For the benefit of all.

Margaret W, now forty-one, has had regular mammograms since she was in her mid-thirties, when she discovered a small lump in her left breast. Although the lump proved to be a benign cyst, on the basis of her family history her physician had strongly recommended that she continue routine annual mammograms. Two of her mother's three sisters had been treated for breast cancer (one at age 45, the other at 48) and her maternal grandmother was diagnosed with breast cancer at age sixty-seven. The grandmother's sister had died of ovarian cancer at fifty-three. Cancer has now appeared in Margaret's own generation: not long ago her thirty-seven-year-old cousin Emily underwent a bilateral total mastectomy for infiltrating adenocarcinoma. Emily's oncologist, aware of the family's history would like to refer her - and her relatives - to a geneticist colleague studying inherited susceptibility to breast and ovarian cancer. There is evidence, the oncologist told Emily, that about one in 200 women have inherited such susceptibility. The colleague he would like her to see is studying BRCA1, a newly identified gene associated with both breast and ovarian cancer. While researchers haven't yet isolated the precise sequence of BRCA1 (and so can't screen for it directly), he noted, linkage analysis in extended families with unusual cancer histories can reveal familial markers associated with, the gene. Since Dr. Ayers, the geneticist, is willing to provide families with information about any markers such analysis uncovers, in participating in die research Emily, Margaret, and their relatives could not only provide data that might someday help other women avoid breast cancer, but could benefit directly themselves in being able to plan their care more thoughtfully with their physicians. Her cousin came to Margaret to talk over the idea of participating in linkage studies. It would involve all members of their extended family in one way or another, and Margaret isn't sure they would want to or should take part. On die other hand, joining the research and being counseled about their individual risks might mean better health for each of them - Margaret is especially concerned about what the family history suggests for her two daughters, aged twenty and seventeen. In talking together Margaret and Emily realize they don't know all the questions they should ask to make a wise decision. What does being "genetically susceptible" to breast cancer really mean? What other implications might taking part in this research hold for them and their families? Who will give them the best counsel in making a decision? This case foretells an imminent shift of emphasis in medical genetics. In marked contrast to the traditional focus of genetic counseling n providing diagnosis and reproductive risks for rare genetic conditions, the identification of genes associated with susceptibility to common disorders, such as breast cancer, will propel this specialty into the area of preventive health care. But due to the significance of factors other than genetics in disease etiology, genetic susceptibility information - in the form of genes or DNA sequences associated with common diseases - will be inherently limited in predictive value. Individuals who are carriers of a genetic susceptibility trait might never experience the condition with which the trait has been associated. While there may seem to be little appreciable difference, testing for genetic susceptibility is unlike testing for other types of susceptibility. An important difference is that instead of measuring the end result of combined environmental and/or genetic factors at a particular moment in time, such as with cholesterol testing, only genetic material, immutable and unchangeable over time, is assessed. Unlike cholesterol tests, which generate a course of action (such as diet and exercise recommendations or drug therapies), genetic information itself is resistant to human intervention. …