Novel RS1 Mutation in an Irish X-Linked Retinoschisis Cohort

Program Number: 6585 Poster Board Number: D0356 Presentation Time: 11:00 AM–12:45 PM Novel RS1 Mutation in an Irish X-Linked Retinoschisis Cohort Kirk Stephenson1, Matthew Carrigan2, Paul Kenna3, 2, G Jane Farrar2, David Keegan1. 1Ophthalmology, Mater Misericordiae University Hospital, Dublin, Ireland; 2Trinity College Dublin, Dublin, Ireland; 3Ophthalmology, Royal Victoria Eye & Ear Hospital, Dublin, Ireland. Purpose: To describe the phenotype and genotype of a family cohort (observational study, n=6) of X-linked retinoschisis in an Irish population with a novel RS1 mutation. Methods: Patients were recruited as part of the Irish national genetic screening registry for inherited retinal degenerations. This screening program includes clinical history and examination with retinal imaging, electrophysiology, visual field testing and genetic analysis. Six patients (age 62y – 74y) were identified with X-linked retinoschisis (five brothers, one male first cousin). Next generation sequencing (NGS) was performed for each patient. Investigation into the family history revealed 5 grandsons and a further maternal male first cousin that are affected. Results: All had a history of visual acuity and colour vision disturbance from childhood. There was significant phenotypic variability between the six subjects. The youngest and least severely affected patient had one eye enucleated; the remaining eye had a normal macular appearance, with vitreous strands. The eldest and most severely affected patient had advanced macular atrophy. The four patients of intermediate age and severity had a more classic macular retinoschisis pattern of retinal splitting. NGS detected a novel RS1 gene mutation (X chromosome); this was a single base change (c.413C>A) in exon 5. This mutation had not been previously submitted to the Retinoschisis Consortium, but a different mutation at this codon (c.412A>G) has been describe, which leads to a deficiency of the retinoschisin protein. Conclusions: This family has a novel gene mutation in the RS1 gene with clinical retinoschisis. The next step is to investigate the male children of these patients’ daughters for retinoschisis and this RS1 mutation. We aim to collaborate with current research in the development of gene therapy for treatment of RS1 gene mutations. Those with more advanced macular atrophy will have limited potential for improvement; however, the primary beneficiaries of gene therapy are the younger generation. With early clinical and genetic detection of X-linked retinoschisis phenotype/genotype in genetically predisposed individuals, permanent central visual loss may be prevented. Commercial Relationships: Kirk Stephenson, None; Matthew Carrigan, None; Paul Kenna, None; G Jane Farrar, None; David Keegan, None Program Number: 6586 Poster Board Number: D0357 Presentation Time: 11:00 AM–12:45 PM Mutations in Receptor Expression Enhancing Protein 6 (REEP6) Cause Early Onset RP in Humans Smriti Agrawal1, 2, Aiden Eblimit1, 2, Feng Wang1, 2, Mingchu Xu1, 2, Kerry Goetz3, Yumei Li1, 2, Rui Chen1, 2. 1Molecular and Human Genetics, Baylor College of Medicine, Houston, TX; 2Human Genome Sequencing Center, Baylor College of Medicine, Houston, TX; 3Ophthalmic Genetics and Visual Function Branch, National Eye Institute/National Institutes of Health, Bethesda, MD. Purpose: Retinitis pigmentosa is a genetically heterogeneous disorder characterized by rod photoreceptor degeneration and is a leading cause of blindness worldwide. Currently, the genetic basis of about 40% of autosomal recessive (arRP) patients remains unknown. Here we report the identification and characterization of REEP6 (Receptor Expression Enhancing Protein 6) as a novel diseasecausing gene associated with arRP. Methods: Whole exome sequencing (WES) was performed on a cohort of unassigned RP patients previously screened with retinal capture sequencing for mutations in known disease-genes. To test the pathogenicity of the mutation identified in the patient, we used CRISPR/Cas9 mediated targeting to generate knock-in mice carrying the patient mutation. Immunohistochemistry was performed to examine expression and localization of the protein in the retina. To study retinal function, we performed scotopic and photopic retinal electroretinography (ERG). Optical Coherence Tomography (OCT), histological analysis, and immunohistochemistry were performed to further characterize morphological defects. Results: WES data analysis led to the identification of bi-allelic mutations in REEP6 in a patient with early-onset arRP. To confirm the pathogenicity of the patient mutation, we generated corresponding CRISPR-targeted knock-in mice. Immunostaining of WT retina confirmed the previously reported expression of Reep6 specifically in the outer segment (OS) of the rod photoreceptors, the outer nuclear layer (ONL), and the outer plexiform layer (OPL). Consistent with the phenotypes observed in the patient, Reep6 mutant mice exhibit progressive retinal degeneration with abnormal scotopic ERG response starting at 3 months of age, indicative of progressive rod dysfunction. OCT and histological analysis of Reep6 mutant mice show significant thinning of the ONL and photoreceptor degeneration. Conclusions: This study is the first to identify mutations in REEP6 that cause retinitis pigmentosa in humans. Furthermore, we have developed Reep6 knock-in mice that model the human disease, enabling us to gain insights into Reep6 dysfunction in photoreceptor degeneration. Our results suggest that Reep6 plays an important role in preserving proper photoreceptor function and survival. Commercial Relationships: Smriti Agrawal, None; Aiden Eblimit, None; Feng Wang, None; Mingchu Xu, None; Kerry Goetz; Yumei Li, None; Rui Chen, None Support: NEI Grant R01EY022356 and R01EY018571, Foundation Fighting Blindness Grant BR-GE-0613-0618-BCM