PHENOTYPING CHOROIDEREMIA AND ITS CARRIER STATE WITH MULTIMODAL IMAGING TECHNIQUES

Exploring the impact of Choroideremia on women with phenotypic and/or genotypic evidence of disease: insights from a global survey

INTRODUCTION

Choroideremia (CHM) is an X-linked inherited retinal disease mostly affecting males. However, women with phenotypic and/or genotypic evidence of CHM may develop degenerative visual disability with advancing age. Our objective was to determine the visual impacts of phenotypic and/or genotypic evidence of CHM in women and its associated psychosocial burden and influence on activities of daily living (ADLs).

METHODS

We conducted an international cross-sectional survey from April to December 2022 using an e-questionnaire distributed through not-for-profit stakeholder organizations and social media plat-forms.

RESULTS

With a total of 55 respondents (n = 55), most women with phenotypic and/or genotypic evidence of CHM (76%) reported a change in their visual acuity. When assessing its impact on ADLs, Pearson's correlation coefficient showed a negative correlation between driving (p = 0.046) and mobility capabil-ities (0.046) with the respondent's age. More than half of women reported being afraid, anxious, and stressed, with women below the age of 50 years old reporting a significantly higher level of distress and hopelessness (p = 0.003), anxiety (p = 0.00007), issues with relaxing (p = 0.025), and negative personal thoughts (p = 0.042).

CONCLUSION

Overall, this survey outlines both physical and psychological burden of being a woman with phenotypic and/or genotypic evidence of CHM. Given the limited clinical research in females affected by CHM, this patient-centered survey is a crucial advocacy tool for these individuals.

The Use of Induced Pluripotent Stem Cells as a Model for Developmental Eye Disorders

Approximately one-third of childhood blindness is attributed to developmental eye disorders, of which 80% have a genetic cause. Eye morphogenesis is tightly regulated by a highly conserved network of transcription factors when disrupted by genetic mutations can result in severe ocular malformation. Human-induced pluripotent stem cells (hiPSCs) are an attractive tool to study early eye development as they are more physiologically relevant than animal models, can be patient-specific and their use does not elicit the ethical concerns associated with human embryonic stem cells. The generation of self-organizing hiPSC-derived optic cups is a major advancement to understanding mechanisms of ocular development and disease. Their development in vitro has been found to mirror that of the human eye and these early organoids have been used to effectively model microphthalmia caused by a VSX2 variant. hiPSC-derived optic cups, retina, and cornea organoids are powerful tools for future modeling of disease phenotypes and will enable a greater understanding of the pathophysiology of many other developmental eye disorders. These models will also provide an effective platform for identifying molecular therapeutic targets and for future clinical applications.

Optical Coherence Tomography Angiography (OCT-A) in Choroideremia (CHM) carriers

Purposes: To explore OCT-A abnormalities in CHM carriersMethods: CHM carriers and age-matched controls were consecutively enrolled at the Eye Clinic in Florence. All patients underwent a complete ophthalmic examination, fundus photography, fundus autofluorescence (FAF) and OCT examinations. OCT-A images of the superficial capillary plexus (SCP), deep capillary plexus (DCP) and choriocapillaris slab (CC) were acquired and analyzed using ImageJ software to detect and quantify vascular density.Results: Six patients (12 eyes) and 8 age-matched controls (16 eyes) were included in our study. The mean age was 45.5 ± 16.3 years (range 15-61) for the CHM carriers and 46.6 ± 12.2 (range 18-54) for controls. All CHM carriers showed fundus abnormalities. The detected mean central retinal thickness (CRT) (220 ± 18.34 vs 227 ± 15.46; p = .342) and choroidal central thickness (CCT) (271 ± 54.28 vs 275 ± 38.36; p = .760) did not differ between the carrier and the control group, respectively. Quantitative analysis of the inner retinal vasculature disclosed no significant difference of both SCP (p = .437) and DCP (p = .859) vessel density compared to the control group. Of note, a mild reduction on the vascular flow of the CC could be detected in the carrier group compared to the control group (78.896 ± 13.972 vs 80.008 ± 10.862; p = .045).Conclusions: OCT-A allows us to underline the role of the retinal pigment epithelium in the CHM pathophysiology. Central inner retinal and choriocapillaris vascularization were preserved although the RPE was always involved in the CHM carrier: this could support a secondary role of vascular impairment in the natural history of the disease.

Insights into Retinal Development Using Live Imaging in Female Carriers of Choroideremia

Lineage tracing can provide key insights into the development of tissues, such as the retina. Yet it is not possible to manipulate human cells during embryogenesis. The authors observed a distinct phenotype in female carriers of X-linked disorders, in particular, carriers of choroideremia caused by mutations in CHM, encoding Rab escort protein-1. The authors found that X chromosome inactivation provides a method for retinal lineage tracing in human patients. Live imaging of female carriers displays a developmental pattern that is different within the peripheral retina compared with the posterior retina and provides important insights into the development and migration of retinal cells. [Ophthalmic Surg Lasers Imaging Retina. 2019;50:e158-e162.].

Toward the Mutational Landscape of Autosomal Dominant Retinitis Pigmentosa: A Comprehensive Analysis of 258 Spanish Families

Purpose

To provide a comprehensive overview of the molecular basis of autosomal dominant retinitis pigmentosa (adRP) in Spanish families. Thus, we established the molecular characterization rate, gene prevalence, and mutational spectrum in the largest European cohort reported to date.

Methods

A total of 258 unrelated Spanish families with a clinical diagnosis of RP and suspected autosomal dominant inheritance were included. Clinical diagnosis was based on complete ophthalmologic examination and family history. Retrospective and prospective analysis of Spanish adRP families was carried out using a combined strategy consisting of classic genetic techniques and next-generation sequencing (NGS) for single-nucleotide variants and copy number variation (CNV) screening.

Results

Overall, 60% of our families were genetically solved. Interestingly, 3.1% of the cohort carried pathogenic CNVs. Disease-causing variants were found in an autosomal dominant gene in 55% of the families; however, X-linked and autosomal recessive forms were also identified in 3% and 2%, respectively. Four genes (RHO, PRPF31, RP1, and PRPH2) explained up to 62% of the solved families. Missense changes were most frequently found in adRP-associated genes; however, CNVs represented a relevant disease cause in PRPF31- and CRX-associated forms.

Conclusions

Implementation of NGS technologies in the adRP study clearly increased the diagnostic yield compared with classic approaches. Our study outcome expands the spectrum of disease-causing variants, provides accurate data on mutation gene prevalence, and highlights the implication of CNVs as important contributors to adRP etiology.

CHOROIDEREMIA ASSOCIATED WITH A NOVEL SYNONYMOUS MUTATION IN GENE ENCODING REP-1

PURPOSE

To report a novel synonymous mutation in CHM and the associated phenotype in an affected man and carrier mother.

METHODS

Case report.

RESULTS

A 34-year-old man with a long history of progressive night blindness and visual field constriction was diagnosed with choroideremia based on ocular examination and multimodal retinal imaging. Extensive chorioretinal degeneration was noted on spectral domain optical coherence tomography and fundus autofluorescence imaging. Candidate CHM gene sequencing revealed a hemizygous c.1359C>T, p.(S453S) variant. This variant was heterozygous in the mother of the proband who exhibited the classic carrier phenotype of choroideremia on fundus autofluorescence imaging.

CONCLUSION

A novel c.1359C>T, p.(S453S) variant in CHM is the first-identified synonymous mutation associated with disease manifestation in an affected man and carrier phenotype in a heterozygous mother.

Caring for Hereditary Childhood Retinal Blindness

Inherited retinal diseases (IRDs) are a major cause of incurable familial blindness in the Western world. In the pediatric population, IRDs are a major contributor to the 19 million children worldwide with visual impairment. Unfortunately, the road to the correct diagnosis is often complicated in the pediatric population, as typical diagnostic tools such as fundus examination, electrodiagnostic studies, and other imaging modalities may be difficult to perform in the pediatric patient. In this review, we describe the most significant IRDs with onset during the pediatric years (ie, before the age of 18). We describe the pathogenesis, clinical presentation, and potential treatment of these diseases. In addition, we advocate the use of a pedigree (family medical history), electroretinography, and genetic testing as the 3 most crucial tools for the correct diagnosis of IRDs in the pediatric population.

Phenotypic expansion and progression of SPATA7-associated retinitis pigmentosa

PURPOSE

To report an unusual phenotype of retinitis pigmentosa (RP) caused by compound heterozygous mutations in SPATA7, and describe the progression over a two year follow-up period.

METHODS

Retrospective case study.

RESULTS

A 63-year-old man with a long history of nyctalopia, progressive visual field constriction, and a recent subacute decrease in visual acuity of the left eye presented for evaluation of a suspected retinal degeneration. Multimodal retinal imaging and functional assessment with full-field electroretinogram suggested a severe rod-cone dysfunction masquerading as a choroideremia-like phenotype. A vitreous opacity was found to explain recent changes in the left eye and a 25-guage vitrectomy and membrane peel was performed, yielding no change in visual acuity. Whole-exome sequencing revealed compound heterozygous variants in SPATA7 that were predicted to be pathogenic.

CONCLUSIONS

Compound heterozygous c.1100A > G, p.(Y367C) and c.1102_1103delCT, p.(L368Efs*4) variants in SPATA7 manifest as an unusual RP phenotype in this case, showing extensive choroidal sclerosis and retinal pigment epithelium (RPE) atrophy with evidence of progression over two years on multimodal imaging.

Correction of Monogenic and Common Retinal Disorders with Gene Therapy

The past decade has seen major advances in gene-based therapies, many of which show promise for translation to human disease. At the forefront of research in this field is ocular disease, as the eye lends itself to gene-based interventions due to its accessibility, relatively immune-privileged status, and ability to be non-invasively monitored. A landmark study in 2001 demonstrating successful gene therapy in a large-animal model for Leber congenital amaurosis set the stage for translation of these strategies from the bench to the bedside. Multiple clinical trials have since initiated for various retinal diseases, and further improvements in gene therapy techniques have engendered optimism for alleviating inherited blinding disorders. This article provides an overview of gene-based strategies for retinal disease, current clinical trials that engage these strategies, and the latest techniques in genome engineering, which could serve as the next frontline of therapeutic interventions.