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

Abstract

Dominantly inherited disorders are not typically considered therapeutic candidates for gene augmentation (GA). We tested whether GA or genome editing (GE) could serve as a solo therapy for autosomal dominant Best disease (adBD), a macular dystrophy linked to over 100 mutations in the BEST1 gene, which encodes a homo-pentameric calcium-activated chloride channel (CaCC) in the retinal pigment epithelium (RPE). Since no suitable animal models of adBD exist, we generated RPE from patient-derived induced pluripotent stem cells (iPSC-RPE) and found that GA restored CaCC activity and improved rhodopsin degradation in a subset of adBD lines. iPSC-RPE harboring adBD mutations in calcium clasp or chloride binding domains of the channel, but not in a putative structural region, were responsive to GA. However, reversal of the iPSC-RPE CaCC deficit was demonstrated in every adBD line following targeted CRISPR-Cas9 GE of the mutant allele. Importantly, 95% of GE events resulted in premature stop codons within the mutant allele, and single cell profiling demonstrated no adverse perturbation of RPE transcriptional programs post-editing. These results show that GA is a viable approach for a subset of adBD patients depending on the functional role of the mutated residue. Further, GA non-responders are candidates for targeted GE of the mutant allele. Similar scenarios likely exist for other genotypically diverse dominant diseases, expanding the therapeutic landscape for affected patients.