Sarah, a 40-year-old mother of three, has found out from various tests that she has an elevated risk of Alzheimer’s disease, as well as of breast cancer. Does she have a legal or moral obligation to tell her children or close relatives that they, too, might be at high risk of getting these illnesses in the future?

The legal issue is straightforward: no court has held an individual liable for failing to warn a relative about genetic test results. The moral issue depends on many factors, including the severity of a genetic condition, the number of years before it is likely to produce symptoms, and whether the condition is treatable. The nature of relationships (parent and child) and their emotional closeness matter, too, as do relatives’ ages, their interest in knowing about the chance of future ills, and the individual’s own concern about not divulging his or her personal problems.

The nature of the danger often plays a strong role. In rare cases, genetic conditions can be lethal if combined with environmental stressors. For example, individuals with the genetic mutation for malignant hyperthermia can die during surgery if certain anesthesia is used. People with hypertrophic cardiomyopathy can suffer sudden death from strenuous exercise. The potential for these types of harm warrant notifying at-risk relatives.

Yet sharing one’s genetic information with family members can be perilous. Testing may reveal, for instance, that the man everyone thought was a child’s father actually is not, sending a family into turmoil. Genetic counselors can help people decide whether to undergo genetic testing and how to respond to possible results, but currently only 2,500 counselors practice in the U.S. The most common mistake is getting tested and waiting for results before considering what to do. Anyone contemplating testing should determine in advance whether to share the results with close relatives. There is no simple answer. The best advice is to consult with professionals and think ahead about the possible consequences.