Questions Asked by Retinoblastoma Families

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Retinoblastoma and the RB1 Gene
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Testing Unilaterally Affected Individuals when there is no Tumor DNA
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Questions Asked by Retinoblastoma Families

  1. My six-year-old child had unilateral retinoblastoma. We didn't have genetic testing at the time her eye was enucleated, so there is no tumor tissue available. Now we would like to know if she carries a germline mutation. Our only other child is 4 years old and shows no sign of retinoblastoma. Is it better to wait to test until our daughter is closer to child-bearing age, in case advances in the field make testing more conclusive?

    A: It is better to test your daughter sooner rather than later.

    While it is certainly true that genetic testing is always improving, our lab banks DNA for every person whose mutation cannot be identified. As each new method is developed and implemented, we apply it to such DNA samples at no extra charge and report any new findings right away.

    Testing sooner rather than later also improves the care for your four-year-old son. If he carries the same mutation as his sister, he is very likely to have tumors. If he does not carry the same mutation as his sister, he is only at population risk (1 in 15,000) to have retinoblastoma, so under current clinical standards, he does not need EUA's.

    Last, it is also important for your daughter's care to know whether she carries a germline mutation. This knowledge is important to the ophthalmologist's treatment plan, and if she has a germline mutation, your daughter is at higher risk of secondary tumors should she be exposed to radiation.



  2. What is the probability that your lab will find a mutation for a child diagnosed with unilateral, unifocal retinoblastoma if you are sent blood alone and not a sample of tumor tissue?

    A: It is important to preserve retinoblastoma tumor tissue whenever possible by flash freezing, and not by formalin fixation and paraffin embedding. Access to tumor DNA allows much more powerful analysis, and we seem to learn something new about retinoblastoma from almost every tumor studied.

    If no tumor is available, then there are three outcomes possible when we study DNA from blood alone for a unilaterally affected individual with no family history of retinoblastoma:

    • (14% chance) we identify a germline mutation in DNA extracted from the person's blood.


    • (85% chance) we find no mutation because there is no germline mutation in the person's DNA. His or her retinoblastoma is somatic.


    • (1% chance) our methods cannot detect the germline mutation that leads to the person's retinoblastoma.


    Even though this analysis is not as powerful as it would be with access to tumor tissue, it will either identify a mutation or reduce the risk of a germline mutation from 15% to 1%.

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