RBP3-retinopathy - inherited high myopia and retinal dystrophy: Genetic Characterization, Natural History, and Deep Phenotyping

Objective: To examine the genetic and clinical features and the natural history of RBP3-associated retinopathy. // Design: Multi-center international, retrospective, case series. // Setting: Three tertiary referral centers. // Participants: Adults and children, with molecularly confirmed RBP3-associated retinopathy. // Main Outcomes and Measures: Multi-center, international, retrospective, consecutive observational study in three tertiary referral centers of adults and children, with molecularly confirmed RBP3-retinopathy. 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 and pattern electroretinography (ERG; PERG) were reviewed. // Results: We ascertained 12 patients (5 females), from 10 families, with four patients previously reported. Eight 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 (range; 0.2-1.35, SD; ± 0.29 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. 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 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 three patients, which persisted during follow-up in two patients and resolved to atrophy for 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 one had PERG evidence of macular dysfunction, severe in most. // 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 counselling implications. RBP3-related disease should be considered in children with high myopia and retinal dystrophy

Clinical and Therapeutic Evaluation of the Ten Most Prevalent <i>CRB1</i> Mutations

Mutations in the Crumbs homolog 1 (CRB1) gene lead to severe inherited retinal dystrophies (IRDs), accounting for nearly 80,000 cases worldwide. To date, there is no therapeutic option for patients suffering from CRB1-IRDs. Therefore, it is of great interest to evaluate gene editing strategies capable of correcting CRB1 mutations. A retrospective chart review was conducted on ten patients demonstrating one or two of the top ten most prevalent CRB1 mutations and receiving care at Columbia University Irving Medical Center, New York, NY, USA. Patient phenotypes were consistent with previously published data for individual CRB1 mutations. To identify the optimal gene editing strategy for these ten mutations, base and prime editing designs were evaluated. For base editing, we adopted the use of a near-PAMless Cas9 (SpRY Cas9), whereas for prime editing, we evaluated the canonical NGG and NGA prime editors. We demonstrate that for the correction of c.2843G>A, p.(Cys948Tyr), the most prevalent CRB1 mutation, base editing has the potential to generate harmful bystanders. Prime editing, however, avoids these bystanders, highlighting its future potential to halt CRB1-mediated disease progression. Additional studies investigating prime editing for CRB1-IRDs are needed, as well as a thorough analysis of prime editing’s application, efficiency, and safety in the retina