Usher syndrome is the most common form of hereditary deaf-blindness. The three subtypes are caused by pathogenic variants in various genes, one of the most frequently affected being USH2A (Usherin). In addition, biallelic variants in USH2A are also the most common cause of non-syndromic retinitis pigmentosa. In up to 4% of Usher patients but also RP patients, a deep intronic variant (USH2A c.7595-2144A>G) is the underlying genetic cause.

This variant causes an mRNA splicing defect resulting in aberrant or truncated Usherin protein. Our therapeutic strategy to eliminate this mutation and correct mRNA maturation is based on the CRISPR technology, utilizing novel enhanced-deletion synthetic RNA-guided nucleases (short EDsRGNs). These bioengineered gene scissors induce enhanced deletions and offer better safety features compared to alternative CRISPR-Cas methods. Moreover, they can be packaged into adeno-associated viruses (AAVs) for in vivo delivery.

The most common inherited retinal disease (IRD) and the major cause for blindness in humans is retinitis pigmentosa (RP). Approximately 25% of the reported cases of autosomal dominant RP are caused by pathogenic variants in rhodopsin (RHO), which typically act as gain-of-function or dominant-negative alleles. Since one wildtype allele would supply for sufficient protein function, a selective inhibition of pathogenic allele expression is desirable. To enable an application of this strategy to a large subcohort of RHO-adRP cases, which exhibits >200 different disease-causing variants, we focus on a mutation-independent antisense oligonucleotide (AON) approach. Identifying both potent and specific AONs will enable us to specifically suppress the translation of mutant rhodopsin protein, potentially alleviating symptoms for numerous RP patients.