Genome Editing in Patient iPSCs Corrects the Most Prevalent Mutations and Reveals Intriguing Mutant mRNA Expression Profiles.

Inherited retinal dystrophies (IRDs) are characterized by progressive photoreceptor degeneration and vision loss. Usher syndrome (USH) is a syndromic IRD characterized by retinitis pigmentosa (RP) and hearing loss. USH is clinically and genetically heterogeneous, and the most prevalent causative gene is . mutations also account for a large number of isolated autosomal recessive RP (arRP) cases. This high prevalence is due to two recurrent mutations, c.2276G>T and c.2299delG. Due to the large size of the cDNA, gene augmentation therapy is inaccessible. However, CRISPR/Cas9-mediated genome editing is a viable alternative. We used enhanced specificity Cas9 of (eSpCas9) to successfully achieve seamless correction of the two most prevalent mutations in induced pluripotent stem cells (iPSCs) of patients with USH or arRP. Our results highlight features that promote high target efficacy and specificity of eSpCas9. Consistently, we did not identify any off-target mutagenesis in the corrected iPSCs, which also retained pluripotency and genetic stability. Furthermore, analysis of expression unexpectedly identified aberrant mRNA levels associated with the c.2276G>T and c.2299delG mutations that were reverted following correction. Taken together, our efficient CRISPR/Cas9-mediated strategy for mutation correction brings hope for a potential treatment for USH and arRP patients.