RPE65 Variant p.(E519K) Causes a Novel Dominant Adult-Onset Maculopathy in 83 Affected Individuals

PURPOSE. Recessive RPE65-associated retinopathy is a well-known target for gene therapy, whereas dominant RPE65-associated retinopathy, due to the Irish founder variant p.(D477G), has been reported only once until now and is very rare. Here, we present the discovery of a novel, second dominant RPE65-associated retinopathy caused by variant c.1555G>A, p.(E519K). METHODS. Genomic data was investigated in a Belgian discovery cohort (n = 2873) and an international replication cohort (n = 18,796) with inherited retinal disease (IRD). Heterozygous p.(E519K) individuals underwent extensive phenotyping. Haplotype phasing was based on long-read sequencing and microsatellite analysis. Variant p.(E519K) was assessed in vitro using an enzymatic assay, Western blotting, co-immunoprecipitation, cellular thermal shift assay (CETSA), minigene assays, and in silico using protein modeling (AlphaFold). RESULTS. The monoallelic p.(E519K) variant was found in 83 affected individuals from Belgium, the Netherlands, France, and Canada, all of European ancestry. A shared region of 464 kilobases (kb) confirmed a founder effect. Variant p.(E519K) lowers RPE65 protein expression and enzymatic activity, with altered protein stability predicted and experimentally confirmed. Genotype-phenotype data support dominant inheritance and phenotypic variability, respectively, characterized by late-onset macular dystrophy with two main subtypes. CONCLUSIONS. The discovery of a dominant RPE65-IRD due to founder variant p.(E519K) reduces the diagnostic gap in dominant IRD and highlights a novel target for therapy.