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There is an emblematic clinical and genetic heterogeneity associated with inherited retinal diseases (IRDs). The most common form is retinitis pigmentosa (RP), a rod-cone dystrophy caused by pathogenic variants in over 80 different genes. Further complexifying diagnosis, different variants in individual RP genes can also alter the clinical phenotype. USH2A is the most prevalent gene for autosomal-recessive RP and one of the most challenging because of its large size and, hence, large number of variants. Moreover, USH2A variants give rise to non-syndromic and syndromic RP, known as Usher syndrome (USH) type 2, which is associated with vision and hearing loss. The lack of a clear genotype-phenotype correlation or prognostic models renders diagnosis highly challenging. We report here a long-awaited differential non-syndromic RP and USH phenotype in three human disease-specific models: fibroblasts, induced pluripotent stem cells (iPSCs), and mature iPSC-derived retinal organoids. Moreover, we identified distinct retinal phenotypes in organoids from multiple RP and USH individuals, which were validated by isogenic-corrected controls. Non-syndromic RP organoids showed compromised photoreceptor differentiation, whereas USH organoids showed a striking and unexpected cone phenotype. Furthermore, complementary clinical investigations identified macular atrophy in a high proportion of USH compared with RP individuals, further validating our observations that USH2A variants differentially affect cones. Overall, identification of distinct non-syndromic RP and USH phenotypes in multiple models provides valuable and robust readouts for testing the pathogenicity of USH2A variants as well as the efficacy of therapeutic approaches in complementary cell types., Competing Interests: C.S.-S. and V.K. are the inventors of a published patent on genome editing for USH2A (WO/2020/221832)., (© 2023 The Authors.)

We report here the generation of the human iPSC line INMi005-A from a patient with non-syndromic autosomal recessive retinitis pigmentosa caused by compound heterozygous mutations in the USH2A gene. The reprogramming of primary human dermal fibroblasts was performed using the non-integrative Sendai virus method and the OSKM transcription factor cocktail. The generated INMi005-A iPSC line is pluripotent and genetically stable, and will represent a valuable tool for understanding the pathophysiology associated with USH2A mutations., (Copyright © 2022. Published by Elsevier B.V.)

Retinitis pigmentosa (RP) is an inherited retinal dystrophy that causes progressive vision loss. The G56R mutation in NR2E3 is the second most common mutation causing autosomal dominant (ad) RP, a transcription factor that is essential for photoreceptor development and maintenance. The G56R variant is exclusively responsible for all cases of NR2E3 -associated adRP. Currently, there is no treatment for NR2E3 -related or, other, adRP, but genome editing holds promise. A pertinent approach would be to specifically knockout the dominant mutant allele, so that the wild type allele can perform unhindered. In this study, we developed a CRISPR/Cas strategy to specifically knockout the mutant G56R allele of NR2E3 and performed a proof-of-concept study in induced pluripotent stem cells (iPSCs) of an adRP patient. We demonstrate allele-specific knockout of the mutant G56R allele in the absence of off-target events. Furthermore, we validated this knockout strategy in an exogenous overexpression system. Accordingly, the mutant G56R-CRISPR protein was truncated and mis-localized to the cytosol in contrast to the (peri)nuclear localizations of wild type or G56R NR2E3 proteins. Finally, we show, for the first time, that G56R iPSCs, as well as G56R-CRISPR iPSCs, can differentiate into NR2E3-expressing retinal organoids. Overall, we demonstrate that G56R allele-specific knockout by CRISPR/Cas could be a clinically relevant approach to treat NR2E3 -associated adRP.

We generated an induced pluripotent stem cell (iPSC) line from a patient with non-syndromic retinitis pigmentosa who is a compound heterozygote for the two most frequent USH2A variants, c.2276G > T and c.2299delG localized in exon 13. Patient fibroblasts were reprogrammed using the non-integrative Sendai virus reprogramming method and the human OSKM transcription factor cocktail. The generated cells were pluripotent and genetically stable. This iPSC line will be an important tool for studying the pathogenesis of these USH2A mutations and for developing treatments that, due their high prevalence, will target a large patient population., (Copyright © 2018 The Authors. Published by Elsevier B.V. All rights reserved.)