In families with genetic disorders due to a known genetic mutation, presymptomatic genetic testing can lead to early detection and treatment of inherited disorders that may manifest later in life. The health benefits for family members at increased risk, however, is limited by the predictive value of the genetic test, the availability of effective treatments, and individuals' and families' willingness to undergo genetic testing in the first place. This Issue Brief describes the case of a genetic condition for which genetic screening of family members is clearly useful, and just as clearly underused. It explores the barriers to the use of genetic screening and has implications for the future as genetic technologies become more complex and produce more uncertainty.