Pathogenic mechanisms and the prospect of gene therapy for choroideremia

Choroideremia presenting as vision loss secondary to choroidal neovascularization

BACKGROUND

Choroidal neovascularization (CNV) is a rare complication of choroideremia that occurs secondary to relative atrophy of the retinal pigment epithelium and eventual rupture of Bruch's membrane. The ideal management of CNV in choroideremia is unclear.

MATERIALS AND METHODS

Case report.

OBSERVATIONS

A 14-year-old male with no known ocular history presented to the eye emergency department complaining of a central scotoma in the right eye for 4 days. He had no past medical history and family history was unremarkable for known ocular disease. Visual acuity was 20/70 in the right eye and 20/30 in the left eye. Posterior segment exam revealed chorioretinal atrophy extending from the outer macula to the midperiphery in both eyes. There was CNV with associated subretinal hemorrhage in the right eye. Optical coherence tomography demonstrated the presence of CNV with subretinal fluid in the right eye and parafoveal outer retinal atrophy in both eyes. Genetic testing revealed a hemizygous exon 2 deletion on the CHM gene, pathogenic for choroideremia. The patient received a total of 3 injections 4 weeks apart followed by 1 injection 6 weeks later with resolution of the subretinal hemorrhage and reduction in CNV size with improvement in visual acuity to 20/20 at last follow-up exam.

CONCLUSIONS AND IMPORTANCE

Choroidal neovascularization is a rare cause of central vision loss in patients with choroideremia. In this report, we demonstrate a good functional and anatomic response to intravitreal bevacizumab in a 14-year-old patient with undiagnosed choroideremia who presented with CNV-induced central vision loss.

A Prospective, Observational, Noninterventional Clinical Study of Participants With Choroideremia: The NIGHT Study

PURPOSE

The NIGHT study aimed to assess the natural history of choroideremia (CHM), an X-linked inherited chorioretinal degenerative disease leading to blindness, and determine which outcomes would be the most sensitive for monitoring disease progression.

DESIGN

A prospective, observational, multicenter cohort study.

METHODS

Males aged ≥18 years with genetically confirmed CHM, visible active disease within the macular region, and best-corrected visual acuity (BCVA) ≥34 Early Treatment Diabetic Retinopathy Study (ETDRS) letters at baseline were assessed for 20 months. The primary outcome was the change in BCVA over time at Months 4, 8, 12, 16, and 20. A range of functional and anatomical secondary outcome measures were assessed up to Month 12, including retinal sensitivity, central ellipsoid zone (EZ) area, and total area of fundus autofluorescence (FAF). Additional ocular assessments for safety were performed.

RESULTS

A total of 220 participants completed the study. The mean BCVA was stable over 20 months. Most participants (81.4% in the worse eye and 77.8% in the better eye) had change from baseline > -5 ETDRS letters at Month 20. Interocular symmetry was low overall. Reductions from baseline to Month 12 were observed (worse eye, better eye) for retinal sensitivity (functional outcome; -0.68 dB, -0.48 dB), central EZ area (anatomical outcome; -0.276 mm2, -0.290 mm2), and total area of FAF (anatomical outcome; -0.605 mm2, -0.533 mm2). No assessment-related serious adverse events occurred.

CONCLUSIONS

Retinal sensitivity, central EZ area, and total area of FAF are more sensitive than BCVA in measuring the natural progression of CHM.

Subretinal timrepigene emparvovec in adult men with choroideremia: a randomized phase 3 trial

Choroideremia is a rare, X-linked retinal degeneration resulting in progressive vision loss. A randomized, masked, phase 3 clinical trial evaluated the safety and efficacy over 12 months of follow-up in adult males with choroideremia randomized to receive a high-dose (1.0 × 1011 vector genomes (vg); n = 69) or low-dose (1.0 × 1010 vg; n = 34) subretinal injection of the AAV2-vector-based gene therapy timrepigene emparvovec versus non-treated control (n = 66). Most treatment-emergent adverse events were mild or moderate. The trial did not meet its primary endpoint of best-corrected visual acuity (BCVA) improvement. In the primary endpoint analysis, three of 65 participants (5%) in the high-dose group, one of 34 (3%) participants in the low-dose group and zero of 62 (0%) participants in the control group had ≥15-letter Early Treatment Diabetic Retinopathy Study (ETDRS) improvement from baseline BCVA at 12 months (high dose, P = 0.245 versus control; low dose, P = 0.354 versus control). As the primary endpoint was not met, key secondary endpoints were not tested for significance. In a key secondary endpoint, nine of 65 (14%), six of 35 (18%) and one of 62 (2%) participants in the high-dose, low-dose and control groups, respectively, experienced ≥10-letter ETDRS improvement from baseline BCVA at 12 months. Potential opportunities to enhance future gene therapy studies for choroideremia include optimization of entry criteria (more preserved retinal area), surgical techniques and clinical endpoints. EudraCT registration: 2015-003958-41 .

Clinical and genetic findings in a Chinese cohort with choroideremia

OBJECTIVE

Choroideremia (CHM) is an X-linked chorioretinal dystrophy caused by variants in the CHM gene. The aim of this study was to report the clinical and genetic features of a cohort of affected males with CHM and establish the relationship between best correct visual acuity (BCVA) and age.

METHOD

Twenty-seven patients from 24 unrelated families underwent detailed ophthalmic examinations and comprehensive molecular genetic analysis. We combined the 27 patients in our own cohort with 68 Chinese patients from six previously reported studies to determine a transition age for BCVA rapid decline in 95 patients.

RESULTS

Twenty-three causal (9 novel) CHM variants were identified in the 27 patients, who had a mean age of 30.5 ± 17.4 years and a mean BCVA (LogMAR) of 0.61 ± 0.79. Patients at different disease stages showed different extents of retinal pigment epithelium (RPE) and choroid abnormalities. Central retinal optical coherence tomography (OCT) scanning revealed defects in the ellipsoid zone and RPE in all patients and outer retinal tubulations in 75%. The 95 patients had a mean age of 33.27 ± 16.27 years and an average (LogMAR) of 0.72 ± 0.82. The BCVA did not decline rapidly before age 25, but decreased at a mean rate of 0.037logMAR/year after that age.

CONCLUSIONS

Our results indicated Chinese patients with CHM variants have a younger transition age for rapid BCVA decline than previously reported for other ethnic groups. Central retinal OCT scanning can identify different abnormalities in the retinal structures, and these might be used as other parameters for monitoring disease progression in patients with CHM.

A Novel Hypothesis on Choroideremia-Manifesting Female Carriers: Could CHM In-Frame Variants Exert a Dominant Negative Effect? A Case Report

Choroideremia is an X-linked recessive condition presenting in males, with progressive degeneration of retinal and choroidal tissues leading to progressive visual loss. Its pathological mechanism is due to alterations in the CHM gene that encodes for REP1, a protein required for prenylation of Rab by the Rab geranylgeranyl transferase (RGGT). Even though female carriers are predicted to be not affected by the disease, a wide phenotypic spectrum ranging from mild to severe cases has been reported in women. The reason why Choroideremia manifests in female carriers remains elusive. While X chromosome inactivation (XCI) skewing has been proposed as a leading putative mechanism, emerging evidence has shown that CHM could variably escape from XCI. We described a family with an initial clinical suspicion of Retinitis Pigmentosa in which a novel CHM pathogenic splicing variant was found by exome sequencing. The variant, initially found in the 63-year-old female presenting with impaired visual acuity and severe retinal degeneration, segregated in the 31-year-old daughter and the 37-year-old son, both presenting with fundus anomalies. mRNA studies revealed a shorter in-frame CHM isoform lacking exon 10. Molecular modeling of the ternary REP1/Rab/RGGT protein complex predicted significant impairing of REP1/Rab binding without alteration of REP1/RGGT interaction. We suggest that, in our female cases, the biallelic expression of CHM may have led to the production of both the mutant and wild type REP1. The mutant isoform, sequestrating RGGT, could reduce its available amount for Rab prenylation, thus exerting a dominant-negative effect. If confirmed with further studies and in large cohorts of female carriers, the here proposed molecular mechanism could help to explain the complexity of manifestation of Choroideremia in females.

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.

Bilateral visual acuity decline in males with choroideremia: a pooled, cross-sectional meta-analysis

BACKGROUND

Choroideremia is a rare inherited retinal disease that leads to blindness. Visual acuity (VA) is a key outcome measure in choroideremia treatment studies, but VA decline rates change with age. An accurate understanding of the natural deterioration of VA in choroideremia is important to assess the treatment effect of new therapies in which VA is the primary outcome measure. We conducted a meta-analysis of data on individuals with choroideremia to determine the rate of VA deterioration between the better- and worse-seeing eye (BSE and WSE, respectively).

METHODS

Data were collected from the prospective Natural History of the Progression of Choroideremia (NIGHT) study (613 eyes, baseline data only), studies included in a recent meta-analysis, and studies identified in a targeted literature search performed on March 25, 2020, including individual best-corrected VA (BCVA) and age data in male individuals with choroideremia. Best-corrected VA decline rates (measured by logMAR units) by age and trends in BCVA decline rates in the BSE and WSE were evaluated.  RESULTS: Data from 1037 males (1602 eyes; mean age, 41.8 years) were included. Before and after an age cutoff of 33.8 years, BCVA decline rates for the WSE were 0.0086 and 0.0219 logMAR per year, respectively. Before and after an age cutoff of 39.1 years, BCVA decline rates for the BSE were 0.00001 and 0.0203 logMAR per year, respectively. Differences in absolute BCVA and decline rates increased between the 2 eyes until age ~ 40; thereafter, differences in absolute BCVA and decline rates were similar between eyes.

CONCLUSIONS

Using the largest choroideremia data set to date, this analysis demonstrates accelerated BCVA decline beginning between 30 and 40 years of age. Disparate interocular progression rates were observed before the transition age, with similar interocular progression rates after the transition age.

The Next Generation of Molecular and Cellular Therapeutics for Inherited Retinal Disease

Inherited retinal degenerations (IRDs) are a diverse group of conditions that are often characterized by the loss of photoreceptors and blindness. Recent innovations in molecular biology and genomics have allowed us to identify the causative defects behind these dystrophies and to design therapeutics that target specific mechanisms of retinal disease. Recently, the FDA approved the first in vivo gene therapy for one of these hereditary blinding conditions. Current clinical trials are exploring new therapies that could provide treatment for a growing number of retinal dystrophies. While the field has had early success with gene augmentation strategies for treating retinal disease based on loss-of-function mutations, many novel approaches hold the promise of offering therapies that span the full spectrum of causative mutations and mechanisms. Here, we provide a comprehensive review of the approaches currently in development including a discussion of retinal neuroprotection, gene therapies (gene augmentation, gene editing, RNA modification, optogenetics), and regenerative stem or precursor cell-based therapies. Our review focuses on technologies that are being developed for clinical translation or are in active clinical trials and discusses the advantages and limitations for each approach.

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

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

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.

Imaging in inherited retinal disorders

Inherited retinal diseases, which results from mutations in over 260 identified genes, affect more than 2 million people globally. The diseases mostly cause severe vision loss in young working population and have severe impact on social economic status of the population. Advances in retinal imaging techniques along with developments in gene identification and cell biology techniques have yielded to a better understanding of the genetic and biochemical mechanisms causing these diseases. Retinal imaging along with through ophthalmological examination is essential to make an accurate diagnosis, to decrease the burden of unneccessary anciliary tests and to select the potential patients that can get benefit from the gene treatment. The purpose of the review is to yield an update on inherited retinal diseases by highlighting microstructural changes in retina and to summarize the retinal changes detected by currently available multimodal imaging techniques.

CHOROIDEREMIA: Retinal Degeneration With an Unmet Need

PURPOSE

Choroideremia is an incurable, X-linked, recessive retinal dystrophy caused by loss of function mutations in the CHM gene. It is estimated to affect approximately 1 in 50,000 male patients. It is characterized by progressive degeneration of the retinal pigment epithelium, choroid, and photoreceptors, resulting in visual impairment and blindness. There is an unmet need in choroideremia, because currently, there are no approved treatments available for patients with the disease.

METHODS

We review the patient journey, societal impact, and emerging treatments for patients with choroideremia.

RESULTS

Its relative rarity and similarities with other retinal diseases in early years mean that diagnosis of choroideremia can often be delayed. Furthermore, its impact on affected individuals, and wider society, is also likely underestimated. AAV2-mediated gene therapy is an investigational treatment that aims to replace the faulty CHM gene. Early-phase studies reported potentially important visual acuity gains and maintenance of vision in some patients, and a large Phase 3 program is now underway.

CONCLUSION

Choroideremia is a disease with a significant unmet need. Interventions that can treat progression of the disease and improve visual and functional outcomes have the potential to reduce health care costs and enhance patient quality of life.

Fluorescence Lifetime Imaging Ophthalmoscopy (FLIO) in Patients with Choroideremia

Purpose

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

Methods

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

Results

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

Conclusions

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

Translational Relevance

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

Whole exome sequencing of a family revealed a novel variant in the CHM gene, c.22delG p.(Glu8Serfs*4), which co-segregated with choroideremia

Choroideremia is a complex form of blindness-causing retinal degeneration. The aim of the present study was to investigate the pathogenic variant and molecular etiology associated with choroideremia in a Chinese family. All available family members underwent detailed ophthalmological examinations. Whole exome sequencing, bioinformatics analysis, Sanger sequencing, and co-segregation analysis of family members were used to validate sequencing data and confirm the presence of the disease-causing gene variant. The proband was diagnosed with choroideremia on the basis of clinical manifestations. Whole exome sequencing showed that the proband had a hemizygous variant in the CHM gene, c.22delG p. (Glu8Serfs*4), which was confirmed by Sanger sequencing and found to co-segregate with choroideremia. The variant was classified as likely pathogenic and has not previously been described. These results expand the spectrum of variants in the CHM gene, thus potentially enriching the understanding of the molecular basis of choroideremia. Moreover, they may provide insight for future choroideremia diagnosis and gene therapy.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Genome Editing in Patient iPSCs Corrects the Most Prevalent USH2A Mutations and Reveals Intriguing Mutant mRNA Expression Profiles

Inherited retinal dystrophies (IRDs) are characterized by progressive photoreceptor degeneration and vision loss. Usher syndrome (USH) is a syndromic IRD characterized by retinitis pigmentosa (RP) and hearing loss. USH is clinically and genetically heterogeneous, and the most prevalent causative gene is USH2A. USH2A mutations also account for a large number of isolated autosomal recessive RP (arRP) cases. This high prevalence is due to two recurrent USH2A mutations, c.2276G>T and c.2299delG. Due to the large size of the USH2A cDNA, gene augmentation therapy is inaccessible. However, CRISPR/Cas9-mediated genome editing is a viable alternative. We used enhanced specificity Cas9 of Streptococcus pyogenes (eSpCas9) to successfully achieve seamless correction of the two most prevalent USH2A mutations in induced pluripotent stem cells (iPSCs) of patients with USH or arRP. Our results highlight features that promote high target efficacy and specificity of eSpCas9. Consistently, we did not identify any off-target mutagenesis in the corrected iPSCs, which also retained pluripotency and genetic stability. Furthermore, analysis of USH2A expression unexpectedly identified aberrant mRNA levels associated with the c.2276G>T and c.2299delG mutations that were reverted following correction. Taken together, our efficient CRISPR/Cas9-mediated strategy for USH2A mutation correction brings hope for a potential treatment for USH and arRP patients.

Crystals and Fatty Acid Abnormalities Are Not Present in Circulating Cells From Choroideremia Patients

Purpose

To confirm whether choroideremia (CHM) is a systemic disease characterized by blood lipid abnormalities and crystals found in, or associated with, circulating peripheral blood cells of patients.

Methods

Peripheral blood samples obtained from three subjects with confirmed mutations in the CHM gene and three age-matched normal controls were processed for transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Fatty acids from plasma of nine male CHM subjects were analyzed and compared to reference values for a sample from a Canadian population.

Results

Intracellular crystals were not observed in the cells from choroideremia-affected males. No crystals were found adherent to the external plasma membrane of red blood cells. Fatty acid profiles of patients were similar to reference values, with the exception of lower levels of nervonic acid.

Conclusions

This investigation failed to observe crystals previously reported in peripheral circulating blood cells derived from CHM subjects, and showed no significant fatty acid abnormalities, not supporting the view of CHM as a systemic disease.

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 Gene Therapy Phase 2 Clinical Trial: 24-Month Results

PURPOSE

To report the final results of a phase 2 high-dose gene therapy clinical trial in choroideremia.

METHODS

Design: Phase 2 clinical trial.

PARTICIPANTS

Six men (aged 32-72 years) with genetically-confirmed advanced choroideremia. Patients received subfoveal injection of AAV2-REP1 (10¹¹ genome particles in 0.1 mL) in the worse-sighted eye.

OUTCOME MEASURES

Primary measure was best-corrected visual acuity (BCVA) change from baseline in the treated eye compared to the untreated eye. Secondary endpoints included change from baseline in microperimetry, fundus autofluorescence, and spectral-domain optical coherence tomography (OCT). Safety evaluations included adverse events, viral shedding in body fluids, and vector antibody responses.

RESULTS

Baseline mean ETDRS BCVA was 65.3 ± 8.8 (SD, range 56-77, 20/32-20/80) letters in the treated eyes and 77.0 ± 4.2 (69-81, 20/25-20/40) letters in the untreated eyes. At 2 years, 1 treated eye improved by 10 letters and another by 5 letters, while 1 untreated eye improved by 4 letters. All other eyes were within 2 letters of baseline. Baseline microperimetry sensitivities in the treated eyes were poor (1.2 ± 2.1 (0, 5.1) dB) and showed no significant change. No serious adverse event occurred. Two patients developed an atrophic retinal hole in a nonfunctioning macular area where baseline OCT showed preexisting thinning. Intraoperative microscope-integrated OCT allowed proper subretinal injection with avoidance of excessive foveal stretching and macular hole formation.

CONCLUSIONS

Sustained improvement or maintenance of BCVA is achievable in choroideremia with high-dose AAV2-REP1, indicating BCVA is a viable primary outcome in advanced choroideremia. Choroideremia gene therapy delivered with intraoperative OCT has a good safety profile.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Clinical applications of retinal gene therapies

Retinal degenerative diseases are a major cause of blindness. Retinal gene therapy is a trail-blazer in the human gene therapy field, leading to the first FDA approved gene therapy product for a human genetic disease. The application of Clustered Regularly Interspaced Short Palindromic Repeat/Cas9 (CRISPR/Cas9)-mediated gene editing technology is transforming the delivery of gene therapy. We review the history, present, and future prospects of retinal gene therapy.

Guiding Lights in Genome Editing for Inherited Retinal Disorders: Implications for Gene and Cell Therapy

Inherited retinal dystrophies (IRDs) are a leading cause of visual impairment in the developing world. These conditions present an irreversible dysfunction or loss of neural retinal cells, which significantly impacts quality of life. Due to the anatomical accessibility and immunoprivileged status of the eye, ophthalmological research has been at the forefront of innovative and advanced gene- and cell-based therapies, both of which represent great potential as therapeutic treatments for IRD patients. However, due to a genetic and clinical heterogeneity, certain IRDs are not candidates for these approaches. New advances in the field of genome editing using Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) and CRISPR-associated protein (Cas) have provided an accurate and efficient way to edit the human genome and represent an appealing alternative for treating IRDs. We provide a brief update on current gene augmentation therapies for retinal dystrophies. Furthermore, we discuss recent advances in the field of genome editing and stem cell technologies, which together enable precise and personalized therapies for patients. Lastly, we highlight current technological limitations and barriers that need to be overcome before this technology can become a viable treatment option for patients.

Measurement and Reproducibility of Preserved Ellipsoid Zone Area and Preserved Retinal Pigment Epithelium Area in Eyes With Choroideremia

PURPOSE

To identify valid and reproducible methods for quantifying anatomic outcome measures for eyes with choroideremia (CHM) in clinical trials.

DESIGN

Reliability analysis study.

METHODS

In this multicenter study, patients with confirmed genetic diagnosis of CHM were enrolled. All cases underwent spectral-domain optical coherence tomography (SDOCT) and fundus autofluorescence (FAF) imaging. Two graders independently delineated boundaries of preserved autofluorescence (PAF) and preserved ellipsoid zone (EZ) on FAF and OCT images, respectively. The results of the 2 independent gradings of both FAF and OCT images were compared to assess the reproducibility of the grading methods.

RESULTS

A total of 148 eyes from 75 cases were included. In 21% of eyes PAF and in 43% of eyes preserved EZ had extended beyond the image capture area. After exclusion of these eyes and low-quality images, 114 FAF and 77 OCT images were graded. The mean PAF areas from 2 independent gradings were 3.720 ± 3.340 mm² and 3.692 ± 3.253 mm², respectively. Intraclass correlation coefficient (ICC) for these gradings was 0.996. The mean preserved EZ areas from 2 independent gradings were 2.746 ± 2.319 mm² and 2.858 ± 2.446 mm², respectively. ICC for these gradings was 0.991.

CONCLUSIONS

Quantifying preserved retinal pigment epithelium and EZ areas on FAF and OCT images, respectively, in CHM patients is highly reproducible. These variables would be potential anatomic outcome measures for CHM clinical trials and could be studied and tracked longitudinally in choroideremia.

Single-base substitutions in the CHM promoter as a cause of choroideremia

Although over 150 unique mutations affecting the coding sequence of CHM have been identified in patients with the X-linked chorioretinal disease choroideremia (CHM), no regulatory mutations have been reported, and indeed the promoter has not been defined. Here, we describe two independent families affected by CHM bearing a mutation outside the gene's coding region at position c.-98: C>A and C>T, which segregated with the disease. The male proband of family 1 was found to lack CHM mRNA and its gene product Rab escort protein 1, whereas whole-genome sequencing of an affected male in family 2 excluded the involvement of any other known retinal genes. Both mutations abrogated luciferase activity when inserted into a reporter construct, and by further employing the luciferase reporter system to assay sequences 5' to the gene, we identified the CHM promoter as the region encompassing nucleotides c.-119 to c.-76. These findings suggest that the CHM promoter region should be examined in patients with CHM who lack coding sequence mutations, and reveals, for the first time, features of the gene's regulation.

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.

Gene and cell-based therapies for inherited retinal disorders: An update

Retinal degenerations present a unique challenge as disease progression is irreversible and the retina has little regenerative potential. No current treatments for inherited retinal disease have the ability to reverse blindness, and current dietary supplement recommendations only delay disease progression with varied results. However, the retina is anatomically accessible and capable of being monitored at high resolution in vivo. This, in addition to the immune-privileged status of the eye, has put ocular disease at the forefront of advances in gene- and cell-based therapies. This review provides an update on gene therapies and randomized control trials for inherited retinal disease, including Leber congenital amaurosis, choroideremia, retinitis pigmentosa, Usher syndrome, X-linked retinoschisis, Leber hereditary optic neuropathy, and achromatopsia. New gene-modifying and cell-based strategies are also discussed. © 2016 Wiley Periodicals, Inc.

A Comprehensive Analysis of Choroideremia: From Genetic Characterization to Clinical Practice

Choroideremia (CHM) is a rare X-linked disease leading to progressive retinal degeneration resulting in blindness. The disorder is caused by mutations in the CHM gene encoding REP-1 protein, an essential component of the Rab geranylgeranyltransferase (GGTase) complex. In the present study, we evaluated a multi-technique analysis algorithm to describe the mutational spectrum identified in a large cohort of cases and further correlate CHM variants with phenotypic characteristics and biochemical defects of choroideremia patients. Molecular genetic testing led to the characterization of 36 out of 45 unrelated CHM families (80%), allowing the clinical reclassification of four CHM families. Haplotype reconstruction showed independent origins for the recurrent p.Arg293* and p.Lys178Argfs*5 mutations, suggesting the presence of hotspots in CHM, as well as the identification of two different unrelated events involving exon 9 deletion. No certain genotype-phenotype correlation could be established. Furthermore, all the patients´ fibroblasts analyzed presented significantly increased levels of unprenylated Rabs proteins compared to control cells; however, this was not related to the genotype. This research demonstrates the major potential of the algorithm proposed for diagnosis. Our data enhance the importance of establish a differential diagnosis with other retinal dystrophies, supporting the idea of an underestimated prevalence of choroideremia. Moreover, they suggested that the severity of the disorder cannot be exclusively explained by the genotype.