Jasleen K. Jolly

Visual Acuity after Retinal Gene Therapy for Choroideremia

In this study, the subfoveal injection of a gene-therapy vector carrying nonmutated CHM, the gene that, when mutated, causes a form of blindness called choroideremia, was followed by an improvement in visual acuity in two of six patients at 3.5 years after injection.

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

Purpose To evaluate the relationships between RPE, photoreceptor, and choroidal degeneration in choroideremia. Methods Enhanced-depth imaging optical coherence tomography (EDI-OCT), scanning laser ophthalmoscopy (SLO), and autofluorescence (AF) were performed on 39 patients (78 eyes) with choroideremia. The edges of surviving outer retina on OCT and residual AF were aligned. The distribution of outer retinal tubulations was mapped over a range of ages (16–71 years), and comparison made between pre- and postsubretinal gene therapy. Subfoveal choroidal thickness (SFCT) was compared between 23 choroideremia patients (42 eyes) and 20 age- and refraction-matched male controls (40 eyes). Results The edges of RPE AF aligned with a reduction in outer nuclear layer thickness (Spearmans rho = 0.9992). Correlation was also found between the quality of AF and integrity of ellipsoid zone within islands of surviving retina. Tubulations existed in 71 of 78 (91%) eyes with choroideremia and remained stable following gene therapy. Subfoveal choroidal thickness was reduced at baseline in choroideremia (179.7 ± 17.2 μm) compared with controls (302.0 ± 4.8 μm; P < 0.0001), but did not undergo significant thinning until end-stage retinal degeneration (43.1 ± 6.5 μm). Conclusions The data suggest that RPE loss is the primary cause of photoreceptor degeneration in choroideremia. The choroid is thinner than controls from early stages, in keeping with a mild developmental defect. Photoreceptors appear to lose outer segments following loss of underlying RPE and form tubulations at the edges of degeneration. The preservation of tubulations over time and after subretinal injection would be consistent with these structures maintaining attachment to the inner retina and hence being potentially light responsive (ClinicalTrials.gov, NCT01461213).

The Spectrum of CHM Gene Mutations in Choroideremia and Their Relationship to Clinical Phenotype.

Purpose We report the underlying genotype and explore possible genotypic-phenotypic correlations in a large cohort of choroideremia patients. Methods We studied prospectively a cohort of 79 patients diagnosed within a tertiary referral service for patients with retinal dystrophies. Phenotypic evaluation consisted of clinical examination, including visual acuity and residual retinal area by fundus autofluorescence (FAF). Genotype was established by sequencing. We also investigated whether particular genotypes were associated with more severe phenotypes by performing analysis of covariance (ANCOVA), with visual acuity and FAF as the dependent variables and age as the covariant. Results A total of 74 (94%) of patients in our cohort had causative mutations by sequencing, the majority of which were anticipated to be null. Of these, 35 (47%) had insertions and deletions, 13 (18%) had mutations predicted to affect splicing, and 26 (35%) had single point mutations. In the latter case, 13 of 21 (62%) pedigrees with single point mutations were C to T transitions at C-phosphate-G (CpG) dinucleotides. These mutations were spread across 5 of only 24 CpG dinucleotides in the entire CHM cDNA. Furthermore, these 5 locations are the only sites at which C to T transitions result in a stop codon. No clear evidence was found for genotype–phenotype correlation except in the instance of a patient with a large deletion involving neighbouring sequences. Conclusions In patients with a diagnosis of choroideremia made by a specialty service, there is a high likelihood of establishing a genetic diagnosis. The majority of causative mutations appear to be null and, therefore, may benefit from gene replacement therapy. A disproportionate number of single point mutations observed were C to T transitions, consistent with the evolutionary decay of CpG dinucleotides through methylation and subsequent deamination. Hence, the development of choroideremia in such patients may represent the unwanted consequence of human evolution; de novo mutations are predicted to arise at these sites in future generations. (ClinicalTrials.gov number, NCT01461213.)

Structural and Functional Recovery Following Limited Iatrogenic Macular Detachment for Retinal Gene Therapy

Importance The early decline and recovery of retinal structure and function following iatrogenic macular detachment for retinal gene therapy is not well characterized in those with relatively preserved central visual function. Here, the recovery of retinal structure and function over the first month following iatrogenic retinal detachment for the delivery of adeno-associated viral vector encoding Rab Escort Protein 1 is described as a part of gene therapy for choroideremia. Objective To study changes in both retinal structure and function during the first month following iatrogenic macular detachment surgery. Design, Setting, and Participants This prospective interocularly controlled study was conducted between February 1 and December 31, 2015. Treatment consisted of a subretinal injection of 0.1 mL of a gene therapy solution containing 1 × 1011 viral particles performed unilaterally. The participants were 5 males, aged 23 to 71 years, with a clinical and genetic diagnosis of choroideremia. Main Outcomes and Measures Retinal structure and function were assessed at baseline, 1 week, and 1 month using optical coherence tomography, logMAR visual acuity, microperimetry, the Farnsworth-Munsell (FM) 100-hue test, and the Rayleigh match. Results Five white male patients aged 23 to 71 years underwent unilateral subretinal gene therapy for genetically confirmed choroidermeia. Optical coherence tomographic images demonstrated a complete resolution of the resulting iatrogenic retinal detachment by 1 week in all 5 patients. At 1 month, the mean (SE) change in central foveal thickness was +9.6 (7.2) &mgr;m in treated eyes and +8.8 (12.6) &mgr;m in control eyes. The mean (SE) change in visual acuity was +5.4 (3.3) letters in treated eyes and +0.8 (3.1) letters in control eyes. At 1 month, the mean (SE) threshold sensitivity changes were −1.2 (2.1) dB in treated eyes and −1.0 (1.2) dB in control eyes. Color discrimination at the FM 100-hue changed little at 1 month (mean [SE] change in C-index, −0.2 [0.4] in treated eyes and 0.1 [0.2] in control eyes). Rayleigh matches in 1 patient were consistent with a diagnosis of pseudoprotanomaly, suggesting decreased effective optical density of the cone photopigments. Conclusions and Relevance Retinal structural recovery—as assessed by optical coherence tomography—occurs soon after iatrogenic detachment. Similarly, visual acuity recovers or improves within 1 month of the procedure and may not be accompanied by improvements in threshold sensitivity or color discrimination. Changes in color matching in 1 patient suggest decreased optical density of the cone photopigments in the early postoperative period.

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.

Retinal Degeneration in Choroideremia follows an Exponential Decay Function

Fundus autofluorescence (AF) arises from lipofuscin, which is derived from retinoid byproducts of the visual cycle and accumulates within retinal pigment epithelial cells. Alterations in AF pattern are seen in a wide range of retinal degenerations. Choroideremia is an X-linked retinal dystrophy caused by loss-of-function mutations within the CHM gene, encoding Rab escort protein-1. It is uniquely characterized by a central “island” of residual AF that undergoes gradual shrinkage with disease progression. The decrease in AF area is correlated precisely with loss of overlying photoreceptors, leading to progressive visual field restriction and blindness around the fifth decade. Retinal gene replacement therapy using an adeno-associated viral vector could potentially slow down or stop disease progression in choroideremia. Although visual acuity may be improved by gene therapy, it is affected relatively late in the disease; therefore, the area of residual AF may provide an alternative anatomic biomarker for monitoring progression at earlier stages. A previous cross-sectional study suggested an exponential decrease in AF area with age in choroideremia. However, longitudinal data on natural disease progression is lacking. For instance, it is uncertain whether individuals progressed at different rates depending on genetic, epigenetic, or environmental factors, and whether the rate of progression varied between early and late stages of the disease.

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.

Effects of pupil dilation on MAIA microperimetry.

Macular Integrity Assessment microperimetry assesses macular sensitivity to projected point light sources and maps eye movements to assess fixation stability. Although microperimetry is gaining prominence as an assessment tool in clinical and research settings, there is no consensus on whether it should be performed before or after pupil dilation. No studies to date have examined the effect of pupil dilation on results. The aim of this project was to elucidate the effect of pupil dilation on microperimetry outcomes.

A Novel Method for Quantitative Serial Autofluorescence Analysis in Retinitis Pigmentosa Using Image Characteristics

Purpose Identifying potential biomarkers for disease progression in retinitis pigmentosa (RP) is highly relevant now that gene therapy and other treatments are in clinical trial. Here we report a novel technique for analysis of short-wavelength autofluorescence (AF) imaging to quantify defined regions of AF in RP patients. Methods Fifty-five–degree AF images were acquired from 12 participants with RP over a 12-month period. Of these, five were identified as having a hyperfluorescent annulus. A standard Cartesian coordinate system was superimposed on images with the fovea as the origin and eight bisecting lines traversing the center at 45 degrees to each other. Spatial extraction software was programmed to highlight pixels corresponding to varying degrees of percentile fluorescence such that the parafoveal AF ring was mapped. Distance between the fovea and midpoint of the AF ring was measured. Percentage of low luminance areas was utilized as a measure of atrophy. Results The hyperfluorescent ring was most accurately mapped using the 70th percentile of fluorescence. Both the AF ring and peripheral hypofluorescence showed robust repeatability at all time points noted (P = 0.93). Conclusions Both a hypofluorescent ring and retinal pigment epithelium atrophy were present on a significant proportion of RP patients and were consistently mapped over a 12-month period. There is potential extrapolation of this methodology to wide-field imaging as well as other retinal dystrophies. This anatomical change may provide a useful anatomical biomarker for assessing treatment end points in RP. Translational Relevance Spatial extraction software can be a valuable tool in the assessment of ophthalmic imaging data.

Functional Defects in Color Vision in Patients With Choroideremia.

PURPOSE To characterize defects in color vision in patients with choroideremia. DESIGN Prospective cohort study. METHODS Thirty patients with choroideremia (41 eyes) and 10 age-matched male controls (19 eyes) with visual acuity of ≥6/36 attending outpatient clinics in Oxford Eye Hospital underwent color vision testing with the Farnsworth-Munsell 100 hue test, visual acuity testing, and autofluorescence imaging. To exclude changes caused by degeneration of the fovea, a subgroup of 14 patients with a visual acuity ≥6/6 was analyzed. Calculated color vision total error scores were compared between the groups and related to a range of factors using a random-effects model. RESULTS Mean color vision total error scores were 120 (95% confidence interval [CI] 92, 156) in the ≥6/6 choroideremia group, 206 (95% CI 161, 266) in the <6/6 visual acuity choroideremia group, and 47 (95% CI 32, 69) in the control group. Covariate analysis showed a significant difference in color vision total error score between the groups (P < .001 between each group). CONCLUSIONS Patients with choroideremia have a functional defect in color vision compared with age-matched controls. The color vision defect deteriorates as the degeneration encroaches on the fovea. The presence of an early functional defect in color vision provides a useful biomarker against which to assess successful gene transfer in gene therapy trials.