RPE65 variant p.(E519K) causes a novel dominant adult-onset maculopathy in 83 affected individuals.

Recessive RPE65-related retinopathy is an inherited retinal disease (IRD) that is a well-established target for gene therapy. Dominant RPE65-related retinopathy, however, due to Irish founder variant p.(D477G), is extremely rare. Here, we report the discovery, replication and characterization of a novel dominant retinopathy caused by RPE65 variant p.(E519K), identified in 83 individuals of European ancestry across IRD registries (Belgian discovery cohort, n=2,873; replication cohort, n=18,796). Long-read sequencing-based haplotyping revealed a shared region of 464 kb, supporting a founder effect. Genotype-phenotype data support dominant inheritance and phenotypic variability respectively, characterized by late-onset macular dystrophy with two main subtypes, a pathognomonic mottled subtype and a pattern dystrophy subtype. Functional studies showed that the p.(E519K) variant affects RPE65 enzymatic activity, correlating with lower protein expression. Protein modelling and cellular thermal shift assays further supported a destabilizing effect on protein structure. Overall, our work provides strong genetic, clinical, molecular and functional evidence for a novel dominant RPE65 retinopathy in multiple families in Europe and North America due to a Belgian founder variant. This discovery reduces the diagnostic gap in dominant IRD, particularly in individuals of European ancestry. Finally, it lays the foundation for developing therapeutic strategies targeting dominant RPE65 retinopathy.