Retinal Structure and Function in a Knock-in Mouse Model for the FAM161A-p.Arg523∗ Human Nonsense Pathogenic Variant

Purpose: Pathogenic variants in FAM161A are the most common cause of retinitis pigmentosa in Israel. Two founder pathogenic variants explain the vast majority of cases of Jewish origin, 1 being a nonsense variant (p.Arg523∗). The aim of this study was to generate a knock-in (KI) mouse model harboring the corresponding p.Arg512∗ pathogenic variant and characterize the course of retinal disease. Design: Experimental study of a mouse animal model. Subjects/Participants/Controls: A total of 106 Fam161a knock-in mice and 29 wild-type mice with C57BL/6J background particiapted in this study. Methods: Homozygous Fam161a p.Arg512∗ KI mice were generated by Cyagen Biosciences. Visual acuity (VA) was evaluated using optomotor tracking response and retinal function was assessed by electroretinography (ERG). Retinal structure was examined in vivo using OCT and fundus autofluorescence imaging. Retinal morphometry was evaluated by histologic and immunohistochemical (IHC) analyses. Main Outcome Measures: Visual and retinal function assessments, clinical imaging examinations, quantitative histology, and IHC studies of KI as compared with wild-type (WT) mice retinas. Results: The KI model was generated by replacing 3 bp, resulting in p.Arg512∗. Homozygous KI mice that had progressive loss of VA and ERG responses until the age of 18 months, with no detectable response at 21 months. OCT showed complete loss of the outer nuclear layer at 21 months. Fundus autofluorescence imaging revealed progressive narrowing of blood vessels and formation of patchy hyper-autofluorescent and hypo-autofluorescent spots. Histologic analysis showed progressive loss of photoreceptor nuclei. Immunohistochemistry staining showed Fam161a expression mainly in photoreceptors cilia and the outer plexiform layer (OPL) in WT mice retinas, whereas faint expression was evident mainly in the cilia and OPL of KI mice. Conclusions: The Fam161a - p.Arg512∗ KI mouse model is characterized by widespread retinal degeneration with relatively slow progression. Surprisingly, disease onset is delayed and progression is slower compared with the previously reported knock-out model. The common human null mutation in the KI mouse model is potentially amenable for correction by translational read-through-inducing drugs and by gene augmentation therapy and RNA editing, and can serve to test these treatments as a first step toward possible application in patients. Financial Disclosure(s): The author(s) have no proprietary or commercial interest in any materials discussed in this article.