Divergent Manifestations in Biallelic Versus Monoallelic Variants of RP1-, BEST1-, and PROM1-Associated Retinal...

To compare the clinical characteristics of inherited retinal diseases (IRDs) caused by biallelic versus monoallelic variants in the RP1, BEST1, and PROM1 genes. A total of 52 patients (26 female) with genetically confirmed IRDs were retrospectively selected from the records of the Harkness Eye Institute Clinical Coordinating Center at Columbia University Irving Medical Center. In RP1, 3 individuals with biallelic variants and 22 patients with monoallelic variants classified as pathogenic or likely pathogenic were selected. In BEST1, eight individuals with biallelic variants and nine individuals with monoallelic variants classified as either pathogenic or likely pathogenic were included. In PROM1, four individuals with biallelic variants and six patients with monoallelic variants classified as pathogenic or likely pathogenic were selected. All patients underwent multimodal retinal imaging and, when available, full-field electroretinography (ffERG). In all three genes, individuals with biallelic variants had markedly earlier disease onset and more severe phenotypes. In RP1, on SD-OCT, foveal involvement was observed in all biallelic cases (3/3, 100%) and in 4/22 (18%) monoallelic cases. In BEST1, the average age of onset in the biallelic cohort was 7.12 years, and the average age was 32.7 years in the monoallelic cohort. Four of eight (50%) patients in the biallelic group were additionally found to have widespread serous lesions outside of the central macula. This finding was not observed in the monoallelic group. Three of eight (38%) biallelic BEST1 patients had moderate reductions in their photopic flicker. All monoallelic BEST1 patients had photopic responses within the normal range. PROM1 biallelic cases showed severe functional impairment on ffERG, while most monoallelic cases retained normal responses. In the biallelic cohort, four of four (100%) of patients had severely attenuated or extinguished photopic responses. In the monoallelic PROM1 group, four of five (80%) monoallelic PROM1 patients had normal photopic responses, and P2-2 had mildly attenuated photopic responses. Individuals with biallelic variants exhibited earlier disease onset, more severe retinal degeneration, and significantly reduced retinal function compared with those with monoallelic variants. These observations highlight the role of loss-of-function mechanisms in more aggressive disease courses and underscore the importance of considering zygosity when determining prognosis and planning gene-based therapies.