A study on genetic variants associated with retinoblastoma in a cohort of Sri Lankan patients

Introduction: Retinoblastoma is the most common intraocular malignancy of infancy and childhood (<5yrs) with 8000-9000 cases detected every year. The mean age of diagnosis is 18 months. Symptoms of retinoblastoma range from Leukocoria, red eye, poor vision and squint to glaucoma and proptosis in advanced cases. Different genes such as KIF14, E2F3, DEK, MYCN and CDH11 have been found to be related to this cancer, but the RB1 gene shows the most significant association throughout the world. The RB1 gene which was the 1st tumor suppressor gene to be ever recognized is located at chromosome 13q 14.2 locus and consists of 27 exons and 27 introns. When a single RB1 allele is having a variant, the individual will be exposed to Retinoblastoma and when the balanced normal allele is lost as well for a cancer predisposing variant, the Retinoblastoma will develop. Retinoblastoma cases are reported throughout the entire region across Asia with the highest incidence in India. But still the Asian region is having limited information and poor Retinoblastoma recognition leading to increased mortality rates in the developing countries. This study aims to figure out genetic variants associated with Retinoblastoma in Sri Lankan population in order to support the screening/ testing and early recognition by molecular genetic testing/ screening which will help to reduce the mortality rate and save the vision of Sri Lankan Retinoblastoma patients.Materials and methods: The genetic variants associated with Retinoblastoma were identified through a comprehensive literature review and they were filtered for Asia/ South Asia. Most significant 02 variants were selected out of them (rs121913300 and rs1131690863) and their allele frequencies were manually computed based on the genotyping results reported in RB1 studies across Asia/South Asia. In line with literature review, the availability of resources and the meeting of research criteria, Tetra-primer amplification refractory mutation system PCR (T-ARMSPCR) was determined as the most effective genetic assay for this study. Primers were designed accordingly for the selected 02 variants. After optimizing the PCR protocol, 59 anonymous retinoblastoma patient-blood samples obtained from the Human Genetics Unit, Faculty of Medicine, University of Colombo, Sri Lanka were genotyped and a descriptive study was carried out. The genotyping results were further validated by Sanger Sequencing.Results: All the Retinoblastoma patients were homozygous for the ancestral allele in terms of both the variants rs121913300 and rs1131690863. The manually computed minor allele frequencies determined that both the variants were rare in the Sri Lankan community. Their genotype distributions were in Hardy-Weinberg Equilibrium; hence will continue the same across generations.Discussion and conclusion: The study found that rs121913300 and rs1131690863 were rare among the Sri Lankan patients and therefore these 02 variants would be less important in developing screening tests for the Sri Lankan community.