Alterations in the RB1 gene in Pakistani patients with retinoblastoma using direct sequencing analysis

PURPOSE: Retinoblastoma (RB) is a rare intraocular malignant tumor of the developing retina with an estimated incidence of 1:20,000 live births in children under the age of 5 years. In addition to the abnormal whitish appearance of the pupil or leukocoria, strabismus has also been reported as a clinical symptom of the disease. RB1 is the first cloned tumor suppressor gene, and mutational inactivation of this gene is responsible for the development of RB during early childhood. The purpose of this study was to identify mutational alterations in the RB1 gene in Pakistani patients with RB. METHODS: During this study, 70 clinically evaluated patients with RB were recruited from different regions of Pakistan. The cases included 23 sporadic bilateral (32.9%), 34 sporadic unilateral (48.6%), nine familial bilateral (12.8%), and four familial unilateral (5.7%) cases. Constitutional causative mutations in the RB1 gene were screened via direct sequencing of all RB1 exons and their flanking regions. RESULTS: In this report, genetic testing resulted in the identification of 18 mutations in 25 patients with RB including six novel RB1 mutations. Of the total mutations identified, 13 (72.22%) were found to be null mutations caused by nine nonsense, three deletions, and one insertion. Two (11.11%) missense, two (11.11%) splice site mutations, and one (5.55%) base substitution in the promoter region were also found. Moreover, ten intronic variants were identified, one of which is novel. CONCLUSIONS: Molecular screening and identification of these mutations in Pakistani patients with RB provide the mutational variants of the RB1 gene in the Pakistani population. The detection of oncogenic mutations in patients with RB and genetically predisposed individuals is a major step in clinical management, prognosis, follow-up care, accurate genetic counseling, and presymptomatic diagnosis of RB.