RHO-Associated Retinitis Pigmentosa: Genetics, Phenotype, Natural History, Functional Assays, and Animal Model - In Preparation for Clinical Trials.

Purpose: The purpose of this study was to describe the largest cohort of RHO-associated retinitis pigmentosa (RP) to date, analyzing the spectrum of phenotypes, variants, disease natural history, and genotype-phenotype correlations. Methods: Variants were classified using functional assays, animal models, and published data. Clinical assessments involved visual acuity (LogMAR), dilated fundus examinations, multimodal imaging (spectral-domain optical coherence tomography [SD-OCT] and fundus autofluorescence [FAF]), and international-standard electrophysiology. Cases were described as having generalized RP or sector RP according to fundus examination and imaging data. Longitudinal analysis evaluated progression rates of visual and structural parameters. Results: Two hundred patients (140 families) with likely disease-causing variants in RHO were identified. Positive family history was documented in 78.5% of the cases. Generalized RP was diagnosed in 64%, sector RP in 34.5%, and 1.5% were asymptomatic carriers. Fifty-six variants were identified, 54% were classified as class 2, 14% as class 1, 5% as class 4, and 2% as class 3. Variants in class 1 were associated with earlier symptom onset (mean = 13.5 years), generalized RP, and the worst baseline visual acuity (mean LogMAR = 0.45). Pro347Leu was the most prevalent variant (17%). Longitudinal analysis showed slower progression in sector RP (0.01 LogMAR/year) compared to generalized RP (0.03 LogMAR/year). Imaging revealed distinct phenotypes, including choroideremia-like features in generalized RP and inferior retinal involvement in sector RP that an animal model suggests is light related. Conclusions: RHO-associated RP encompasses a wide phenotypic spectrum with distinct genetic subtypes influencing disease severity and progression. These findings provide critical insights for patient counseling, identifying clinical endpoints, participant stratification, and guiding therapeutic development.