Human iPSC Modeling Elucidates Mutation-Specific Responses to Gene Therapy in a Genotypically Diverse Dominant Maculopathy

Dominantly inherited disorders are not typically considered therapeutic candidates for gene augmentation. Here we utilized patient iPSC-derived retinal pigment epithelium (iPSC-RPE) to test the potential of gene augmentation versus gene editing to treat Best disease, an autosomal dominant macular dystrophy caused by over 200 missense mutations. Gene augmentation restored calcium-activated chloride channel activity and improved rhodopsin degradation for a subset of dominant mutations depending on the putative role of the affected residue. In comparison, CRISPR-Cas9 editing of the mutant allele resulted in reversal of channel activity deficits for all mutations tested. Importantly, 95% of gene editing events in iPSC-RPE resulted in premature stop codons within the mutant allele, and single cell profiling demonstrated no adverse perturbation of RPE transcriptional programs. These results show that gene augmentation is a viable strategy for a subset of Best disease patients, and that non-responders are candidates for targeted editing of the mutant allele. Similar scenarios likely exist for other genotypically diverse dominant diseases, expanding the therapeutic landscape for patients.