Paper II — 2022 July (Supplementary) (2019 Scheme) — Q17
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Paper II
2022 July (Supplementary) (2019 Scheme) · 100 marks · 180 min
Question
What is the genetic basis of Retinoblastoma
Q171 marks
Answer
Retinoblastoma follows Knudson’s “two-hit” hypothesis, requiring inactivation of both alleles of the RB1 tumour suppressor gene (chromosome 13q14). In the hereditary form, the first mutation is inherited in the germline (present in all cells), requiring only a single somatic “second hit” in a retinal cell to cause tumour formation — leading to earlier onset, bilateral/multifocal tumours, and increased risk of secondary malignancies. In the sporadic form, both hits occur somatically in the same retinal cell, resulting in unilateral, later-onset disease.
