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Retinoblastoma Gene

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Amit Maity, MD
Last Modified: November 1, 2001

Dear OncoLink "Ask the Experts,"
I had bilateral retinoblastoma as a child. Would I, as a woman, be any more likely than a man to pass retinoblastoma on to my child if I were to conceive, or are the odds the same, regardless of which parent has the gene?

Amit Maity, MD, Assistant Professor of Radiation Oncology at the Hospital of the University of Pennsylvania, responds:

The odds are the same regardless of the sex of the parent. Retinoblastoma is not a sex-linked disease. In other words, the gene that is mutated in this disease, Rb gene, does not reside on either the X or the Y chromosome. In fact, the Rb gene resides on chromosome 13, and there are normally two copies of the Rb gene in somatic cells (cells other than sperm or eggs) in the body (one inherited from the mother and the other from the father).

In a person with bilateral retinoblastoma, the assumption is that one of the two Rb genes in the somatic cells throughout their body are mutated. When sperm or egg cells are made; only one copy of the Rb gene is passed on through the process of meiosis. Therefore, there is a 50% chance that any given sperm or egg from the affected parent carries the defective Rb gene. Hence, the child has a 50% chance of inheriting the defective Rb gene (assuming that the other parent has two normal Rb genes). Unfortunately, almost all children who inherit a single defective Rb gene will go on to develop retinoblastoma.