Intereye Symmetry in Bietti Crystalline Dystrophy

Longitudinal structure-function analysis of molecularly-confirmed CYP4V2 Bietti Crystalline Dystrophy

OBJECTIVES

Bietti Crystalline Dystrophy (BCD) is an autosomal recessive progressive retinal disease caused by mutations in CYP4V2. We have characterised the natural history including structural and functional measures to identify potential outcome metrics for future clinical trials.

METHODS

Molecularly-confirmed BCD patients with biallelic variants in CYP4V2 were retrospectively identified from Moorfields Eye Hospital (UK). Clinical details including results of molecular genetic testing, best-corrected visual acuity (BCVA) and spectral-domain optical coherence tomography (OCT) scans were extracted. From OCT scans, ellipsoid zone (EZ) measures, foveal thickness of the whole retina, outer retina and choroid were measured. Age-related changes of clinical parameters were assessed with linear mixed models.

RESULTS

Twenty-eight BCD patients were identified, with median age at baseline of 37 years (interquartile range [IQR]: 30-49.5). Median follow-up was 7.7 years (IQR: 3.4-14.5). Most patients (41.7%) showed chorioretinal atrophy at baseline. All OCT parameters showed significant age-related loss (p < 0.05), with EZ measures and choroidal thickness displaying the most rapid degeneration (2.3-3.3% per year vs 0.6-1.5% per year). Median BCVA was 0.2 LogMAR (IQR: 0-0.5) at baseline and showed small age-related loss ( + 0.016 LogMAR per year, p = 0.0019). Patients exhibited substantial phenotypic variability.

CONCLUSIONS

BCD presents between age 25 and 40, and slowly progresses to an advanced chorioretinal atrophy and vision loss by age 60. BCVA may be preserved until late, and is seemingly poorly representative of disease progression. OCT parameters capturing EZ and choroid changes may afford more suitable trial outcome measures.

Longitudinal Natural History Study of Visual Function in Bietti Crystalline Dystrophy: Implications for Early Intervention

Purpose

To delineate the natural history of visual function parameters over time in individuals with Bietti crystalline dystrophy.

Methods

This was a single-center retrospective longitudinal cohort study. Participants (n = 29) with a clinical diagnosis of Bietti crystalline dystrophy who harbored two alleles of disease-causing variants of the cytochrome P450 family 4 subfamily V member 2 gene (CYP4V2) were enrolled. Best-corrected visual acuity (BCVA), visual field (VF), and full-field ERG (ffERG) at baseline and their changes during the follow-up period were evaluated. Annual progression rates were calculated using three methods.

Results

The mean age at the initial visit was 34.2 ± 7.5 years, with 5.9 ± 3.1 years follow-up. The annual progression rate from the longitudinal analysis using averaged individual progression rates was 0.079 logMAR units for BCVA, 1.14 dB for mean defect (MD) value of VF, and -18.06 µV and -5.45 µV for the b-wave amplitudes of scotopic 3.0 ERG and photopic 3.0 ERG, respectively. Mixed-model linear regression revealed annual progression rates of 0.068 logMAR units, 0.86 dB, -13.29 µV, and -3.75 µV, respectively. Cross-sectional progression rates from visual function versus age at baseline were 0.011 logMAR units, 0.47 dB, -1.85 µV, and -1.07 µV, respectively, which were significantly slower than those from the longitudinal data. Interocular symmetries for the MD values of VF and ffERG were good.

Conclusions

Annual BCVA, VF, and ffERG progression rates were rapid, emphasizing the need for regular follow-up and early intervention. The progression rate cannot be inferred accurately from cross-sectional data from patients of different ages.

Morphological and functional parameters in X-linked retinoschisis patients-A multicentre retrospective cohort study

Introduction

X-linked retinoschisis (XLRS) is a potential target for gene supplementation approaches. To establish potential structural and functional endpoints for clinical trials, a comprehensive understanding of the inter-eye symmetry, relationship between structural and functional parameters, and disease progression is vital.

Methods

In this retrospective multicentre study, 118 eyes of 59 XLRS patients with RS1 mutations were assessed. Information from center databases included: RS1 variant; age at presentation; best-corrected visual acuity (BCVA), central retinal thickness (CRT), macular volume (MV) at presentation and at the last follow up; full-field electroretinogram (ERG) findings; presence of peripheral retinoschisis and complications (vitreous hemorrhage, retinal detachment); treatment with systemic or topical carbonic anhydrase inhibitors (CAI).

Results

Inter-eye symmetry revealed strong correlation in CRT (r = 0.77; p < 0.0001) and moderate correlations in MV (r = 0.51, p < 0.0001) and BCVA (r = 0.49; p < 0.0001). Weak or no correlations were observed between BCVA and structural parameters (CRT, MV). Peripheral retinoschisis was observed in 40 (68%), retinal detachment in 9 (15%), and vitreous hemorrhage in 5 (8%) patients, respectively. Longitudinal examinations (mean, 4.3 years) showed no BCVA changes; however, a reduction of the CRT (p = 0.02), and MV (p = 0.01) was observed. Oral and/or topical CAI treatment did not significantly alter the CRT (p = 0.34).

Discussion

The XLRS phenotype demonstrates a strong CRT symmetry between the eyes within individual patients and stable BCVA over several years. BCVA exhibits a weak correlation with the morphological parameters of retinal thickness (CRT MV). In our cohort, longitudinal functional changes were not significant, likely attributed to the short average follow-up period. Furthermore, CAI treatment didn't influence both morphological and functional outcomes.

Bietti's crystalline dystrophy: genotyping and deep qualitative and quantitative phenotyping in preparation for clinical trials

PURPOSE

To qualitatively and quantitatively characterise the genotypes and phenotypes of Bietti's crystalline dystrophy (BCD) in a cohort of patients.

DESIGN

Cross-sectional and observational study.

METHODS

Clinically confirmed BCD patients were recruited for genotyping and phenotyping. Multiple retinal imaging modalities were employed. Atrophy in the fovea was adopted as major consideration for staging strategy, while percentage area of autofluorescence (AF) atrophy (PAFA) in the macula was determined for quantitation.

RESULTS

In 74 clinically diagnosed BCD patients, c.802-8_810del17insGC was shown the predominant variant of the CYP4V2 gene (allele frequency 55.4%). Sixty-two cases (123 eyes) with full imaging data were classified according to a modified criterion into stages 1 (n=8, 6.50%), 2A (n=9, 7.32%), 2B (n=17, 13.82%), 3A (n=30, 24.39%) and 3B (n=59, 47.97%). The eyes of the stage 2B were particularly deemed 'high risk' due to atrophy near fovea, while in stage 3A, though with remarkable foveal atrophy, preserved retinal pigment epithelium/photoreceptor islands near the fovea were found in 14 eyes. A tendency of increase in PAFA with age was found (rs=0.31, p=0.014). Significant PAFA increase was shown through stages 1 to 3B, and best-corrected visual acuity (BCVA, Logarithm of the Minimum Angle of Resolution) was shown to moderately correlate with PAFA (rs=0.56, p<0.001).

CONCLUSION

The PAFA might be an efficient biomarker for BCD severities correlating with BCVA. The highly heterogeneous chorioretinopathy and BCVA of BCD cases appear to be associated with disease stages, progression types and patients' ages. Foveal involvement should be of a major concern for consideration of potential therapeutic intervention.

Diagnostic and Management Strategies of Bietti Crystalline Dystrophy: Current Perspectives

Bietti crystalline dystrophy (BCD) is a rare, genetically determined chorioretinal dystrophy presenting with intraretinal crystalline deposits and varying degrees of progressive chorioretinal atrophy commencing at the posterior pole. In some cases, there can be concomitant corneal crystals noted first in the superior or inferior limbus. CYP4V2 gene, a member of the cytochrome P450 family is responsible for the disease and more than 100 mutations have been defined thus far. However, a genotype-phenotype correlation has not been established yet. Visual impairment commonly occurs between the second and third decades of life. By the fifth or sixth decade of life, vision loss can become so severe that the patient may potentially become legally blind. Multitudes of multimodal imaging modalities can be utilized to demonstrate the clinical features, course, and complications of the disease. This present review aims to reiterate the clinical features of BCD, update the clinical perspectives with the help of multimodal imaging techniques, and overview its genetic background with future therapeutic approaches.

Foveolar thickness as potential standardized structural outcome measurement in studies of Bietti crystalline dystrophy

Bietti crystalline dystrophy (BCD) is an ultra-rare orphan disorder that can lead to blindness. Because of the variable rates of progression of the disease, it is necessary to identify suitable outcome measurements for tracking progression in BCD. A retrospective analysis of patients with a clinical and genetic diagnosis of BCD was conducted. Four measurements of spectral domain-optical coherence tomography were compared to patients’ best corrected visual acuity. We observed that patients with higher measurements of foveolar thickness, choroidal thickness in the foveolar region, ellipsoid zone band length and the outer nuclear layer + area, had on average better visual acuity. Future studies are needed to validate the structural–functional correlations we observed in BCD and to propose a sensitive and clinically meaningful outcome measurement for tracking this rare, variable disease.

Victorian evolution of inherited retinal diseases natural history registry (VENTURE study): Rationale, methodology and initial participant characteristics

BACKGROUND

Emerging treatments are being developed for inherited retinal diseases, requiring a clear understanding of natural progression and a database of potential participants for clinical trials. This article describes the rationale, study design and methodology of the Victorian Evolution of inherited retinal diseases NaTUral history REgistry (VENTURE), including data from the first 150 participants enrolled.

METHODS

VENTURE collects retrospective and prospective data from people with inherited retinal diseases. Following registration, participants are asked to attend a baseline examination using a standardised protocol to confirm their inherited retinal disease diagnosis. Examination procedures include (i) retinal function, using visual acuity and perimetry; (ii) retinal structure, using multimodal imaging and (iii) patient-reported outcomes. Participants' molecular diagnoses are obtained from their clinical records or through targeted-panel genetic testing by an independent laboratory. Phenotype and genotype data are used to enrol participants into disease-specific longitudinal cohort sub-studies.

RESULTS

From 7 July 2020 to 30 December 2021, VENTURE enrolled 150 registrants (138 families) and most (63%) have a rod-cone dystrophy phenotype. From 93 participants who have received a probable molecular diagnosis, the most common affected genes are RPGR (13% of all registrants), USH2A (10%), CYP4V2 (7%), ABCA4 (5%), and CHM (5%). Most participants have early to moderate vision impairment, with over half (55%) having visual acuities of better than 6/60 (20/200) at registration.

CONCLUSIONS

The VENTURE study will complement existing patient registries and help drive inherited retinal disease research in Australia, facilitating access to research opportunities for individuals with inherited retinal diseases.