Differences in Intraretinal Pigment Migration Across Inherited Retinal Dystrophies

Cross-Sectional Analysis of Outer Retinal Tubulation in Inherited Retinal Diseases: A Multicenter Study

PURPOSE

This study aims to explore genetic variants that potentially lead to outer retinal tubulation (ORT), estimate the prevalence of ORT in these candidate genes, and investigate the clinical etiology of ORT in patients with inherited retinal diseases (IRDs), with respect to each gene.

DESIGN

Retrospective cohort study.

METHODS

A retrospective cross-sectional review was conducted on 565 patients with molecular diagnoses of IRD, confirming the presence of ORT as noted in each patient's respective spectral-domain optical coherence tomography (SD-OCT) imaging. Using SD-OCT imaging, the presence of ORT was analyzed in relation to specific genetic variants and phenotypic characteristics. Outcomes included the observed ORT frequencies across 2 gene-specific cohorts: non-retinal pigment epithelium (RPE)-specific genes, and RPE-specific genes; and to investigate the analogous characteristics caused by variants in these genes.

RESULTS

Among the 565 patients included in this study, 104 exhibited ORT on SD-OCT. We observed ORT frequencies among the following genes from our patient cohort: 100% (23/23) for CHM, 100% (2/2) for PNPLA6, 100% (4/4) for RCBTB1, 100% for mtDNA [100% (4/4) for MT-TL1 and 100% (1/1) for mtDNA deletion], 100% (1/1) for OAT, 95.2% (20/21) for CYP4V2, 72.7% (8/11) for CHM female carriers, 66.7% (2/3) for C1QTNF5, 57.1% (8/14) for PROM1, 53.8% (7/13) for PRPH2, 42.9% (3/7) for CERKL, 28.6% (2/7) for CDHR1, 20% (1/5) for RPE65, 4% (18/445) for ABCA4. In contrast, ORT was not observed in any patients with photoreceptor-specific gene variants, such as RHO (n = 13), USH2A (n = 118), EYS (n = 70), PDE6B (n = 10), PDE6A (n = 4), and others.

CONCLUSIONS

These results illustrate a compelling association between the presence of ORT and IRDs caused by variants in RPE-specific genes, as well as non-RPE-specific genes. In contrast, IRDs caused by photoreceptor-specific genes are typically not associated with ORT occurrence. Further analysis revealed that ORT tends to manifest in IRDs with milder intraretinal pigment migration (IPM), a finding that is typically associated with RPE-specific genes. These findings regarding ORT, genetic factors, atrophic patterns in the fundus, and IPM provide valuable insight into the complex etiology of IRDs. Future prospective studies are needed to further explore the association and underlying mechanisms of ORT in these contexts.

RBP3-Retinopathy-Inherited High Myopia and Retinal Dystrophy: Genetic Characterization, Natural History, and Deep Phenotyping

PURPOSE

To examine the genetic and clinical features and the natural history of RBP3-associated retinopathy.

DESIGN

Multi-center international, retrospective, case series of adults and children, with moleculraly confirmed RBP3-asociated retinopathy.

METHODS

The genetic, clinical, and retinal imaging findings, including optical coherence tomography (OCT) and fundus autofluorescence (FAF), were investigated both cross-sectionally and longitudinally. The results of international standard full-field electroretinography (ERG) and pattern electroretinography (PERG) were reviewed.

RESULTS

We ascertained 12 patients (5 female and 7 male) from 10 families (4 patients previously reported). Ten novel disease-causing RBP3 variants were identified. Ten patients were homozygous. The mean age (±SD, range) of the group was 21.4 years (±19.1, 2.9-60.5 years) at baseline evaluation. All 12 patients were highly myopic, with a mean spherical equivalent of -16.0D (range, -7.0D to -33.0D). Visual acuity was not significantly different between eyes, and no significant anisometropia was observed. Mean best-corrected visual acuity (BCVA) was 0.48 logMAR (SD, ±0.29; range, 0.2-1.35 logMAR); at baseline. Eleven patients had longitudinal BCVA assessment, with a mean BCVA of 0.46 logMAR after a mean follow-up of 12.6 years. All patients were symptomatic with reduced VA and myopia by the age of 7 years old. All patients had myopic fundi and features in keeping with high myopia on OCT, including choroidal thinning. The 4 youngest patients had no fundus pigmentary changes, with the rest of the patients presenting with a variable degree of mid-peripheral pigmentation and macular changes. FAF showed variable phenotypes, ranging from areas of increased signal to advanced atrophy in older patients. OCT showed cystoid macular edema at presentation in 3 patients, which persisted during follow-up in 2 patients and resolved to atrophy in the third patient. The ERGs were abnormal in 9 of 9 cases, revealing variable relative involvement of rod and cone photoreceptors with additional milder dysfunction post-phototransduction in some. All but 1 patient had PERG evidence of macular dysfunction, which was severe in most cases.

CONCLUSIONS

This study details the clinical and functional phenotype of RBP3-retinopathy in the largest cohort reported to date. RBP3-retinopathy is a disease characterized by early onset, slow progression over decades, and high myopia. The phenotypic spectrum and natural history as described herein has prognostic and counseling implications. RBP3-related disease should be considered in children with high myopia and retinal dystrophy.

RETINITIS PIGMENTOSA SINE PIGMENTO: Clinical Spectrum and Pigment Development

PURPOSE

To investigate the clinical findings, natural course, and pigment development of patients with retinitis pigmentosa (RP) sine pigmento using multimodal imaging.

METHODS

We reviewed the medical records of 810 consecutive patients with RP and assessed serial ultra-widefield fundus photography, fundus autofluorescence, and optical coherence tomography images. Electrophysiological and visual field analysis findings were also reviewed.

RESULTS

Of the 774 patients with RP who met the inclusion criteria, 88 were diagnosed with RP sine pigmento, with a prevalence of 11.4%. The mean age of the patients was 35.57 years compared with 49.83 years for patients with typical RP. Fifty-nine patients (67%) demonstrated minimal color change, whereas 29 (33%) presented with grayish flecks in the retinal pigment epithelium on fundus photography. All patients with RP sine pigmento had abnormalities on fundus autofluorescence, and the commonest fundus autofluorescence findings were punctate or reticular hypoautofluorescence. Of the 62 patients without pigmentation at the first visit and at the follow-up visits, 14 (22.6%) had developed pigmentation at their follow-up visit, with an average time of 3.92 years. Most patients retained a visual acuity of ≥20/50 within the age of 50 years.

CONCLUSION

Diagnosing RP sine pigmento based solely on ophthalmoscopic findings is more difficult than in more typical cases. Multimodal imaging can provide insights into the clinical characteristics to facilitate the diagnosis, classification, and follow-up of patients.

Retinal Manifestations of Mitochondrial Oxidative Phosphorylation Disorders

Purpose

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

Methods

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

Results

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

Conclusions

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

Association of a Novel Intronic Variant in RPGR With Hypomorphic Phenotype of X-Linked Retinitis Pigmentosa

Importance

Pathogenic variants in retinitis pigmentosa GTPase regulator (RPGR) gene typically lead to a severe form of X-linked retinitis pigmentosa, which is associated with early severe vision loss.

Objective

To investigate an X-linked retinal degeneration family with atypical preservation of visual acuity in the presence of a novel deep intronic splice site RPGR c.779-5T>G variant.

Design, Setting, and Participants

In this case series, 3 members of an X-linked retinal degeneration family were studied by in-depth phenotyping and genetic screening at a single center. Data were collected and analyzed from November 2018 to March 2020.

Main Outcomes and Measures

Data were collected on full ophthalmic history, examination, and retinal imaging. A full retinitis pigmentosa gene panel was analyzed by next-generation sequencing. The pathogenicity of the RPGR c.779-5T>G variant was assessed by in silico splice prediction tools and by purpose-designed in vitro splicing assay.

Results

An 84-year-old man was referred with clinical diagnosis of choroideremia and possible inclusion into a gene therapy trial. He presented with late-stage retinal degeneration and unusually preserved visual acuity (78 and 68 ETRDS letters) that clinically resembled choroideremia. His 23-year-old grandson was still in early stages of degeneration but showed a very different clinical picture, typical of retinitis pigmentosa. Next-generation sequencing identified a sole RPGR c.779-5T>G variant of undetermined pathogenicity in both cases. The daughter of the proband showed an RPGR carrier phenotype and was confirmed to carry the same variant. The molecular analysis confirmed that the RPGR c.779-5T>G variation reduced the efficiency of intron splicing compared with wild type, leading to a population of mutant and normal transcripts. The predicted consequences of the pathogenic variant are potential use of an alternative splice acceptor site or complete skipping of exon 8, resulting in truncated forms of the RPGR protein with different levels of glutamylation.

Conclusions and Relevance

These results support the importance of careful interpretation of inconsistent clinical phenotypes between family members. Using a molecular splicing assay, a new pathogenic variant in a noncoding region of RPGR was associated with a proportion of normal and hypomorphic RPGR, where cones are likely to survive longer than expected, potentially accounting for the preserved visual acuity observed in this family.