Résumé
Mutations in USH2A are the most frequent cause of non-syndromic autosomal recessive retinitis pigmentosa (arRP), which is characterized by progressive vision loss due to degeneration of the light-sensing photoreceptor cells. In addition, mutations in USH2A also account for 50% of Usher syndrome type 2 (USH2). Patients with USH2 present with RP associated to ear defects. There are two recurrent USH2A mutations (c.2276G>T and c.2299delG), which account for approximately half the patient cohorts. Interestingly, there exist a clear genotype-phenotype correlation associated to these recurrent (and others) USH2A mutations. Thus, patients presenting with a single copy of a “retina specific allele” (e.g. c.2276G>T) will present with only a retinal phenotype without ear defects. The reason behind this phenomena is currently not understood. We previously reported seamless CRISPR/Cas9-mediated gene correction of these two recurrent mutations in the iPSC of two patients: one presenting with USH2 and the other with arRP. Here, we differentiated the isogenic corrected and non-corrected iPSC lines into retinal organoids to validate our gene-correction strategy and to obtain, for the first time, mature disease models for these two mutations. The characterization of the isogenic corrected and non-corrected retinal organoids show a reversion of the aberrant phenotype in the CRISPR-corrected organoids compared to the USH2A mutant organoids. Moreover, our data shows for the first time that iPSC-derived USH2 and arRP retinal organoids present differential phenotypes. The results presented here validate the CRISPR strategy and provide hope for future therapy. Moreover, insights into the differential pathophysiology of USH2 and arRP will greatly contribute to our understanding on the genotype-phenotype associated to USH2A mutations.