Truth and confidentiality without harm

Case vignette: sharing unanticipated genetic information. The Questor family has experienced an unusual number of malignancies in the past two generations and has been advised by an oncologist that the p53 oncogene known as Li-Fraumeni Syndrome may be present in the family genome. The option of predictive genetic testing has been raised and several branches of the family have chosen to undergo screening to determine whether they are at risk for cancer because of the gene. Roger and Liz Questor have arranged for screening of themselves and their three children, ages 12, 10, and 7. The couple has, by all appearances, been happily married for 14 years. None of the family members are found to carry the oncogene; however, the geneticist conducting the analyses has made an interesting incidental discovery. The 10-year-old child is not the biological progeny of Roger Questor. Although the 12- and 7-year-olds are clearly the biological children of the couple, it is evident that the 10-year-old born to Liz Questor was fathered by a person other than Roger. What are the ethical obligations of the geneticist with respect to any sharing or disclosure of the information that has been discovered incidentally? What course of action, if any, do you recommend?