Mutations in Receptor Expression Enhancing Protein 6 (REEP6) Cause Early Onset RP in Humans.

Abstract

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 disease-causing 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.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.