Genetics of retinoblastoma.

Retinoblastoma may be due to (1) a somatic mutation, which is not hereditary, (2) a germinal mutation, which is dominantly inherited, and (3) a deletion of the long arm of chromosome 13. In unilateral cases of retinoblastoma, the risk for the offspring is 5-6%, as 10-15% of these cases are due to a germinal mutation. In all the bilateral cases and in the unilateral hereditary cases, the risk for the offspring or the sibs is 40-50% depending on the penetrance of the gene.