Retinoblastoma in twins: Risk assessment of genotypic variants

• Main Authors: Vishal Raval, Meghan DeBenedictis, Randy Bowen, Hansell Soto, Jacquelyn Davanzo, Arun Singh
• Format: Article
• Language: English
• Published: Wolters Kluwer Medknow Publications 2021-01-01
• Series: Indian Journal of Ophthalmology
• Subjects: genetic testing; germline; mosaic; retinoblastoma; twins
• Online Access: http://www.ijo.in/article.asp?issn=0301-4738;year=2021;volume=69;issue=5;spage=1230;epage=1233;aulast=Raval

Purpose: To describe methods of risk assessment in twins with retinoblastoma (RB). Methods: A case series of four RB probands with a twin sibling. Family status, clinical presentation, and RB1 germline status-based risk assessment were analyzed. Results: Two pairs had a positive family history (unilateral and bilateral RB in one of the parents (#1 and #2, respectively) and two pairs (#3 and #4) were sporadic. One of the familial twins (#1) had a high risk (90%) of manifesting RB in the twin. The other case (#2) with an absent RB1 germline mutation in the twin had a 0% risk of developing RB. Among sporadic cases of twins (#3), genetic testing did not identify a germline mutation (tumor sample unavailable) in the proband which downgraded the risk of germline mutation from 15% to <1%. The twin never developed RB (5 years of age at last follow-up). Pathogenic mosaicism for germline RB1 mutation (c.1723C>T) could be identified (tumor tissue available) in the proband (# 4). Identical germline mutation (and RB tumor) was also noted in the twin. In each case, there was concordance between the assessed risk and manifestation of RB. Conclusion: Assessment of risk of RB in a twin presents with a unique challenge. Depending upon the genotype variant, the risk of developing RB can vary from 0% to 90%. In addition to family history, clinical manifestation in the proband, zygosity status, and RB1 germline status are critical in formulating risk-appropriate surveillance guidelines.