The mutational landscape of hereditary retinoblastoma and genotype-phenotype associations in Lebanon.

Background: Retinoblastoma is the most common intraocular tumor of childhood. In Lebanon, its incidence is reported at 3.6 per million person-years. This study aimed to characterize the spectrum of RB1 variants in hereditary retinoblastoma and explore genotype-phenotype associations in a Lebanese cohort.

Methods: A retrospective chart review was conducted on retinoblastoma patients enrolled in the Children's Cancer Institute at the American University of Beirut Medical Center from 2012 to 2022. Genetic data (RB1 sequencing and karyotype), clinical characteristics, imaging, treatment, and outcomes were collected and compared between hereditary and sporadic cases, and across different variant types.

Results: A total of 47 patients underwent genetic testing; 63% had hereditary retinoblastoma with 23 patients carrying single nucleotide changes, including four novel mutations, 3 patients with submicroscopic deletions/duplications, and 3 with deletion 13q syndrome. Nonsense mutations were most frequent (52.2%), followed by frameshift and splice-site alterations. Bilaterality was significantly associated with hereditary disease (85.7% vs. 21.1%, p < 0.001), and more common among Syrian patients (p = 0.04). Median age at diagnosis was younger in the hereditary group, although not statistically significant. Enucleation rates (57.1% vs. 78.9%) and vision outcomes were similar across groups (p > 0.05). No significant differences in treatment outcomes were found among different variant types. Among the 3 patients with deletion 13q, two exhibited severe psychomotor and developmental delays.

Conclusion: Hereditary retinoblastoma accounted for 63% of cases, with 23 pathogenic variants including four novel ones. Bilaterality and Syrian nationality were significantly associated with RB1 positivity. This study underscores the importance of comprehensive RB1 genetic testing in improving diagnostic accuracy, guiding treatment decisions, and supporting genetic counselling, particularly in non-Western populations.