This study evaluated the safety and tolerability of ocular RS1 adeno-associated virus (AAV8-RS1) gene augmentation therapy to the retina of participants with X-linked retinoschisis (XLRS). XLRS is a monogenic trait affecting only males, caused by mutations in the RS1 gene. Retinoschisin protein is secreted principally in the outer retina, and its absence results in retinal cavities, synaptic dysfunction, reduced visual acuity, and susceptibility to retinal detachment. This phase I/IIa single-center, prospective, open-label, three-dose-escalation clinical trial administered vector to nine participants with pathogenic RS1 mutations. The eye of each participant with worse acuity (≤63 letters; Snellen 20/63) received the AAV8-RS1 gene vector by intravitreal injection. Three participants were assigned to each of three dosage groups: 1e9 vector genomes (vg)/eye, 1e10 vg/eye, and 1e11 vg/eye. The investigational product was generally well tolerated in all but one individual. Ocular events included dose-related inflammation that resolved with topical and oral corticosteroids. Systemic antibodies against AAV8 increased in a dose-related fashion, but no antibodies against RS1 were observed. Retinal cavities closed transiently in one participant. Additional doses and immunosuppressive regimens are being explored to pursue evidence of safety and efficacy (ClinicalTrials.gov: NCT02317887).

Gene therapy for inherited retinal diseases has been shown to ameliorate functional and structural defects in both animal models and in human clinical trials. X-linked retinoschisis (XLRS) is an early-age onset macular dystrophy resulting from loss of an extracellular matrix protein (RS1). In preparation for a human clinical gene therapy trial, we conducted a dose-range efficacy study of the clinical vector, a self-complementary AAV vector delivering a human retinoschisin (RS1) gene under control of the RS1 promoter and an interphotoreceptor binding protein enhancer (AAV8-scRS/IRBPhRS), in the retinoschisin knockout (Rs1-KO) mouse. The therapeutic vector at 1x106 – 2.5x109 (1E6-2.5E9) vector genomes (vg)/eye or vehicle was administered to one eye of 229 male Rs1-KO mice by intravitreal injection at 22 ± 3 days postnatal age (PN). Analysis of retinal function (dark-adapted electroretinogram, ERG), structure (cavities and outer nuclear layer thickness) by in vivo retinal imaging using optical coherence tomography (OCT), and retinal immunohistochemistry (IHC) for RS1 was done 3 to 4 months and/or 6 to 9 months post-injection (PI). RS1 IHC staining was dose-dependent across doses ≥ 1E7 vg/eye, and the threshold for significant improvement in all measures of retinal structure and function was 1E8 vg/eye. Higher doses, however, did not produce additional improvement. At all doses showing efficacy, RS1 staining in Rs1-KO mouse was less than in wild type (WT) mice. Improvement in the ERG and RS1 staining was unchanged or greater at 6 to 9 months than at 3 to 4 months PI. This study demonstrates that vitreal administration of AAV8 scRS/IRBPhRS produces significant improvement in retinal structure and function in the mouse model of XLRS over a vector dose range that can be extended to a human trial. It indicates that fully normal RS1 expression is not necessary for a therapeutic effect.

Purpose: To investigate the retinal structure and function during the progression of X-linked retinoschisis (XLRS) from childhood to adulthood. Methods: Ten patients clinically diagnosed with XLRS were investigated at 6–15 years of age (mean age 9 years) with a follow-up 8 to 14 years later (mean 12 years). The patients underwent regular ophthalmic examination as well as testing of best corrected visual acuity (BCVA), visual field (VF) and assessment of full-field electroretinography (ERG) during their first visit. During the follow-up, the same clinical protocols were repeated. In addition, macular structure and function was examined with multifocal electroretinography (mfERG) and optical coherence tomography (OCT). The patients were 18–25 years of age (mean age 21 years) at the follow-up examination. All exons and exon-intron boundaries of RS1-gene were sequenced for gene mutations in 9 out of the 10 patients. Results: Best corrected VA and VF were stable during this follow-up period. No significant progression in cone or rod function could be measured by full-field ERG. Multifocal electroretinography and OCT demonstrated a wide heterogeneity of macular changes in retinal structure and function at the time of follow-up visit. Three different mutations were detected in these nine patients, including a known nonsense mutation in exon 3, a novel insertion in exon 5 and an intronic mutation at 5′ splice site of intron 3. Conclusions: Clinical follow-up (mean 12 years) of ten young XLRS patients (mean age of 9 years) with a typical congenital retinoschisis phenotype revealed no significant decline in retinal function during this time period. MfERG and OCT demonstrated a wide variety of macular changes including structure and dysfunction. The XLRS disease was relatively stable during this period of observation and would afford opportunity for therapy studies to judge benefit against baseline and against the fellow eye.

In the present era of evolving gene-based therapies for inherited retinal dystrophies (IRDs), it has become increasingly important to verify the genotype in every case, to identify all subjects eligible for treatment. Moreover, combined insight concerning phenotypes and genotypes is crucial for improved understanding of thevisual impairment, prognosis, and inheritance. The objective of this study was to investigate to what extent renewed comprehensive genetic testing of patients diagnosed with IRD but with previously inconclusive DNA test results can verify the genotype, if confirmation of the genotype has an impact on the understanding of the clinical picture, and, to describe the genetic spectrum encountered in a Swedish IRD cohort. The study included 279 patients from the retinitis pigmentosa research registry (comprising diagnosis within the whole IRD spectrum), hosted at the Department of Ophthalmology, Skåne University hospital, Sweden. The phenotypes had already been evaluated with electrophysiology and other clinical tests, e.g., visual acuity, Goldmann perimetry, and fundus imaging at the first visit, sometime between 1988–2015 and the previous—in many cases, multiple—genetic testing, performed between 1995 and 2020 had been inconclusive. All patients were aged 0–25 years at the time of their first visit. Renewed genetic testing was performed using a next generation sequencing (NGS) IRD panel including 322 genes (Blueprint Genetics). Class 5 and 4 variants, according to ACMG guidelines, were considered pathogenic. Of the 279 samples tested, a confirmed genotype was determined in 182 (65%). The cohort was genetically heterogenous, including 65 different genes. The most prevailing were ABCA4 (16.5%), RPGR (6%), CEP290 (6%), and RS1 (5.5%). Other prevalent genes were CACNA1F (3%), PROM1 (3%), CHM (3%), and NYX (3%). In 7% of the patients there was a discrepancy between the diagnosis made based on phenotypical or genotypical findings alone. To conclude, repeated DNA-analysis was beneficial also in previously tested patients and improved our ability to verify the genotype–phenotype association increasing the understanding of how visual impairment manifests, prognosis, and the inheritance pattern. Moreover, repeated testing using a widely available method could identify additional patients eligible for future gene-based therapies.