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

Journal article

IntroductionX-linked retinoschisis (XLRS) is a vitreoretinal dystrophy caused by RS1 gene mutations which disrupt retinoschisin-1 (RS1) function. Vital for retinal architecture, the absence of functional RS1 leads to the development of intraretinal cysts. Intravitreal injection of a gene therapy for treating XLRS caused ocular inflammation in high dose groups in a phase I/II clinical trial. This study investigates a low dose subretinal gene therapy in Rs1 knockout (Rs1-KO) mice compared to injection of buffer alone. Observation of an unexpected therapeutic effect following the subretinal injection of the hypertonic buffer led to novel findings in XLRS.MethodsRs1-KO mice were subretinally injected with an AAV2/4 vector (n = 10) containing the RS1 gene driven by an Ef1α promoter, a hypertonic buffer (n = 15) (180 mM NaCl 0.001% F68/PBS (pH 7.4)), or isotonic buffer (n = 7) (155.2 mM NaCl 0.001% F68/PBS, pH 7.0). A sham puncture group was also included (n = 6). Endpoints included electroretinogram (ERG), optical coherence tomography (OCT), a visually guided swim assay (VGSA), and immunohistochemistry.ResultsUnexpectedly, hypertonic buffer-injected eyes had reduced cyst severity at 1-month post-injection (MPI) (p < 0.0001), higher amplitudes in cone-dominant ERGs persisting to 5 MPI (5 Hz flicker; p < 0.0001; 3.0 flash; p = 0.0033) and a trend for improved navigational vision in the light compared to untreated Rs1-KO eyes. To investigate the role of tonicity on this effect, an isotonic buffer-injected cohort was created (155.2 mM NaCl 0.001% F68/PBS, pH 7.0) (n = 7). Surprisingly, hypertonic buffer-injected eyes exhibited a greater reduction in cyst severity and demonstrated improved cone-dominant ERG metrics over isotonic buffer-injected and sham puncture eyes. An immunohistochemistry assay demonstrated greater cone density in hypertonic buffer-injected eyes than untreated Rs1-KO eyes at 5–6 MPI (p = 0.0198), suggesting a possible cone preservation mechanism. Moreover, our findings reveal a negative correlation between the peak severity of cysts and long-term ERG amplitudes in cone-dominant pathways, implying that effectively managing cysts could yield enduring benefits for cone function.Discussion/conclusionThis study presents evidence that cyst resolution can be triggered through an osmolarity-dependent pathway, and early cyst resolution has long-term effects on cone signaling and survival, offering potential insights for the development of novel treatments for XLRS patients

Authors: Kiraly, P; Seitz, IP; Elsayed, MEAA; Downes, SM; Patel, CK

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Frontiers Media
• Journal: Frontiers in Medicine
• Volume: 10
• Pages: 1331889-1331889
• Article number: 1331889
• Publication date: 2024-01-11
• DOI: 10.3389/fmed.2023.1331889
• EISSN: 2296-858X
• ISSN: 2296-858X
• Language: English
• Keywords: Medicine; Retinoschisis; Retinal; Electroretinography; Ophthalmology; Visual acuity; Erg; Retinal detachment; Internal medicine; Retrospective cohort study; Cohort