Pseudoxanthoma elasticum and retinitis pigmentosa in a patient with a novel mutation in the ABCC6 gene

BACKGROUND

Pseudoxanthoma elasticum (PXE) is an autosomal recessive condition caused by mutations in the ABCC6 gene. Ocular features include angioid streaks, peau d'orange fundus, and drusen. We report a novel ABCC6 mutation causing PXE in a patient with a mixed phenotype of PXE and retinitis pigmentosa (RP).

CASE

A 37-year-old female presented with decreased peripheral vision and nyctalopia. Ocular imaging revealed angioid streaks emanating from the optic nerve as well as peripheral pigmentary changes and bone spicules. Genetic testing revealed two mutations in ABCC6 in trans. No other mutation was identified.

CONCLUSION

We present a rare case with ocular findings of PXE and RP in a patient with a novel ABCC6 mutation. The patient presented both with peripheral pigmentary changes and angioid streaks. Further investigation into this novel mutation would be beneficial to determine if the mutation is involved in the RP phenotype.

Breaking bad news in ophthalmology: a pilot skills workshop for residents

OBJECTIVE

To design and implement a formal skills workshop for ophthalmology residents to practice breaking bad news.

METHODS

A 2-session workshop was developed for 7 ophthalmology residents at the University of Alberta based on a workshop published by Ohio State University. Residents discussed the SPIKES protocol for breaking bad news, practiced mock cases with standardized patients, and listened to shared experiences from patients who had received ocular diagnoses.

RESULTS

All the residents (n = 6; p = 0.03) at the University of Alberta reported an increase in confidence in 3 measures of an encounter in which they had to break bad news, one of which shared the significant improvement reported by the Ohio State group (n = 9; p = 0.01): setting realistic expectations without destroying hope. Standardized patients discussed their satisfaction with their case training and suggested the provision of eye models or printouts to enhance the realism in the examination rooms. The University of Alberta workshop results replicated those from Ohio State in that the SPIKES lecture and standardized patient session were ranked highly in efficacy (median, 4 of 5). The University of Alberta panel discussion was ranked lower than at Ohio State University, which may have resulted from 1 of 2 patient guest speakers being unexpectedly unable to attend.

CONCLUSION

The pilot Breaking Bad News Workshop was well received overall and may serve to inform future incorporation of soft skills development in a formal residency curriculum.

Overcoming the Challenges to Clinical Development of X-Linked Retinitis Pigmentosa Therapies: Proceedings of an Expert Panel

X-linked retinitis pigmentosa (XLRP) is a rare inherited retinal disease manifesting as impaired night vision and peripheral vision loss that progresses to legal blindness. Although several trials of ocular gene therapy for XLRP have been conducted or are in progress, there is currently no approved treatment. In July 2022, the Foundation Fighting Blindness convened an expert panel to examine relevant research and make recommendations for overcoming the challenges and capitalizing on the opportunities in conducting clinical trials of RPGR-targeted therapy for XLRP. Data presented concerned RPGR structure and mutation types known to cause XLRP, RPGR mutation-associated retinal phenotype diversity, patterns in genotype/phenotype relationships, disease onset and progression from natural history studies, and the various functional and structural tests used to monitor disease progression. Panel recommendations include considerations, such as genetic screening and other factors that can impact clinical trial inclusion criteria, the influence of age on defining and stratifying participant cohorts, the importance of conducting natural history studies early in clinical development programs, and the merits and drawbacks of available tests for measuring treatment outcomes. We recognize the need to work with regulators to adopt clinically meaningful end points that would best determine the efficacy of a trial. Given the promise of RPGR-targeted gene therapy for XLRP and the difficulties encountered in phase III clinical trials to date, we hope these recommendations will help speed progress to finding a cure.

Translational Relevance

Examination of relevant data and recommendations for the successful clinical development of gene therapies for RPGR-associated XLRP.

AAV2-Mediated Gene Therapy for Choroideremia: 5-Year Results and Alternate Anti-sense Oligonucleotide Therapy

PURPOSE

To assess the long-term safety and efficacy of AAV2-REP1 in choroideremia (CHM) patients, and to test a potential antisense oligonucleotide therapy for CHM.

DESIGN

Extended, prospective phase 1/2 clinical trial and laboratory investigation.

METHODS

Five patients who received a single subfoveal injection of AAV2-REP1 were studied. The long-term safety was evaluated by ophthalmic examination, spectral domain optical coherence tomography, and fundus autofluorescence (FAF) for up to 5 years. Functional and structural changes were determined by different test modalities. Four antisense oligonucleotides (ASOs) were designed to treat the CHM c.1245-521A>G mutation, which was present in 2 patients within this trial.

RESULTS

Subject P3 experienced a localized intraretinal immune response that resulted in a significant loss of preserved retinal pigment epithelium (RPE). P4 experienced an exacerbation of peripheral retinoschisis. P2 had a constant ≥15-letter best-corrected visual acuity (BCVA) gain in the treated eye, whereas P5 had ≥15-letter BCVA improvement once in the untreated eye. The preserved FAF areas declined more rapidly in the treated eyes compared to the untreated eyes (P = .043). A customized 25-mer ASO recovered 83.2% to 95.0% of the normal RNA and 57.5% of the normal protein in fibroblasts from 2 trial patients.

CONCLUSIONS

Intraretinal inflammation triggered by AAV2-REP1 subretinal injection stabilized after 2 years but resulted in permanent damage to the retinal structure. Long-term progression of the disease was seen in both treated and untreated eyes, casting doubt as to the effectiveness of this approach in late-stage CHM. Alternative approaches such as ASO may have a therapeutic effect in a subgroup of CHM patients.

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.

Whole exome sequencing reveals putatively novel associations in retinopathies and drusen formation

Inherited retinal dystrophies (IRDs) affect 1 in 3000 individuals worldwide and are genetically heterogeneous, with over 270 identified genes and loci; however, there are still many identified disorders with no current genetic etiology. Whole exome sequencing (WES) provides a hypothesis-free first examination of IRD patients in either a clinical or research setting to identify the genetic cause of disease. We present a study of IRD in ten families from Alberta, Canada, through the lens of novel gene discovery. We identify the genetic etiology of IRDs in three of the families to be variants in known disease-associated genes, previously missed by clinical investigations. In addition, we identify two potentially novel associations: LRP1 in early-onset drusen formation and UBE2U in a multi-system condition presenting with retinoschisis, cataracts, learning disabilities, and developmental delay. We also describe interesting results in our unsolved cases to provide further information to other investigators of these blinding conditions.

Validating Ellipsoid Zone Area Measurement With Multimodal Imaging in Choroideremia

Purpose

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

Methods

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

Results

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

Conclusions

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

Translational Relevance

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

PEX6 Mutations in Peroxisomal Biogenesis Disorders: An Usher Syndrome Mimic

PURPOSE

Peroxisomal biogenesis disorders (PBDs) represent a spectrum of conditions that result in vision loss, sensorineural hearing loss, neurologic dysfunction, and other abnormalities resulting from aberrant peroxisomal function caused by mutations in PEX genes. With no treatments currently available, we sought to investigate the disease mechanism in a patient with a PBD caused by defects in PEX6 and to probe whether overexpression of PEX6 could restore peroxisome function and potentially offer therapeutic benefit.

DESIGN

Laboratory-based study.

PARTICIPANTS

A 12-year-old boy sought treatment with hearing loss and retinopathy. After negative results in an Usher syndrome panel, targeted genetic testing revealed compound heterozygous mutations in PEX6. These included a 14-nucleotide deletion (c.802_815del: p.(Asp268Cysfs∗8)) and a milder missense variant (c.35T→C:(p.Phe12Ser)).

METHODS

Patient-derived skin fibroblasts were cultured, and a PEX6 knockout cell line was developed using clustered regularly interspaced short palindromic repeats and Cas9 technology in HEK293T cells to emulate a more severe disease phenotype. Immunoblot analysis of whole cell lysates was performed to assess peroxisome number. Immunofluorescence studies used antibodies against components of the peroxisomal protein import pathway to interrogate the effects of mutations in PEX6 on protein trafficking.

MAIN OUTCOME MEASURES

Primary outcome measures were peroxisome abundance and matrix protein import.

RESULTS

Peroxisome number was not significantly different between control fibroblasts and patient fibroblasts; however, fewer peroxisomes were observed in PEX6 knockout cells compared with wild-type cells (P = 0.04). Analysis by immunofluorescent microscopy showed significantly impaired peroxisomal targeting signal 1- and peroxisomal targeting signal 2-mediated matrix protein import in both patient fibroblasts and PEX6 knockout cells. Overexpressing PEX6 resulted in improved matrix protein import in PEX6 knockout cells.

CONCLUSIONS

Mutations in PEX6 were responsible for combined hearing loss and retinopathy in our patient. The primary peroxisomal defect in our patient's skin fibroblasts was impaired peroxisomal protein import as opposed to reduction in the number of peroxisomes. Genetic strategies that introduce wild-type PEX6 into cells deficient in PEX6 protein show promise in restoring peroxisome function. Future studies of patient-specific induced pluripotent stem cell-derived retinal pigment epithelium cells may clarify the role of PEX6 in the retina and the potential for gene therapy in these patients.

A homozygous POC1B variant causes recessive cone-rod dystrophy

Purpose: To report a case of initial cone dystrophy that advanced to a cone-rod dystrophy with homozygous variants in the POC1B gene.Methods: Retinal structure and visual function assessments were performed using fundoscopy, spectral-domain optical coherence tomography, full field electroretinography, semi-kinetic perimetry, and Ishihara plate testing. A DNA sample was collected and sent for diagnostic molecular genetic testing with a cone-rod dystrophy panel.Results: Clinical examination and electroretinography confirmed a clinical diagnosis of cone dystrophy. Molecular genetic testing revealed homozygous variants in POC1B (c.1355 G > A, p.(Arg452Gln)). Follow-up three years later showed progression to a cone-rod dystrophy.Conclusion: Our case describes an ophthalmological phenotype associated with a homozygous POC1B missense variant and provides clinical support for variant classification.

Zebrafish Models of Photoreceptor Dysfunction and Degeneration

Zebrafish are an instrumental system for the generation of photoreceptor degeneration models, which can be utilized to determine underlying causes of photoreceptor dysfunction and death, and for the analysis of potential therapeutic compounds, as well as the characterization of regenerative responses. We review the wealth of information from existing zebrafish models of photoreceptor disease, specifically as they relate to currently accepted taxonomic classes of human rod and cone disease. We also highlight that rich, detailed information can be derived from studying photoreceptor development, structure, and function, including behavioural assessments and in vivo imaging of zebrafish. Zebrafish models are available for a diversity of photoreceptor diseases, including cone dystrophies, which are challenging to recapitulate in nocturnal mammalian systems. Newly discovered models of photoreceptor disease and drusenoid deposit formation may not only provide important insights into pathogenesis of disease, but also potential therapeutic approaches. Zebrafish have already shown their use in providing pre-clinical data prior to testing genetic therapies in clinical trials, such as antisense oligonucleotide therapy for Usher syndrome.

Severe retinal degeneration in a patient with Canavan disease

Background: Canavan disease is an autosomal recessive, neurodegenerative disorder caused by mutations in ASPA, a gene encoding the enzyme aspartoacylase. Patients present with macrocephaly, developmental delay, hypotonia, vision impairment and accumulation of N-acetylaspartic acid. Progressive white matter changes occur in the central nervous system. The disorder is often fatal in early childhood, but milder forms exist. Materials and methods: Case report. Results: We present the case of a 31-year-old male with mild/juvenile Canavan disease who had severe vision loss due to a retinal degeneration resembling retinitis pigmentosa. Prior to this case, vision loss in Canavan disease had been attributed to optic atrophy based on fundoscopic evidence of optic nerve pallor. Investigations for an alternative cause for our patient's retinal degeneration were non-revealing. Conclusion: We wonder if retinal degeneration may not have been previously recognized as a feature of Canavan disease. We highlight findings from animal models of Canavan disease to further support the association between Canavan disease and retinal degeneration.

A diagnostic approach to syndromic retinal dystrophies with intellectual disability

Inherited retinal dystrophies are a group of monogenic disorders that, as a whole, contribute significantly to the burden of ocular disease in both pediatric and adult patients. In their syndromic forms, retinal dystrophies can be observed in association with intellectual disability, frequently alongside other systemic manifestations. There are now over 80 genes implicated in syndromic retinal dystrophies with intellectual disability. Identifying and accurately characterizing these disorders allows the clinician to narrow the differential diagnosis, evaluate for relevant associated features, arrive at a timely and accurate diagnosis, and address both sight-threatening ocular manifestations and morbidity-causing systemic manifestations. The co-occurrence of retinal dystrophy and intellectual disability in an individual can be challenging to investigate, diagnose, and counsel given the considerable phenotypic and genotypic heterogeneity that exists within this broad group of disorders. We performed a review of the current literature and propose an algorithm to facilitate the evaluation, and clinical and mechanistic classification, of these individuals.

Improved electroretinographic responses following dietary intervention in a patient with Refsum disease

Refsum disease is a rare inherited metabolic disorder arising from a defect in peroxisomal metabolism. Patients lack the functional enzyme phytanoyl-CoA hydroxylase, resulting in perturbed alpha oxidation of fatty acids. Phytanic acid accumulates in nervous and adipose tissue and leads to several disease phenotypes including early-onset retinal degeneration, hearing loss, peripheral neuropathy, anosmia, and cerebellar ataxia, among others. Currently, restricting dietary phytanic acid is the only means of altering the chronic sequelae and the disease course. While dietary intervention has been demonstrated to improve peripheral neuropathy, ichthyosis, and ataxia, there have been no reports of improved retinal function in patients with Refsum disease. We describe the case of a 51-year-old patient with molecularly and biochemically confirmed Refsum disease who underwent electroretinography before and after beginning a phytanic acid-restricted diet. His post-intervention 30 Hz flicker electroretinogram demonstrated significantly improved waveform amplitudes and implicit times, suggesting improved retinal function. Thus, we propose that the possibility exists for some visual recovery in these patients and we highlight the utility of performing standardized electroretinography to assess treatment response in Refsum disease.

Ocular Gene Therapy with Adeno-associated Virus Vectors: Current Outlook for Patients and Researchers

In this "Perspective", we discuss ocular gene therapy - the patient's perspective, the various strategies of gene replacement and gene editing, the place of adeno-associated virus vectors, routes of delivery to the eye and the remaining question - "why does immunity continue to limit efficacy?" Through the coordinated efforts of patients, researchers, granting agencies and industry, and after many years of pre-clinical studies, biochemical, cellular, and animal models, we are seeing clinical trials emerge for many previously untreatable heritable ocular disorders. The pathway to therapies has been led by the successful treatment of the RPE65 form of Leber congenital amaurosis with LUXTURNA TM . In some cases, immune reactions to the vectors continue to occur, limiting efficacy. The underlying mechanisms of inflammation require further study, and new vectors need to be designed that limit the triggers of immunity. Researchers studying ocular gene therapies and clinicians enrolling patients in clinical trials must recognize the current limitations of these therapies to properly manage expectations and avoid disappointment, but we believe that gene therapies are well on their way to successful, widespread utilization to treat heritable ocular disorders.

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.

Visual Field Progression in Retinitis Pigmentosa

Purpose

To retrospectively study the rate of visual field (VF) progression in patients with retinitis pigmentosa (RP) as it relates to different targets and inheritance patterns.

Methods

A total of 275 kinetic VF tests were collected from 52 subjects with RP over a period of up to 29 years (mean, 12 years). The VF areas of Goldmann targets V4e, III4e, and I4e were calculated using Photoshop. Differences in the rate of VF loss among different targets and inheritance patterns were compared.

Results

There was a significant interocular correlation in both visual acuity (VA) (R2 = 0.739, P < 0.001) and VF area (R2 = 0.815, P < 0.001). The annual rates of decline in VF area for V4e, III4e, and I4e targets were 7.5%, 10.7%, and 12.5%, respectively (all P < 0.001). All of the rates were significantly different from each other (P < 0.001). The mean rate of VF loss was 10.3% (P = 0.009) for autosomal recessive, 2.7% (P = 0.215) for autosomal dominant, and 7.2% (P = 0.009) for X-linked patterns of inheritance. However, the differences among them were not statistically significant (P > 0.05). Based on VF, survival analysis indicated that our patients failed the vision standard for driving and reached legal blindness at the median ages of 37 and 55 years, respectively.

Conclusions

The rate of VF loss varies among targets in patients with RP. Fifty percent of patients are not qualified to drive by the age of 37 and become legally blind by the age of 55. These results can be useful for counseling patients with RP as to their potential rate of VF decline.

Diffuse Pigmented Lesions in the Outer Retina: An Unusual Fundus Appearance

Purpose:

This report describes and provides a differential diagnosis for a patient with unusual bilateral retinal pigmented lesions.

Methods:

A 40-year-old woman was found to have multiple flat, gray lesions scattered across her fundi, becoming larger and more confluent toward the periphery. There were small drusenlike deposits in her foveae. The hyperpigmented lesions demonstrated hypoautofluorescence with thickening of the retinal pigment epithelium and disruption of the overlying layers on optical coherence tomography (OCT). Full-field electroretinography revealed generalized reduced a- and b-wave amplitudes.

Results:

Chest x-ray, breast ultrasound, mammography, and pelvic ultrasound findings were negative for malignant etiologic factors. Panel testing results for hereditary retinal dystrophy were negative.

Conclusions:

Although the clinical and OCT appearance of the lesions is similar to congenital grouped pigmentation, the symmetric and bilateral nature of ocular findings coupled with electroretinographic changes suggest a possible retinal dystrophy. This case adds to the phenotypic diversity of pigmented fundus lesions.

A novel SVA retrotransposon insertion in the CHM gene results in loss of REP-1 causing choroideremia

BACKGROUND

Choroideremia is an X-linked retinal disease characterized by progressive atrophy of the choroid and retinal pigment epithelium caused by mutations in the CHM gene. SVA (SINE-R/VNTR/Alu) elements are a type of non-autonomous retrotransposon that occasionally self-replicate, reinsert randomly into a gene, and cause disease. Intragenic SVA insertions have been reported as the mechanism underlying a number of diseases including a syndromic form of retinal dystrophy, but have never been found in CHM.

MATERIALS AND METHODS

Here we identified and characterized a novel hemizygous SVA insertion, c.97_98inSVA (p.Arg33insSVA), in exon 2 of CHM in a male choroideremia patient. The SVA insertion's impact was evaluated by establishing a patient-derived lymphoblastoid cell line as a source of RNA for mRNA analysis of the CHM transcript, and protein for immunoblot analysis of Rab Escort Protein 1 (REP-1).

RESULTS

Immunoblot analysis revealed the absence of REP-1 protein, while a smaller than expected PCR product was amplified from cDNA. Sequencing of this PCR product showed skipping of exon 2, denoted r.50_116del. Ophthalmic examination including psychophysical tests, visual electrophysiology, and fundus imaging showed the patient's phenotype was consistent with severe early manifestations of choroideremia.

CONCLUSIONS

This case is the first report of a SVA insertion in the CHM gene causing choroideremia.

Perspectives on Gene Therapy: Choroideremia Represents a Challenging Model for the Treatment of Other Inherited Retinal Degenerations

Purpose

To report combined viewpoints on ocular gene therapy from a select group of clinician scientists and a patient advocacy group.

Methods

With the support of Randy Wheelock and Dr. Chris Moen from the Choroideremia Research Foundation (CRF), a special interest group at the 2019 Annual meeting of the Association for Research in Vision and Ophthalmology in Vancouver, Canada, shared their knowledge, experience, concepts, and ideas and provided a forum to discuss therapeutic strategies for the treatment of inherited retinal disorders, using experience in choroideremia (CHM) as a model.

Results

A member of the CRF presented the patient perspective and role in clinical trials. Five clinician scientists presented reasons for limited long-term visual improvement in many gene therapy trials, including challenges with dose, incomplete understanding of photoreceptor metabolism, vector delivery, inflammation, and identification of patients likely to benefit from treatment.

Conclusions

The shared experience of the five clinician scientists indicates that the results of ocular gene therapy for choroideremia have been less successful than for RPE65-related Leber congenital amaurosis. Improvement in vector delivery and developing a better understanding of gene expression in target tissues, treatment dose and side effects, and inflammation, as well as identifying patients who are most likely to benefit without suffering excessive risk, are necessary to advance the development of effective therapies for inherited retinal degenerations.

Translational Relevance

Additional long-term data are required to determine if ocular gene therapy will be sufficient to alter natural progression in choroideremia. Combination therapies may have to be considered, as well as alternative vectors that minimize risk.

The Canadian Rare Diseases Models and Mechanisms (RDMM) Network: Connecting Understudied Genes to Model Organisms

Advances in genomics have transformed our ability to identify the genetic causes of rare diseases (RDs), yet we have a limited understanding of the mechanistic roles of most genes in health and disease. When a novel RD gene is first discovered, there is minimal insight into its biological function, the pathogenic mechanisms of disease-causing variants, and how therapy might be approached. To address this gap, the Canadian Rare Diseases Models and Mechanisms (RDMM) Network was established to connect clinicians discovering new disease genes with Canadian scientists able to study equivalent genes and pathways in model organisms (MOs). The Network is built around a registry of more than 500 Canadian MO scientists, representing expertise for over 7,500 human genes. RDMM uses a committee process to identify and evaluate clinician-MO scientist collaborations and approve 25,000 Canadian dollars in catalyst funding. To date, we have made 85 clinician-MO scientist connections and funded 105 projects. These collaborations help confirm variant pathogenicity and unravel the molecular mechanisms of RD, and also test novel therapies and lead to long-term collaborations. To expand the impact and reach of this model, we made the RDMM Registry open-source, portable, and customizable, and we freely share our committee structures and processes. We are currently working with emerging networks in Europe, Australia, and Japan to link international RDMM networks and registries and enable matches across borders. We will continue to create meaningful collaborations, generate knowledge, and advance RD research locally and globally for the benefit of patients and families living with RD.

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.

An analysis of strabismus reoperations in Northern Alberta, Canada from 1995 to 2015

OBJECTIVE

To report the reoperation rate in a large group of pediatric and adult strabismus patients over a 21-year period in Northern Alberta, Canada.

METHODS

A retrospective review of 6177 strabismus surgeries from July 1995 to June 2015 on 5125 pediatric and adult patients was conducted to determine the reoperation rate at a single major referral centre. A set of guidelines was implemented in November 2014 recommending delaying reintervention for at least 12 weeks from the initial surgery, with specific exceptions.

RESULTS

The historical strabismus reoperation rate over a 21-year period was 15.7%. Of those surgeries requiring reoperation, 77.7% required only 1 reoperation, 17.1% required 2 reoperations, 3.1% required 3 reoperations, and 2.1% required 4 or more reoperations. The mean time between surgeries for patients undergoing reoperation was 2.3 years and the median time was 1.0 years.

CONCLUSIONS

Our study provides insight into the strabismus reoperation rate and the number of subsequent surgeries performed for patients over a 21-year period. Although preoperative ocular alignment, comorbidities, and the status of the operative eye modify the probability of reoperation, our results from a large cohort of patients provide an impression of the rate of reoperation and may be of benefit in the preoperative counseling of patients. Furthermore, we highlight the scarcity of guidelines for the appropriate timing of reoperation. The implementation of specific guidelines may encourage future investigation into trends in reoperation over time and promote ways to avoid unnecessary surgeries, lower health care costs to stakeholders, and ultimately improve patient care.

Macular spatial distribution of preserved autofluorescence in patients with choroideremia

BACKGROUND/AIMS

To better understand the pattern of degeneration progression in cases with choroideremia.

METHODS

A cohort of genotypically confirmed choroideremia cases who underwent optical coherence tomography (OCT) and fundus autofluorescence (FAF) imaging was studied. Using HEYEX review software, the foveal centre was marked on FAF images under guidance of corresponding OCT images, followed by application of an ETDRS grid. The boundaries of preserved autofluorescence (AF) were manually segmented in each individual ETDRS subfield. The regional distribution of preserved AF was assessed by comparing its area among the various subfields.

RESULTS

A total of 168 eyes from 84 choroideremia cases were enrolled. There was a statistically significant difference in the amount of preserved AF area between inner subfields as determined by one-way analysis of variance (F (3,668)=9.997, p<0.001) and also between outer subfields (F (3,668)=8.348, p<0.001). A Tukey posthoc test revealed that the preserved AF area in the nasal subfields in both the inner and outer subfields was significantly smaller compared with analogue subfields.

CONCLUSION

The asymmetric spatial distribution of preserved AF in choroideremia (corresponding to the stellate shaped nature of these regions) suggests that the progression of degeneration has directional preference.

Two-Year Results After AAV2-Mediated Gene Therapy for Choroideremia: The Alberta Experience

PURPOSE

To assess the safety of a recombinant adeno-associated viral vector expressing REP1 (rAAV2.REP1) in choroideremia subjects.

METHODS

Design: Phase I clinical trial.

PARTICIPANTS

Six adult male subjects, 30-42 years of age, with genetically confirmed choroideremia (CHM) were enrolled. The eye with the worse vision, for all subjects, received a single subfoveal injection of 0.1 mL rAAV2.REP1 containing 10¹¹ genome particles. Subjects were followed up for 2 years thereafter.

OUTCOME MEASURES

The primary outcome measure was safety, determined by the number of ocular and systemic adverse events assessed by ophthalmic examination, spectral-domain optical coherence tomography (SD-OCT), and short-wavelength autofluorescence (FAF). Secondary outcome measures were the change from baseline in best-corrected visual acuity (BCVA) in the treated eye compared to the untreated eye, changes in visual function using microperimetry, and the area of retinal pigment epithelium (RPE) preservation by FAF.

RESULTS

One subject had an 8-ETDRS-letter BCVA loss from baseline measured at 24 months, while 1 subject had a ≥15-letter BCVA gain. A similar improvement was noted in the untreated eye of another subject throughout the follow-up period. Microperimetry sensitivity showed no improvement or significant change up to 2 years after vector administration. The area of preserved RPE as measured by FAF was noted to decline at a similar rate between the treated and untreated eyes. One subject experienced a serious adverse event: a localized intraretinal immune response, resulting in marked decline in visual function and loss of SD-OCT outer retinal structures.

CONCLUSIONS

One serious adverse event was experienced in 6 subjects treated with a subfoveal injection of AAV2.REP1. The area of remaining functional RPE in the treated eye and untreated eye declined at the same rate over a 2-year period. Fundus autofluorescence area is a remarkably predictive biomarker and objective outcome measure for future studies of ocular gene therapy in CHM subjects.

American Journal of Ophthalmology Contributions to Ophthalmic Genetics

PURPOSE

To review the contributions to ophthalmic genetics through the American Journal of Ophthalmology (AJO).

DESIGN

Perspective.

METHODS

A literature search to retrieve original articles, letters, editorials, and published lectures from 1966 to 2017, providing a 50-year review. Titles were excluded that gave no reference to genetics or that presented findings related to a nongenetic ocular condition.

RESULTS

From a search of the Scopus database, 719 articles were ascertained. Of these, 115 were excluded because the title did not reference a genetic condition or have a focus on genetic factors; 4 were excluded because they described animal phenotypes (1966-1967); and 4 were excluded owing to having received no citations up to and including 2015. The highest number of citations was 283 times for a single article on familial aggregation in age-related macular degeneration. The Web of Science database yielded 771 articles; of these, 118 were excluded owing to not reporting human genetic studies; 55 received no citations. The highest number of citations was 307 for a single article, a 1991 paper on Leber hereditary optic neuropathy.

CONCLUSIONS

The Journal's contributions to our understanding of the heritability of human ocular traits have been broad and deep, with international reach. The development of new techniques fostered new concepts and new approaches to rapidly expand the number of known single gene disorders with a defined molecular genetic cause. Reports on Mendelian and complex traits in the AJO abound, along with 6 Edward Jackson Memorial Lectures on retinal dystrophies, Leber congenital amaurosis, age-related macular degeneration, and glaucoma.

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.

Microperimetry as an Outcome Measure in Choroideremia Trials: Reproducibility and Beyond

PURPOSE

To determine test-retest repeatability of microperimetry testing (MP) in choroideremia (CHM) subjects using standard and personalized stimulus grids.

METHODS

Fifteen CHM subjects (28 eyes) underwent consecutive repeat examinations with the Macular Integrity Assessment (MAIA) microperimeter using a standard (10°) and a customized macular grid adapted to individual macular pathology. Repeatability of standard-grid mean (MS) and point-wise (PWS) sensitivity was determined and compared with age-matched controls (seven eyes), with PWS separately analyzed for loci within and outside the border of degeneration. Interpolated volumetric indices were used to estimate repeatability of customized grids and compare their performance to standard grids.

RESULTS

Test-retest measures of standard-grid MS yielded higher coefficients of variation (CV) in CHM subjects compared with controls (0.09 vs. 0.02). Volumetric indices from customized grids improved repeatability by driving CV values to 0.05 and close to 0.02 for region-of-interest (ROI) analysis. Variability of PWS was significantly higher in CHM, especially at the border of degeneration (10.68 vs. 4.74 dB at the central retina, P < 0.001).

CONCLUSIONS

Microperimetry testing in CHM shows high test-retest variation at the border of degeneration, which influences repeatability of MS measures. Volumetric measures from customized grids can improve reliability of both global and regional sensitivity assessment. Nevertheless, inherent test-retest variation of individual points needs to be taken into account when assessing potential functional decline and/or disease progression.

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.

Analysis of a large choroideremia dataset does not suggest a preference for inclusion of certain genotypes in future trials of gene therapy

Background

Choroideremia (CHM) is an X‐linked degeneration of the retinal pigment epithelium, photoreceptors, and choroid, which causes nyctalopia and progressive constriction of visual fields leading to blindness. The CHM gene encodes Rab escort protein 1 (REP‐1). In this work, we reviewed the phenotypes and genotypes of affected males with the purpose of understanding the functional effects of CHM mutations and their relationship with the phenotypes.

Methods

A retrospective review of 128 affected males was performed analyzing the onset of symptoms, visual acuity, and visual fields with respect to their mutations in the CHM gene.

Results

In rank order, reflecting data from this report, the most common mutations found in the CHM gene were nonsense mutations (41%), exon deletions (37%), and splice sites (14%) associated with a loss of functional protein. In the pool of 106 CHM mutations, we discovered four novel missense mutations (c.238C>T; p.L80F, c.819G>T; p.Q273H, c.1327A>G; p.M443V, and c.1370C>T; p.L457P) predicted to be severe changes affecting protein stability and folding with the effect similar to that of other types of mutations. No significant genotype–phenotype correlation was found with respect to the onset of nyctalopia, the onset of other visual symptoms, visual acuity, or width of visual fields.

Conclusion

There is no evidence to support exclusion of CHM patients from clinical trials based on their genotypes or any potential genotype–phenotype correlations.

Choroideremia research: Report and perspectives on the second international scientific symposium for choroideremia

PURPOSE

To discuss progress in research on choroideremia (CHM) and related retinopathies with special emphasis on gene therapy approaches.

METHODS

Biomedical and clinical researchers from across the world as well as representatives of the social science research community were convened to the 2nd International Scientific Symposium for Choroideremia in Denver, Colorado in June 2014 to enhance our understanding of CHM and accelerate the translation of research to clinical application for the benefit of those affected by CHM.

RESULTS

Pre-clinical research using cell and animal models continues to further our understanding in the pathogenesis of CHM as well as to demonstrate proof-of-concept for gene transfer strategies. With the advent of modern imaging technology, better outcome measures are being defined for upcoming clinical trials. Results from the first gene therapy trial in CHM show promise, with sustained visual improvement over 6 months post-treatment. Current and next-generation gene transfer approaches may make targeted vector delivery possible in the future for CHM and other inherited retinal diseases.

CONCLUSIONS

While no accepted therapies exist for CHM, promising approaches using viral-vectored gene therapy and cell therapies are entering clinical trials for eye diseases, with gene therapy trials underway for CHM.

Communicating the promise for ocular gene therapies: challenges and recommendations

PURPOSE

To identify challenges and pose solutions for communications about ocular gene therapy between patients and clinicians as clinical research progresses.

DESIGN

Literature review with recommendations.

METHODS

Literature review of science communication best practices to inform recommendations for patient-clinician discussions about ocular gene therapy.

RESULTS

Clinicians need to employ communications about ocular gene therapy that are both attentive to patient priorities and concerns and responsive to other sources of information, including overly positive news media and the Internet. Coverage often conflates research with therapy-clinical trials are experimental and are not risk free. If proven safe and efficacious, gene therapy may present a treatment but not a cure for patients who have already experienced vision loss. Clinicians can assist patients by providing realistic estimates for lengthy clinical development timelines and positioning current research within models of clinical translation. This enables patients to weigh future therapeutic options when making current disease management decisions.

CONCLUSIONS

Ocular gene therapy clinical trials are raising hopes for treating a myriad of hereditary retinopathies, but most such therapies are many years in the future. Clinicians should be prepared to counter overly positive messaging, found in news media and on the Internet, with optimism tempered by evidence to support the ethical translation of gene therapy and other novel biotherapeutics.

Pathogenic mechanisms and the prospect of gene therapy for choroideremia

INTRODUCTION

Choroideremia is a rare, X-linked disorder recognized by its specific ocular phenotype as a progressive degenerative retinopathy resulting in blindness. New therapeutic approaches, primarily based on genetic mechanisms, have emerged that aim to prevent the progressive vision loss.

AREAS COVERED

This article will review the research that has progressed incrementally over the past two decades from mapping to gene discovery, uncovering the presumed mechanisms triggering the retinopathy to preclinical testing of potential therapies.

EXPERT OPINION

While still in an evaluative phase, the introduction of gene replacement as a potential therapy has been greeted with great enthusiasm by patients, advocacy groups and the medical community.

Bilateral uveitis and Usher syndrome: a case report

Introduction

Usher syndrome is a genetically heterogeneous condition and represents the most common cause of inherited combined vision and hearing loss. Deficits manifest as sensorineural hearing loss that typically develops at a young age and retinitis pigmentosa that can lead to peripheral vision loss and night blindness. As a result, this syndrome can have a significant impact on a patient’s quality of life.

Previous studies have described an association between Usher syndrome and Fuchs’ heterochromic iridocyclitis, a form of non-granulomatous uveitis that generally presents in a unilateral manner. We present a rare finding of bilateral uveitis and, to the best of our knowledge, the first report of granulomatous uveitis as a feature in a patient with Usher syndrome.

Case presentation

A 45-year-old Caucasian woman with a known history of retinitis pigmentosa presented to our clinic with suspected Usher syndrome, given her report of long-standing hearing loss. Aside from a mild loss in visual acuity, our patient was otherwise asymptomatic. Visual field testing, audiology and electroretinography findings supported the diagnosis of Usher syndrome. With slit lamp examination she was found to have bilateral keratic precipitates, with large, greasy-white, mutton-fat keratic precipitates on the endothelial surface of her left eye. A thorough work-up that included blood tests and imaging was negative for an alternative cause of her uveitis.

Conclusion

We present a rare finding of bilateral uveitis and what we believe to be the first reported instance of mutton-fat keratic precipitates and granulomatous uveitis as a feature in a patient with Usher syndrome. By identifying atypical presentations of the disease, we hope to contribute to the range of ophthalmic conditions that may be seen in association with Usher syndrome.

Mutations in PNPLA6 are linked to photoreceptor degeneration and various forms of childhood blindness

Blindness due to retinal degeneration affects millions of people worldwide, but many disease-causing mutations remain unknown. PNPLA6 encodes the patatin-like phospholipase domain containing protein 6, also known as neuropathy target esterase (NTE), which is the target of toxic organophosphates that induce human paralysis due to severe axonopathy of large neurons. Mutations in PNPLA6 also cause human spastic paraplegia characterized by motor neuron degeneration. Here we identify PNPLA6 mutations in childhood blindness in seven families with retinal degeneration, including Leber congenital amaurosis and Oliver McFarlane syndrome. PNPLA6 localizes mostly at the inner segment plasma membrane in photoreceptors and mutations in Drosophila PNPLA6 lead to photoreceptor cell death. We also report that lysophosphatidylcholine and lysophosphatidic acid levels are elevated in mutant Drosophila. These findings show a role for PNPLA6 in photoreceptor survival and identify phospholipid metabolism as a potential therapeutic target for some forms of blindness.

Molecular genetic diagnostic techniques in choroideremia

PURPOSE

To optimize and streamline molecular genetics techniques in diagnosing choroideremia (CHM).

METHODS

PCR primers were designed for exons 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, and 15 of the CHM gene. Each PCR protocol was optimized so that all exons could be amplified with the same component ratio and PCR conditions. Sense and antisense primers were tested for their ability to be used as sequencing primers. Fibroblast cells were cultured, and an immunoblot analysis was performed to detect the presence or absence of Rab escort protein 1 (REP-1) in a suspected CHM patient sample when no mutation was detected with sequencing. Multiplex ligation-dependent probe amplification (MLPA) of the CHM gene was performed and used to detect deletions and duplications in affected males and female carriers. RNA analysis using cDNA was used to detect the presence or absence of the CHM transcript and to search for splice defects.

RESULTS

The newly designed PCR primers allow for more efficient PCR preparation and sequencing to detect point mutations in affected males and female carriers. Immunoblot successfully detects the absence of REP-1 in a CHM patient. MLPA identifies deletions and duplications spanning multiple exons in the CHM gene. RNA analysis aids in detecting splice variants.

CONCLUSIONS

The development of new molecular biology techniques and ongoing optimization of existing methods allows for an improved integrated approach to confirm CHM diagnosis and carrier status in consideration of patient family history and available patient sample materials. CHM can be confirmed with an immunoblot assay. To detect the molecular cause of CHM, an examination of the genomic DNA or the mRNA must be performed. Presymptomatic carriers with no identifiable fundus signs can be identified only through molecular analysis of genomic DNA or through quantitative assays.

High-resolution images of retinal structure in patients with choroideremia

PURPOSE

To study retinal structure in choroideremia patients and carriers using high-resolution imaging techniques.

METHODS

Subjects from four families (six female carriers and five affected males) with choroideremia (CHM) were characterized with best-corrected visual acuity (BCVA), kinetic and static perimetry, full-field electroretinography, and fundus autofluorescence (FAF). High-resolution macular images were obtained with adaptive optics scanning laser ophthalmoscopy (AOSLO) and spectral domain optical coherence tomography (SD-OCT). Coding regions of the CHM gene were sequenced.

RESULTS

Molecular analysis of the CHM gene identified a deletion of exons 9 to 15 in family A, a splice site mutation at position 79+1 of exon 1 in family B, deletion of exons 6 to 8 in family C, and a substitution at position 106 causing a premature stop in family D. BCVA ranged from 20/16 to 20/63 in carriers and from 20/25 to 5/63 in affected males. FAF showed abnormalities in all subjects. SD-OCT showed outer retinal layer loss, outer retinal tubulations at the margin of outer retinal loss, and inner retinal microcysts. Patchy cone loss was present in two symptomatic carriers. In two affected males, cone mosaics were disrupted with increased cone spacing near the fovea but more normal cone spacing near the edge of atrophy.

CONCLUSIONS

High-resolution retinal images in CHM carriers and affected males demonstrated RPE and photoreceptor cell degeneration. As both RPE and photoreceptor cells were affected, these cell types may degenerate simultaneously in CHM. These findings provide insight into the effect of CHM mutations on macular retinal structure, with implications for the development of treatments for CHM. (ClinicalTrials.gov number, NCT00254605.).