Genome Editing Therapy for Usher Syndrome

Usher Syndrome (USH) is a genetic disorder characterized by progressive hearing and vision loss, with an estimated prevalence of approximately 1 in 20,000 individuals. The most common subtype, Usher syndrome type II (USH2), is primarily associated with
mutations in the USH2A gene, which cause Usher syndrome type IIA (USH2A). USH2A mutations account for over half of all USH2 cases and are strongly linked to retinitis pigmentosa. Efforts to develop treatments for USH2A-related disease face significant challenges due to the gene’s large size, extensive mutational spectrum, and limited understanding of its pathogenic mechanisms. Currently, no approved treatments exist to alleviate the retinal symptoms associated with USH2A mutations.

One major challenge is the large size of the USH2A gene (over 15.6kb), which exceeds the carrying capacity of traditional adeno-associated viral (AAV) vectors. CRISPR genome editing opens a new avenue to therapeutic development. USH2A exon 13 is a hotspot region for pathogenic mutations accounting for 25-50% of the total mutations, making it a key target for therapeutic intervention. Here, we propose to evaluate the efficacy of various genome-editing strategies to correct mutations in USH2A exon 13 with the goal of developing a therapeutic approach to mitigate or slow the progression of retinal degeneration. We aim to achieve clinically relevant mutation correction by systematically testing multiple genome-editing techniques, including CRISPR-mediated non-homologous end joining (NHEJ), base editing (BE), and prime editing, to restore normal USH2A protein expression. BE will be employed to introduce precise modifications at splicing sites, thereby facilitating exon 13 skipping as a therapeutic strategy. In parallel, PE will be utilized to achieve precise correction of the pathogenic 2299delG mutation within exon 13.

Another challenge is the significant genomic differences between mice and humans, which complicates preclinical evaluation. To address this, we have established patient-derived retinal organoids and developed a humanized mouse model carrying USH2A exon 13 mutations, which exhibits congenital hearing loss and subtle photoreceptor abnormalities. These models are invaluable tools for effectively evaluating and advancing these gene therapies toward clinical translation.

Our innovative approach integrates diverse gene-editing strategies to address USH2A- related vision loss, with the overarching goal of reducing the burden of blindness, improving patient quality of life, and advancing precision medicine for inherited retinal diseases.