Layperson abstract

Inherited retinal dystrophies (IRD) are a heterogeneous group of genetic disorders with an estimated prevalence of 1 in 3,000-4,000 individuals. Retinitis pigmentosa (RP) is the most common subform of IRD and characterized by nightblindness and progressive degeneration of rod photoreceptors which leads to loss of peripheral vision (tunnel vision), and eventually blindness in advanced stages. Overall, dominant inherited RP (adRP) accounts for 11.5% of all IRDs and RHO is the most commonly mutated gene in adRP. To date, more than 240 likely disease-causing RHO variants have been characterized, highlighting the considerable genetic heterogeneity of the mutational spectrum typical of RHO. This heterogeneity has hindered the development of therapeutic approaches applicable to a larger fraction of patients with RHO mutations. By applying a novel genome editing approach which targets frequent DNA polymorphisms in the RHO gene, we aim to selectively disrupt the disease-causing copy of the RHO gene, thereby establishing a therapeutic concept that is independent from individual mutations. On the whole, such an approach would enable to address more than 40% of RHO-adRP cases, giving hope to a large number of patients.

Scientific abstract

Inherited retinal dystrophies (IRD) are a heterogeneous group of genetic disorders with an estimated prevalence of 1 in 3,000-4,000 individuals. Retinitis pigmentosa (RP) is the most common subform of IRD and characterized by night blindness and progressive degeneration of rod photoreceptors which leads to loss of peripheral vision, and eventually blindness in advanced stages. In our large local cohort, dominant inherited RP (adRP) accounts for 11.5% of all IRDs. Mutations in RHO encoding the apo-protein of the rod photoreceptor visual pigment is the most common cause of adRP. The Human Genome Mutation Database lists 247 likely disease-causing RHO variants, the vast majority (>200) being missense variants associated with adRP. Since dominant RHO mutations typically act as gain-of-function or dominant-negative mutations, we propose to apply a novel bioengineered CRISPR/Cas genome editing variant to selectively disrupt RHO mutant alleles while preserving the integrity of wild-type allele. Specifically, different frequent heterozygous SNPs in cis with the specific mutations are targeted to disrupt the activity of mutant RHO. On the whole, the cumulative frequency of the selected SNPs is estimated to be present in >40% of the patient population, enabling to address a large sub cohort of RHO-adRP cases. Considering future in vivo application and clinical translation potential of this approach, we will employ novel bioengineered CRISPR/Cas variants that are amenable for delivery via recombinant AAV vectors. Patient-derived cellular models will be implemented for the assessment and validation of the proposed mutation-independent genome editing approach.