cells in choroideremia.

Choroideremia Carriers: Dark-Adapted Perimetry and Retinal Structures

Purpose

In choroideremia (CHM) carriers, scotopic sensitivity was assessed by dark adapted chromatic perimetry (DACP) and outer retinal structure was evaluated by multimodal imaging.

Methods

Nine carriers (18 eyes) and 13 healthy controls (13 eyes) underwent DACP testing with cyan and red stimuli. Analysis addressed peripapillary (4 test locations closest to the optic disc), macular (52 locations), and peripheral (60 locations outside the macula) regions. Responses were considered to be rod-mediated when cyan relative to red sensitivity was >5 dB. Fundus imaging included spectral domain optical coherence tomography (SD-OCT), short-wavelength (SW-AF), near-infrared (NIR-AF), ultrawide-field (200 degrees) pseudocolor fundus imaging, and quantitative (qAF) fundus autofluorescence.

Results

Detection of the cyan stimulus was rod mediated in essentially all test locations (99.7%). In the macular and peripheral areas, DACP sensitivity values were not significantly different from healthy eyes. In the peripapillary area, sensitivities were significantly decreased (P < 0.05). SD-OCT imaging ranged from hyper-reflective lesions and discontinuities of the outer retinal bands to hypertransmission of signal. SW-AF and NIR-AF images presented with peripapillary atrophy in seven patients (14 eyes). Mosaicism was detectable in SW-AF images in seven patients and in NIR-AF images in five patients. Frank hypo-autofluorescence was visible in eight patients with distinct chorioretinopathy in seven patients. The qAF values were below the 95% confidence interval (CI) of healthy age-matched individuals in 12 eyes.

Conclusions

Rod mediated scotopic sensitivity was comparable to that in control eyes in macular and peripheral areas but was decreased in the peripapillary area where changes in retinal structure were also most severe.

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.

Single-cell-resolution map of human retinal pigment epithelium helps discover subpopulations with differential disease sensitivity

Regional phenotypic and functional differences in the retinal pigment epithelium (RPE) monolayer have been suggested to account for regional susceptibility in ocular diseases such as age-related macular degeneration (AMD), late-onset retinal degeneration (L-ORD), and choroideremia (CHM). However, a comprehensive description of human topographical RPE diversity is not yet available, thus limiting the understanding of regional RPE diversity and degenerative disease sensitivity in the eye. To develop a complete morphometric RPE map of the human eye, artificial intelligence–based software was trained to recognize, segment, and analyze RPE borders. Five statistically different, concentric RPE subpopulations (P1 to P5) were identified using cell area as a parameter, including a subpopulation (P4) with cell area comparable to that of macular cells in the far periphery of the eye. This work provides a complete reference map of human RPE subpopulations and their location in the eye. In addition, the analysis of cadaver non-AMD and AMD eyes and ultra-widefield fundus images of patients revealed differential vulnerability of the five RPE subpopulations to different retinal diseases.

Short-term Assessment of Subfoveal Injection of Adeno-Associated Virus-Mediated hCHM Gene Augmentation in Choroideremia Using Adaptive Optics Ophthalmoscopy

Importance

Subretinal injection for gene augmentation in retinal degenerations forcefully detaches the neural retina from the retinal pigment epithelium, potentially damaging photoreceptors and/or retinal pigment epithelium cells.

Objective

To use adaptive optics scanning light ophthalmoscopy (AOSLO) to assess the short-term integrity of the cone mosaic following subretinal injections of adeno-associated virus vector designed to deliver a functional version of the CHM gene (AAV2-hCHM) in patients with choroideremia.

Design, Setting, and Participants

This longitudinal case series study enrolled adult patients with choroideremia from February 2015 to January 2016 in the US. To be included in the study, study participants must have received uniocular subfoveal injections of low-dose (5 × 1010 vector genome per eye) or high-dose (1 × 1011 vector genome per eye) AAV2-hCHM. Analysis began February 2015.

Main Outcomes and Measures

The macular regions of both eyes were imaged before and 1 month after injection using a custom-built multimodal AOSLO. Postinjection cone inner segment mosaics were compared with preinjection mosaics at multiple regions of interest. Colocalized spectral-domain optical coherence tomography and dark-adapted cone sensitivity was also acquired at each time point.

Results

Nine study participants ranged in age from 26 to 50 years at the time of enrollment, and all were White men. Postinjection AOSLO images showed preservation of the cone mosaic in all 9 AAV2-hCHM-injected eyes. Mosaics appeared intact and contiguous 1 month postinjection, with the exception of foveal disruption in 1 patient. Optical coherence tomography showed foveal cone outer segment shortening postinjection. Cone-mediated sensitivities were unchanged in 8 of 9 injected and 9 of 9 uninjected eyes. One participant showed acute loss of foveal optical coherence tomography cone outer segment-related signals along with cone sensitivity loss that colocalized with disruption of the mosaic on AOSLO.

Conclusions and Relevance

Integrity of the cone mosaic is maintained following subretinal delivery of AAV2-hCHM, providing strong evidence in support of the safety of the injections. Minor foveal thinning observed following surgery corresponds with short-term cone outer segment shortening rather than cone cell loss. Foveal cone loss in 1 participant raises the possibility of individual vulnerability to the subretinal injection.

Lessons learned from research on choroideremia

Having devoted over 35 years of my professional life to various projects on choroideremia (CHM), I began to reflect on the many lessons that I learned along the way. One of the most important is: we should pay careful attention to possible, unintended psychological harm in clinical research. This lesson was learned early and then reinforced when I engaged CHM patients in an investigator-sponsored Phase IB clinical trial of ocular gene therapy for choroideremia. My second lesson came from the trial itself in that preliminary data may not be sufficient to predict the risks to patients in a clinical trial. In the significant push to begin a gene therapy trial for CHM patients, writing grants, recruiting personnel, interacting with regulatory authorities, acquiring research equipment to test outcome measures, I missed a third lesson. There is significant bias when the principal investigator of an investigator-sponsored clinical trial is also the treating physician in the trial. Ideally, those two roles should be kept separate. Finally, having completed the clinical trial, I learned that gene replacement with an AAV vector may not be the only genetic therapy for CHM; an antisense oligonucleotide therapy may be possible in select cases.

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.

Structural and Functional Characteristics of Color Vision Changes in Choroideremia

Color vision is considered a marker of cone function and its assessment in patients with retinal pathology is complementary to the assessments of spatial vision [best-corrected visual acuity (BCVA)] and contrast detection (perimetry). Rod-cone and chorioretinal dystrophies—such as choroideremia—typically cause alterations to color vision, making its assessment a potential outcome measure in clinical trials. However, clinical evaluation of color vision may be compromised by pathological changes to spatial vision and the visual field. The low vision Cambridge Color Test (lvCCT) was developed specifically to address these latter issues. We used the trivector version of the lvCCT to quantify color discrimination in a cohort of 53 patients with choroideremia. This test enables rapid and precise characterization of color discrimination along protan, deutan, and tritan axes more reliably than the historically preferred test for clinical trials, namely the Farnsworth Munsell 100 Hue test. The lvCCT demonstrates that color vision defects—particularly along the tritan axis—are seen early in choroideremia, and that this occurs independent of changes in visual acuity, pattern electroretinography and ellipsoid zone area on optical coherence tomography (OCT). We argue that the selective loss of tritan color discrimination can be explained by our current understanding of the machinery of color vision and the pathophysiology of choroideremia.

Choroidal Vascularity Index in CHM Carriers

Purpose

To assess the choroidal structure using the Choroidal Vascularity Index (CVI) and analyse choroidal changes in choroideremia (CHM) carriers.

Material and Methods

Female CHM carriers, genetically characterized, and a control group were recruited at the Eye Clinic of Careggi Teaching Hospital, Florence. The patients underwent a complete ophthalmic evaluation and retinal imaging. In particular, the Stromal Area (SA), Luminal Area (LA), Total Choroidal Area (TCA), CVI, and Subfoveal Choroidal Thickness (SFCT) were calculated for each eye using Optical Coherence Tomography (OCT) examinations.

Results

Twelve eyes of 6 CHM carriers and 14 eyes of 7 age-matched controls were analysed. The mean SFCT was 270.9 ± 54.3μm in carriers and 281.4 ± 36.8μm in controls (p = 0.564); LA was 0.99 ± 0.25mm2 and 1.01 ± 0.13mm2 (p = 0.172); SA was 0.53 ± 0.09mm2 and 0.59 ± 0.07mm2 (p = 0.075), and TCA was 1.53 ± 0.34mm2 and 1.69 ± 0.19mm2 respectively (p = 0.146). Mean CVI measured 64.03 ± 3.98% in the CHM carriers and 65.25 ± 2.55% in the controls (p = 0.360).

Conclusions

The CVI and CVI-related parameters (SA, LA, and TCA) do not differ between CHM female carriers and controls. These findings reveal a preserved choroidal vasculature in eyes with RPE impairment and support the primary role of RPE in the pathogenesis of CHM disease.

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.

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.

Comparing Fluorescence Lifetime Imaging Ophthalmoscopy in Atrophic Areas of Retinal Diseases

Purpose

Fluorescence lifetime imaging ophthalmoscopy (FLIO) is a non-invasive imaging modality to investigate the human retina. This study compares FLIO lifetimes in different degenerative retinal diseases.

Methods

Included were eyes with retinal pigment epithelium (RPE) and/or photoreceptor atrophy due to Stargardt disease (n = 66), pattern dystrophy (n = 18), macular telangiectasia type 2 (n = 49), retinitis pigmentosa (n = 28), choroideremia (n = 26), and geographic atrophy (n = 32) in age-related macular degeneration, as well as 37 eyes of 37 age-matched healthy controls. Subjects received Heidelberg Engineering FLIO, autofluorescence intensity, and optical coherence tomography imaging. Amplitude-weighted mean FLIO lifetimes (τ_m) were calculated and analyzed.

Results

Retinal FLIO lifetimes show significant differences depending on the disease. Atrophic areas in geographic atrophy and choroideremia showed longest mean FLIO lifetimes. τ_m values within areas of RPE and outer nuclear layer atrophy were significantly longer than within areas with preserved outer nuclear layer (P < 0.001) or non-atrophic areas (P < 0.001).

Conclusions

FLIO is able to contribute additional information regarding differences in chronic degenerative retinal diseases. Although it cannot replace conventional autofluorescence imaging, FLIO adds to the knowledge in these diseases and may help with the correct differentiation between them. This may lead to a more in-depth understanding of the pathomechanisms related to atrophy and types of progression.

Translational Relevance

Differences between atrophic retinal diseases highlighted by FLIO may indicate separate pathomechanisms leading to atrophy and disease progression.

Choroidal neovascularisation in a predicted female choroideraemia carrier treated with intravitreal anti-vascular endothelial growth factor

PURPOSE

To report a case of choroidal neovascularisation and leakage in a myopic female predicted to be a choroideraemia carrier treated with intravitreal anti-vascular endothelial growth factor (anti-VEGF).

METHODS

Case report.

RESULTS

A female magazine editor presented with sudden decrease in vision in her right eye, with Snellen visual acuities (VAs) of 1/60 and 3/60 in the right and left eyes respectively. She was diagnosed with choroidal neovascularisation (CNV) formation and subretinal haemorrhage in her right eye. This is on a background of previous presentations, the first of which was 20 years ago for declining left eye vision. She was subsequently found to be a predicted choroideraemia carrier. However, she also has high myopia, and it is unclear whether the predicted choroideraemia carrier status or high myopia is the main underlying cause of her CNV, although we believe that the former is more likely. The first episode of CNV in her right eye was treated successfully with intravitreal anti-VEGF. However, she experienced four further CNV reactivations in her right eye, all of which were treated successfully with anti-VEGF. At her last follow-up visit to date, Snellen VAs were 6/9 and 3/60 in her right and left eye respectively.

CONCLUSION

This is a unique case of CNV formation in a predicted choroideraemia carrier who also has co-existent high myopia. Prompt treatment of CNV activity with anti-VEGF has been efficacious in prevention of subretinal fibrosis and irreversible vision loss and allowed the patient to continue working in her chosen career.

Retinal Manifestations of Mitochondrial Oxidative Phosphorylation Disorders

Purpose

The purpose of this paper was to discuss manifestations of primary mitochondrial dysfunctions and whether the retinal pigment epithelium or the photoreceptors are preferentially affected.

Methods

A retrospective analysis was performed of patients with clinically and laboratory confirmed diagnoses of maternally inherited diabetes and deafness (MIDD) or Kearns–Sayre syndrome (KSS). Patients underwent full ophthalmic examination, full-field electroretinogram, and multimodal imaging studies, including short-wavelength autofluorescence, spectral domain-optical coherence tomography, and color fundus photography.

Results

A total of five patients with MIDD and four patients with KSS were evaluated at two tertiary referral centers. Mean age at initial evaluation was 50.3 years old. Nascent outer retinal tubulations corresponding with faint foci of autofluorescence were observed in two patients with MIDD. Characteristic features of this cohort included a foveal sparing phenotype observed in 13 of 18 eyes (72%), global absence of intraretinal pigment migration, and preserved retinal function on full-field electroretinogram testing in 12 of 16 eyes (75%). One patient diagnosed with MIDD presented with an unusual pattern of atrophy surrounding the parapapillary region and one patient with KSS presented with an atypical choroideremia-like phenotype.

Conclusions

MIDD and KSS are phenotypically heterogeneous disorders. Several features of disease suggest that primary mitochondrial dysfunction may first affect the retinal pigment epithelium followed by secondary photoreceptor loss. Similarities between primary mitochondrial degenerations and retinal disorders, such as age-related macular degeneration may suggest a primary role of mitochondria in the pathogenesis of these oligogenic disorders.

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.

Integrating adaptive optics-SLO and OCT for multimodal visualization of the human retinal pigment epithelial mosaic

In vivo imaging of human retinal pigment epithelial (RPE) cells has been demonstrated through multiple adaptive optics (AO)-based modalities. However, whether consistent and complete information regarding the cellular structure of the RPE mosaic is obtained across these modalities remains uncertain due to limited comparisons performed in the same eye. Here, an imaging platform combining multimodal AO-scanning light ophthalmoscopy (AO-SLO) with AO-optical coherence tomography (AO-OCT) is developed to make a side-by-side comparison of the same RPE cells imaged across four modalities: AO-darkfield, AO-enhanced indocyanine green (AO-ICG), AO-infrared autofluorescence (AO-IRAF), and AO-OCT. Co-registered images were acquired in five subjects, including one patient with choroideremia. Multimodal imaging provided multiple perspectives of the RPE mosaic that were used to explore variations in RPE cell contrast in a subject-, location-, and even cell-dependent manner. Estimated cell-to-cell spacing and density were found to be consistent both across modalities and with normative data. Multimodal images from a patient with choroideremia illustrate the benefit of using multiple modalities to infer the cellular structure of the RPE mosaic in an affected eye, in which disruptions to the RPE mosaic may locally alter the signal strength, visibility of individual RPE cells, or even source of contrast in unpredictable ways.

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.

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.

Chronically shortened rod outer segments accompany photoreceptor cell death in Choroideremia

X-linked choroideremia (CHM) is a disease characterized by gradual retinal degeneration caused by loss of the Rab Escort Protein, REP1. Despite partial compensation by REP2 the disease is characterized by prenylation defects in multiple members of the Rab protein family that are master regulators of membrane traffic. Remarkably, the eye is the only organ affected in CHM patients, possibly because of the huge membrane traffic burden of the post mitotic photoreceptors, which synthesise outer segments, and the adjacent retinal pigment epithelium that degrades the spent portions each day. In this study, we aimed to identify defects in membrane traffic that might lead to photoreceptor cell death in CHM. In a heterozygous null female mouse model of CHM (Chmnull/WT), degeneration of the photoreceptor layer was clearly evident from increased numbers of TUNEL positive cells compared to age matched controls, small numbers of cells exhibiting signs of mitochondrial stress and greatly increased microglial infiltration. However, most rod photoreceptors exhibited remarkably normal morphology with well-formed outer segments and no discernible accumulation of transport vesicles in the inner segment. The major evidence of membrane trafficking defects was a shortening of rod outer segments that was evident at 2 months of age but remained constant over the period during which the cells die. A decrease in rhodopsin density found in the outer segment may underlie the outer segment shortening but does not lead to rhodopsin accumulation in the inner segment. Our data argue against defects in rhodopsin transport or outer segment renewal as triggers of cell death in CHM.

Retinal imaging in inherited retinal diseases

Inherited retinal diseases (IRD) are a leading cause of blindness in the working age population. The advances in ocular genetics, retinal imaging and molecular biology, have conspired to create the ideal environment for establishing treatments for IRD, with the first approved gene therapy and the commencement of multiple therapy trials. The scope of this review is to familiarize clinicians and scientists with the current landscape of retinal imaging in IRD. Herein we present in a comprehensive and concise manner the imaging findings of: (I) macular dystrophies (MD) [Stargardt disease (ABCA4), X-linked retinoschisis (RS1), Best disease (BEST1), pattern dystrophy (PRPH2), Sorsby fundus dystrophy (TIMP3), and autosomal dominant drusen (EFEMP1)], (II) cone and cone-rod dystrophies (GUCA1A, PRPH2, ABCA4 and RPGR), (III) cone dysfunction syndromes [achromatopsia (CNGA3, CNGB3, PDE6C, PDE6H, GNAT2, ATF6], blue-cone monochromatism (OPN1LW/OPN1MW array), oligocone trichromacy, bradyopsia (RGS9/R9AP) and Bornholm eye disease (OPN1LW/OPN1MW), (IV) Leber congenital amaurosis (GUCY2D, CEP290, CRB1, RDH12, RPE65, TULP1, AIPL1 and NMNAT1), (V) rod-cone dystrophies [retinitis pigmentosa, enhanced S-Cone syndrome (NR2E3), Bietti crystalline corneoretinal dystrophy (CYP4V2)], (VI) rod dysfunction syndromes (congenital stationary night blindness, fundus albipunctatus (RDH5), Oguchi disease (SAG, GRK1), and (VII) chorioretinal dystrophies [choroideremia (CHM), gyrate atrophy (OAT)].

Cone Identification in Choroideremia: Repeatability, Reliability, and Automation Through Use of a Convolutional Neural Network

Purpose

Adaptive optics imaging has enabled the visualization of photoreceptors both in health and disease. However, there remains a need for automated accurate cone photoreceptor identification in images of disease. Here, we apply an open-source convolutional neural network (CNN) to automatically identify cones in images of choroideremia (CHM). We further compare the results to the repeatability and reliability of manual cone identifications in CHM.

Methods

We used split-detection adaptive optics scanning laser ophthalmoscopy to image the inner segment cone mosaic of 17 patients with CHM. Cones were manually identified twice by one experienced grader and once by two additional experienced graders in 204 regions of interest (ROIs). An open-source CNN either pre-trained on normal images or trained on CHM images automatically identified cones in the ROIs. True and false positive rates and Dice's coefficient were used to determine the agreement in cone locations between data sets. Interclass correlation coefficient was used to assess agreement in bound cone density.

Results

Intra- and intergrader agreement for cone density is high in CHM. CNN performance increased when it was trained on CHM images in comparison to normal, but had lower agreement than manual grading.

Conclusions

Manual cone identifications and cone density measurements are repeatable and reliable for images of CHM. CNNs show promise for automated cone selections, although additional improvements are needed to equal the accuracy of manual measurements.

Translational Relevance

These results are important for designing and interpreting longitudinal studies of cone mosaic metrics in disease progression or treatment intervention in CHM.

Role of Epithelial-Mesenchymal Transition in Retinal Pigment Epithelium Dysfunction

Retinal pigment epithelial (RPE) cells maintain the health and functional integrity of both photoreceptors and the choroidal vasculature. Loss of RPE differentiation has long been known to play a critical role in numerous retinal diseases, including inherited rod-cone degenerations, inherited macular degeneration, age-related macular degeneration, and proliferative vitreoretinopathy. Recent studies in post-mortem eyes have found upregulation of critical epithelial-mesenchymal transition (EMT) drivers such as TGF-β, Wnt, and Hippo. As RPE cells become less differentiated, they begin to exhibit the defining characteristics of mesenchymal cells, namely, the capacity to migrate and proliferate. A number of preclinical studies, including animal and cell culture experiments, also have shown that RPE cells undergo EMT. Taken together, these data suggest that RPE cells retain the reprogramming capacity to move along a continuum between polarized epithelial cells and mesenchymal cells. We propose that movement along this continuum toward a mesenchymal phenotype be defined as RPE Dysfunction. Potential mechanisms include impaired tight junctions, accumulation of misfolded proteins and dysregulation of several key pathways and molecules, such as TGF-β pathway, Wnt pathway, nicotinamide, microRNA 204/211 and extracellular vesicles. This review synthesizes the evidence implicating EMT of RPE cells in post-mortem eyes, animal studies, primary RPE, iPSC-RPE and ARPE-19 cell lines.

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.

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.

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.

A Case Study of Choroideremia and Choroideremia Carrier

Aim:

The aim of this case report was to report the clinical and genetic characteristics of choroideremia patient and a family member carrier.

Case report:

A comprehensive ophthalmologic examination, BCVA (best corrected visual acuity), fundus examination and photography, optical coherence tomography (OCT), OCT–angiography (OCTA), perimetry was conducted in choroideremia patient and a family member carrier. Clinical findings of choroidermia patient presented as significant atrophy of the choroid and retinal pigment epithelium (RPE) with the exception of a portion of preserved tissue in the macula. OCT showed foveal thickening with parafovoal RPE and fotoreceptor (FR) atrophy. OCTA revealed loss of choriocapillaris vasculature. Clinical diagnosis of CHM mutation was confirmed by multiplex ligation-dependent probe amplification assay (MLPA), followed by sequencing which revealed pathogen variance (c.1584_1587delTGTT). Clinical findings of carrier: small peripheral zones of atrophy and hyper pigmentation, without any symptoms or major visible changes on OCT or OCTA.

Conclusion:

Following new frontiers in gene therapy it is of curtail importance to diagnose patients correctly as well as confirm clinical diagnosis by genetic testing.

Statins in ophthalmology

Statins, 3-hydroxy-3-methyl-gutaryl coenzyme A reductase inhibitors, are a class of lipid-lowering drugs with anti-inflammatory, immunomodulatory, and vascular effects. Statins are increasingly being used in the treatment of a variety of medical conditions. We examine the actions of statins on the eye and its associated ophthalmic disorders. Statins can be synthetic or nonsynthetic, and their differentiating derivations may contribute to their varying cholesterol-lowering and pleiotropic effects. There is conflicting evidence on the ocular therapeutic and adverse effects of the statins. Statins may play a role in reducing the burden of dry eye, corneal ulcer scarring, thyroid-associated orbitopathy, glaucoma, uveitis and other associated ocular inflammatory states, cataract, proliferative vitreoretinopathy, diabetic retinopathy, macular degeneration, and choroidal melanoma. Topical preparations of statins can be formulated, thereby extending the range of ocular diseases that may be amenable to treatment. Statins have a relatively safe side effect profile, but rare and serious adverse reactions have been reported with their usage in ophthalmology, including myopathies and rhabdomyolysis with acute renal failure.

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.

Deep Scleral Exposure: A Degenerative Outcome of End-Stage Stargardt Disease

PURPOSE

To describe a distinct phenotypic outcome of outer retinal degeneration in a cohort of genetically confirmed patients with recessive Stargardt disease (STGD1).

DESIGN

Retrospective case series.

METHODS

Twelve patients, who were clinically diagnosed with STGD1 and exhibited a unique degenerative phenotype, were included in the study. Two disease-causing mutations were found in all patients by direct sequencing of the ABCA4 gene. Clinical characterization of patients were defined on fundus photographs, autofluorescence images (488-nm and 532-nm excitation), spectral-domain optical coherence tomography (SD-OCT), and full-field electroretinogram (ffERG) testing.

RESULTS

Mean age at initial presentation was 67.8 years and reported age of symptomatic onset was 14.1 years (mean disease duration = 53.8 years). Best-corrected visual acuity ranged from 20/400 to hand motion. All patients exhibited advanced degeneration across the posterior pole resulting in a reflectively pale, blonde fundus owing to unobstructed exposure of the underlying sclera. SD-OCT revealed complete loss of the outer retinal bands (external limiting membrane, ellipsoid zone, interdigitation zone, and retinal pigment epithelium) and choroidal layers. Scotopic and photopic waveforms on ffERG were nonrecordable or severely attenuated in 8 patients who were tested.

CONCLUSIONS

Widespread scleral exposure is a clinical outcome in a subset of STGD1 following a long duration of disease progression (∼50 years). The blonde fundus in such cases may exhibit phenotypic overlap and shared therapeutic implications with other aggressive chorioretinal dystrophies such as end-stage choroideremia, gyrate atrophy, or RPE65-Leber congenital amaurosis.

Patient-derived induced pluripotent stem cells for modelling genetic retinal dystrophies

The human retina is a highly complex tissue that makes up an integral part of our central nervous system. It is astonishing that our retina works seamlessly to provide one of our most critical senses, and it is equally devastating when a disease destroys a portion of the retina and robs people of their vision. After decades of research, scientists are beginning to understand retinal cells in a way that can benefit the millions of individuals suffering from inherited blindness. This understanding has come about in part with the ability to culture human embryonic stem cells and the innovation of induced pluripotent stem cells, which can be cultured from patients and used to model their disease. In this review, we highlight the successes of specific disease modelling studies and resulting molecular discoveries. The greatest strides in cellular modelling have come from mutations in genes with established and well-understood cellular functions in the context of the retina. We believe that the future of cellular modelling depends on emphasising reproducible production of retinal cell types, demonstrating functional rescue using site-specific programmable nucleases, and shifting towards unbiased screening using next generation sequencing.

SCLERAL PITS IN CHOROIDEREMIA: Implications for Retinal Gene Therapy

PURPOSE

We report a novel finding on spectral domain optical coherence tomography in patients with choroideremia, which we describe as scleral pits (SCPs).

METHODS

Cross-sectional observational case series of 36 patients with choroideremia, who underwent ophthalmic examination and multimodal imaging, including optical coherence tomography of the macula. Optical coherence tomography images were reviewed for SCP, which were defined as discrete tracts of hyporeflectivity that traverse the sclera with or without the involvement of Bruch membrane, retinal pigment epithelium, and retina. Unpaired two-tailed t-test with Welch correction was used for statistical analysis.

RESULTS

Of the 36 patients, 19 had SCP in at least one eye. Scleral pits were confined to areas of advanced chorioretinal degeneration and never involved the foveola. Type 1 SCP affected only the sclera, whereas Type 2 SCP also involved the Bruch membrane and the retinal pigment epithelium. Type 3 SCP additionally had a full-thickness retinal defect. Patients with SCP were significantly older (51 ± 2 vs. 33 ± 4 years; P < 0.05) and had lower best-corrected visual acuity (20/160 vs. 20/30 or 0.9 ± 0.2 vs. 0.2 ± 0.07 logarithm of the minimum angle of resolution; P < 0.05) than patients without SCP. Patients with SCP had a greater myopic refractive error compared with patients without SCP (-2.6 ± 0.5 vs. -0.3 ± 0.5D; P < 0.05), but there was no significant correlation between the number of SCPs with refraction. Short posterior ciliary arteries were observed to enter the eye through one Type 3 SCP.

CONCLUSION

Scleral pits are, to the best of our knowledge, a novel optical coherence tomography finding in advanced choroideremia that likely represents the abnormal juxtaposition of penetrating short posterior ciliary arteries with the retina.

Automated detection of preserved photoreceptor on optical coherence tomography in choroideremia based on machine learning

Optical coherence tomography (OCT) can demonstrate early deterioration of the photoreceptor integrity caused by inherited retinal degeneration diseases (IRDs). A machine learning method based on random forests was developed to automatically detect continuous areas of preserved ellipsoid zone structure (an easily recognizable part of the photoreceptors on OCT) in 16 eyes of patients with choroideremia (a type of IRD). Pseudopodial extensions protruding from the preserved ellipsoid zone areas are detected separately by a local active contour routine. The algorithm is implemented on en face images with minimum segmentation requirements, only needing delineation of the Bruch's membrane, thus evading the inaccuracies and technical challenges associated with automatic segmentation of the ellipsoid zone in eyes with severe retinal degeneration.

Automated detection of preserved photoreceptor on optical coherence tomography in choroideremia based on machine learning

Optical coherence tomography (OCT) can demonstrate early deterioration of the photoreceptor integrity caused by inherited retinal degeneration diseases (IRDs). A machine learning method based on random forests was developed to automatically detect continuous areas of preserved ellipsoid zone structure (an easily recognizable part of the photoreceptors on OCT) in 16 eyes of patients with choroideremia (a type of IRD). Pseudopodial extensions protruding from the preserved ellipsoid zone areas are detected separately by a local active contour routine. The algorithm is implemented on en face images with minimum segmentation requirements, only needing delineation of the Bruch's membrane, thus evading the inaccuracies and technical challenges associated with automatic segmentation of the ellipsoid zone in eyes with severe retinal degeneration.

Use of induced pluripotent stem cell models to probe the pathogenesis of Choroideremia and to develop a potential treatment

Choroideremia (CHM) is a rare monogenic, X-linked recessive inherited retinal degeneration resulting from mutations in the Rab Escort Protein-1 (REP1) encoding CHM gene. The primary retinal cell type leading to CHM is unknown. In this study, we explored the utility of induced pluripotent stem cell-derived models of retinal pigmented epithelium (iPSC-RPE) to study disease pathogenesis and a potential gene-based intervention in four different genetically distinct forms of CHM. A number of abnormal cell biologic, biochemical, and physiologic functions were identified in the CHM mutant cells. We then identified a recombinant adeno-associated virus (AAV) serotype, AAV7m8, that is optimal for both delivering transgenes to iPSC-RPEs as well as to appropriate target cells (RPE cells and rod photoreceptors) in the primate retina. To establish the proof of concept of AAV7m8 mediated CHM gene therapy, we developed AAV7m8.hCHM, which delivers the human CHM cDNA under control of CMV-enhanced chicken β-actin promoter (CßA). Delivery of AAV7m8.hCHM to CHM iPSC-RPEs restored protein prenylation, trafficking and phagocytosis. The results confirm that AAV-mediated delivery of the REP1-encoding gene can rescue defects in CHM iPSC-RPE regardless of the type of disease-causing mutation. The results also extend our understanding of mechanisms involved in the pathophysiology of choroideremia.

Novel mutation in the choroideremia gene and multi-Mendelian phenotypes in Spanish families

Aims

We aimed to accurately diagnose several retinitis pigmentosa (RP) patients with complex ocular phenotypes by combining massive sequencing genetic diagnosis and powerful clinical imaging techniques.

Methods

Whole-exome sequencing (WES) of selected patients from two RP families was undertaken. The variants identified were validated by Sanger sequencing and cosegregation analysis. Accurate clinical re-evaluation was performed using electrophysiological and visual field records as well as non-invasive imaging techniques, such as swept-source optical coherence tomography and fundus autofluorescence.

Results

The WES results highlighted one novel and one reported causative mutations in the X-linked choroideremia gene (CHM), which challenged the initial RP diagnosis. Subsequent clinical re-evaluation confirmed the choroideremia diagnosis. Carrier females showed different degrees of affectation, even between twin sisters, probably due to lyonization. A severe multi-Mendelian phenotype was associated with coincidental dominant pathogenic mutations in two additional genes: PAX6 and PDE6B.

Conclusions

Genetic diagnosis via massive sequencing is instrumental in identifying causative mutations in retinal dystrophies and additional genetic variants with an impact on the phenotype. Multi-Mendelian phenotypes previously ascribed to rare syndromes can thus be dissected and molecularly diagnosed. Overall, the combination of powerful genetic diagnosis and clinical non-invasive imaging techniques enables efficient management of patients and their prioritisation for gene-specific therapies.

Characterizing the Natural History of Visual Function in Choroideremia Using Microperimetry and Multimodal Retinal Imaging

Purpose

Centripetal retinal degeneration in choroideremia (CHM) leads to early visual field restriction and late central vision loss. The latter marks an acute decline in quality of life but visual prognostication remains challenging. We investigated visual function in CHM by correlating best-corrected visual acuity (BCVA), microperimetry and multimodal imaging.

Methods

Fifty-six consecutive CHM patients attending Oxford Eye Hospital were examined with BCVA, 10–2 microperimetry, optical coherence tomography, and fundus autofluorescence (AF). Microperimetry was repeated in 21 eyes and analyzed with Bland-Altman. Kaplan-Meier survival plots of eyes retaining 20/20 BCVA were created. Intereye symmetry was assessed.

Results

Microperimetry coefficient of repeatability was 1.45 dB. Survival analysis showed an indistinguishable pattern between eyes (median survival 39 years). Macular sensitivity showed a similar decline in right and left eyes, with half-lives of 13.6 years. Zonal analysis showed faster decline nasal to the fovea. Intereye symmetry was more consistent for microperimetry sensitivity (r = 0.95, P < 0.001) than BCVA (r = 0.42, P = 0.0006). Near normal foveal sensitivity was maintained when the fovea was at least 2500 μm from the advancing edge of AF.

Conclusions

BCVA is a marker of central degeneration and can provide valuable information about the position of the remaining retina as well as a measure of the impact on daily living. Microperimetry represents the global macular region. Both visual functions showed a high degree of intereye symmetry, particularly in early stages, indicating the fellow eye can provide a suitable control for assessing interventions to one eye. The findings may help to tailor visual prognosis and interpret outcomes of trials.

Genetic analysis and clinical phenotype of two Indian families with X-linked choroideremia

Purpose:

This study aims to describe the phenotype and genotype of two Indian families affected with X-linked choroideremia (CHM).

Materials and Methods:

In these two families, the affected individuals and unaffected family members underwent a comprehensive ophthalmic examination including an optical coherence tomography (OCT) and electroretinogram. Blood samples were collected from the families for genetic analysis. Next generation sequencing (NGS) was done using a panel of 184 genes, which covered previously associated genes with retinal dystrophies. Sequencing data were analyzed for the CHM, RPGR, and RP2 genes that have been implicated in CHM and X-linked retinitis pigmentosa (XLRP), respectively. The identified variants were confirmed by Sanger sequencing in available individuals and unrelated controls.

Results:

In two unrelated male patients, NGS analysis revealed a previously reported 3’-splice site change c.820-1G>C in the CHM gene in the first family and hemizygous mutation c.653G>C (p.Ser218X) in the second family. The asymptomatic family members were carriers for these mutations. Spectral domain-OCT showed loss of outer retina, preservation of the inner retina, and choroidal thinning in the affected males and retinal pigment epithelial changes in the asymptomatic carriers. The identified mutations were not present in 100 controls of Indian origin. There were no potential mutations found in XLRP-associated (RPGR and RP2) genes.

Conclusion:

This report describes the genotype and phenotype findings in patients with CHM from India. The identified genetic mutation leads to lack of Rab escort protein-1 (REP-1) or affects the production of a REP-1 protein that is likely to cause retinal abnormalities in patients.

A Qualitative and Quantitative Assessment of Fundus Autofluorescence Patterns in Patients With Choroideremia

Purpose

We set out to characterize the pattern of fundus autofluorescence (AF) loss in choroideremia (CHM) patients of varying ages and disease severity in order to determine the average rate of progression of this potential disease biomarker.

Methods

Fifty consecutive CHM patients (100 eyes) attending outpatient clinics at Oxford Eye Hospital underwent analysis with the Heidelberg OCT Spectralis with autofluorescence capabilities. The area of residual AF was traced using Heidelberg Eye Explorer. Bland-Altman analysis was used to calculate the coefficient of repeatability (CR). The degree of AF loss was correlated to different ages and the pattern of residual AF constructed into color-coded maps in order to gain insight into the mechanism of disease progression.

Results

The CR for measurement of AF area is <1%, indicating that a small change is likely to be significant. Correlation of patient age and area of residual AF produced a clinically relevant index of expected anatomic disease. Progression is 7.7% of the residual area each year (95% confidence intervals 7.0%–8.2%) and follows a logarithmic pattern with age (r = 0.95, P < 0.001). From this we derived the mean half-life of AF as 9 years. Qualitatively, the pattern of remaining AF centered on a point temporal to the fovea.

Conclusions

The area of residual AF in CHM can be measured reproducibly and shows a distinct pattern of loss. The measured residual area is inversely correlated to age. The ratio of the two variables may provide useful information regarding the rate of progression for any one individual at a given point in time.

Natural History of the Central Structural Abnormalities in Choroideremia: A Prospective Cross-Sectional Study

PURPOSE

To describe in detail the central retinal structure of a large group of patients with choroideremia (CHM).

DESIGN

A prospective, cross-sectional, descriptive study.

PARTICIPANTS

Patients (n = 97, age 6-71 years) with CHM and subjects with normal vision (n = 44; ages 10-50 years) were included.

METHODS

Subjects were examined with spectral-domain optical coherence tomography (SD OCT) and near-infrared reflectance imaging. Visual acuity (VA) was measured during their encounter or obtained from recent ophthalmic examinations. Visual thresholds were measured in a subset of patients (n = 24) with automated static perimetry within the central regions (±15°) examined with SD OCT.

MAIN OUTCOME MEASURES

Visual acuity and visual thresholds; total nuclear layer, inner nuclear layer (INL), and outer nuclear layer (ONL) thicknesses; and horizontal extent of the ONL and the photoreceptor outer segment (POS) interdigitation zone (IZ).

RESULTS

Earliest abnormalities in regions with normally appearing retinal pigment epithelium (RPE) were the loss of the POS and ellipsoid zone associated with rod dysfunction. Transition zones (TZs) from relatively preserved retina to severe ONL thinning and inner retinal thickening moved centripetally with age. Most patients (88%) retained VAs better than 20/40 until their fifth decade of life. The VA decline coincided with migration of the TZ near the foveal center. There were outer retinal tubulations in degenerated, nonatrophic retina in the majority (69%) of patients. In general, RPE abnormalities paralleled photoreceptor degeneration, although there were regions with detectable but abnormally thin ONL co-localizing with severe RPE depigmentation and choroidal thinning.

CONCLUSIONS

Abnormalities of the POS and rod dysfunction are the earliest central abnormalities observed in CHM. Foveal function is relatively preserved until the fifth decade of life. Migration of the TZs to the foveal center with foveal thinning and structural disorganization heralded central VA loss. The relationships established may help outline the eligibility criteria and outcome measures for clinical trials for CHM.