Clinical manifestations of dual‐gene variants in retinitis pigmentosa

PURPOSE: Retinitis pigmentosa (RP) is an inherited retinal disease (IRD), whereby each affected individual typically harbours pathogenic variants in a single causative gene, yet the disorder exhibits marked genetic heterogeneity, with more than 100 genes reported to underlie RP. Dual-gene defect constellations are rare but may modify disease presentation, complicating diagnosis, prognosis and therapeutic decision-making. This study aimed to characterize the clinical and genetic effects of dual-gene variants in patients with RP as the lead diagnosis. METHODS: We retrospectively analysed 10 affected individuals and their parents from eight families with confirmed dual-genotype constellations in RP-associated genes. Ophthalmic evaluation included best-corrected visual acuity (BCVA), visual fields, multimodal imaging, electroretinography (ERG) and full-field stimulus threshold testing (FST). Genetic analyses comprised whole genome sequencing and targeted segregation studies; for the latter, long-read sequencing was used to clarify cis/trans variant configuration. RESULTS: Genes involved were CEP290, RCBTB1, ABCA4, PDE6A, CRB1, EYS, PRPH2, MYO7A, RS1, USH2A, MT-TL1, RHO and BEST1, in various genotype constellations. Phenotypes ranged from early-onset severe rod-cone dystrophy to late-onset mild RP, largely reflecting gene-specific effects (e.g. EYS > CRB1 > PRPH2) and their interactions. Long-read sequencing revealed ABCA4 variants in cis, explaining asymptomatic carriers and informing gene therapy eligibility. Functional retinal testing highlighted gene-specific patterns, including macular preservation in EYS-driven RP and Best disease-associated macular changes. CONCLUSION: Dual-gene variant constellations contribute to heterogeneous RP phenotypes. Integrating comprehensive genetic analysis with detailed clinical assessment is critical to define gene-specific contributions, inform prognosis, guide clinical management and determine eligibility for emerging gene-based therapies.