As more and more tests for genetic disorders enter medical practice, patients and physicians are increasingly confronted with information that can be extraordinarily difficult to interpret. A report in tomorrow's issue of The New England Journal of Medicine suggests that the medical system may not be adequately prepared for this new era of genetic testing: The study found that a substantial fraction of people who took a test for a rare, inherited form of colon cancer did not receive adequate counseling or even an accurate diagnosis.
A group led by oncologist Francis Giardiello of the Johns Hopkins University School of Medicine in Baltimore analyzed records of 177 patients who were tested in 1995 for familial adenomatous polyposis, a disease that strikes about one in 8000 people and is caused by inherited mutations to the adenomatous polyposis coli gene on chromosome 5. Afflicted teenagers sprout hundreds of benign tumors in the colon and rectum; malignant cancer is detected in most cases by the time a person reaches 50, thus people diagnosed early enough usually have their colon removed.
A genetic test for the disease can confirm a diagnosis or justify use of an invasive colorectal probe. Giardiello's group concluded, however, that the test--which costs between $500 and $750--may not have been warranted for 30 of the patients because they neither came from a family with a history of the disease nor had the hallmark profusion of benign tumors. More disturbing, the researchers found after interviewing clinicians that only 33 patients received counseling before the test, and "the physicians' interpretation of the test results was incorrect" for a whopping 56 patients. That's because the test is tricky. Subjects are free of disease if they test negative for an identified mutation in a diseased family member. But the test misses mutations in about 20% of subjects whose familial mutation is unknown. In these instances, the researchers write, "physicians did not know that a test in which no mutation was detected could represent a false negative result."
These findings are troubling to experts. Says medical ethicist Robert Veatch of Georgetown University, "No doubt the findings suggest a potential problem far beyond this condition."