Genomic Landscape of Sporadic Retinitis Pigmentosa: Findings from 877 Spanish Cases.

Purpose: We aimed to unravel the molecular basis of sporadic retinitis pigmentosa (sRP) in the largest cohort reported to date.

Design: Case series.

Participants: A cohort of 877 unrelated Spanish sporadic cases with a clinical diagnosis of retinitis pigmentosa (RP) and negative family history.

Methods: The cohort was studied by classic genotyping or targeted next-generation sequencing (NGS). Multiplex ligation-dependent probe amplification (MLPA) and array-based comparative genomic hybridization were performed to confirm copy number variations detected by NGS. Quantitative fluorescent polymerase chain reaction was assessed in sRP cases carrying de novo variants to confirm paternity.

Main Outcome Measures: The study of the sRP cohort showed a high proportion of causal autosomal dominant (AD) and X-linked (XL) variants, most of them being de novo.

Results: Causative variants were identified in 38% of the patients studied, segregating recessively in 84.5% of the solved cases. Biallelic variants detected in only 6 different autosomal recessive genes explained 50% of the cases characterized. Causal AD and XL variants were found in 7.6% and 7.9% of cases, respectively. Remarkably, 20 de novo variants were confirmed after trio analysis, explaining 6% of the cases. In addition, 17% of the solved sRP cases were reclassified to a different retinopathy phenotype.

Conclusions: This study highlights the clinical utility of NGS testing for sRP cases, expands the mutational spectrum, and provides accurate prevalence of mutated genes. Our findings evidence the underestimated role of de novo variants in the etiology of RP, emphasizing the importance of segregation analysis as well as comprehensive screening of genes carrying XL and AD variants in sporadic cases. Such in-depth study is essential for accurate family counseling and future enrollment in gene therapy-based treatments.