Mapping RB1 gene mutations in retinoblastoma: a study of 200 cases from North India.

Retinoblastoma is a pediatric ocular malignancy caused by biallelic inactivation of the RB1 gene, with genetic testing crucial for determining heritability. This retrospective observational study analyzed the genotypic and phenotypic profiles of 200 RB patients from North India who underwent genetic testing at a tertiary eye hospital between January 2022 and April 2024. Targeted RB1 gene analysis was performed using next-generation sequencing on blood samples, with methylation specific-multiplex ligation-dependent probe amplification detecting large deletions or duplications. Phenotypic features, including age of onset, laterality, disease severity, metastasis, and recurrence, were assessed. Among 200 patients, 113 had unilateral RB, 85 bilateral, and two trilateral, with mean onset ages of 33 months for unilateral and 14 months for bilateral cases. Intraocular tumors were present in 84%, extraocular extension in 16%, and metastasis in 16% of cases. Pathogenic RB1 variations were identified in 48% of patients, predominantly in bilateral cases (77.08%). A trend toward mutation clustering in exons 14-21 was observed in 57% of patients. While bilateral disease showed a statistically significant correlation with genotype for non-sense variations (p = 0.05); no other clinical features were linked to specific mutations. This study highlights unique regional genotypic patterns and emphasizes the potential for cost-effective testing strategies in resource-limited settings.